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Tetrahedron
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  • Graphical abstract TOC
    • Abstract: Publication date: 8 March 2019Source: Tetrahedron, Volume 75, Issue 10Author(s):
       
  • Graphical abstract TOC
    • Abstract: Publication date: 8 March 2019Source: Tetrahedron, Volume 75, Issue 10Author(s):
       
  • Graphical abstract TOC cont'd
    • Abstract: Publication date: 8 March 2019Source: Tetrahedron, Volume 75, Issue 10Author(s):
       
  • Hyperconjugation effect on diene reactivity in
           1-methyltetrazolo[5,1-a]isoindole-derived amides and thioamides
    • Abstract: Publication date: Available online 15 February 2019Source: TetrahedronAuthor(s): Tatyana V. Yegorova, Svitlana V. Shishkina, Roman I. Zubatyuk, Magdalina D. Tsapko, Oleg V. Shishkin, Zoia V. Voitenko Optimized synthesis of 1-methyltetrazolo[5,1-a]isoindole-derived amides and thioamides was elaborated. Based on 13C NMR spectroscopy and X-Ray diffraction studies data, it was proposed that zwitterionic resonance structures contributed significantly to the structure of these compounds. Geometry optimization was performed in vacuo using m06-2x/cc-pvtz method taking into account polarizing effect of environment (PCM model) and specific intermolecular interactions. Electronic density distribution in these molecules was analyzed using NBO method. Using Δ(HOMOdiene–LUMOdienophile) for amides and thioamides in vacuo and in a protic solvent, possibility of Diels–Alder reaction was evaluated. Energies of π-π conjugation and n→σ* hyperconjugation for the amide derivative were estimated in vacuo, aprotic and protic solvents.Graphical abstractImage 1
       
  • Investigation of main group promoted carbon dioxide reduction
    • Abstract: Publication date: Available online 15 February 2019Source: TetrahedronAuthor(s): Brena L. Thompson, Zachariah M. Heiden The reduction of carbon dioxide (CO2) is of interest to the chemical industry, as many synthetic materials can be derived from CO2. To help determine the reagents needed for the functionalization of carbon dioxide this experimental and computational study describes the reduction of CO2 to formate and CO with hydride, electron, and proton sources in the presence of sterically bulky Lewis acids and bases. The insertion of carbon dioxide into a main group hydride, generating a main group formate, was computed to be more thermodynamically favorable for more hydridic (reducing) main group hydrides. A ten kcal/mol increase in hydricity (more reducing) of a main group hydride resulted in a 35% increase in the main group hydride's ability to insert CO2 into the main group hydride bond. The resulting main group formate exhibited a hydricity (reducing ability) about 10% less than the respective main group hydride prior to CO2 insertion. Coordination of a second identical Lewis acid to a main group formate complex further reduced the hydricity by about another 20%. The addition of electrons to the CO2 adduct of tBu3P and B(C6F5)3 resulted in converting the sequestered CO2 molecule to CO. Reduction of the CO2 adduct of tBu3P and B(C6F5)3 with both electrons and protons resulted in only proton reduction.Graphical abstractImage 1
       
  • Oxidative phenol-arene and phenol-phenol cross-coupling using periodic
           acid
    • Abstract: Publication date: Available online 13 February 2019Source: TetrahedronAuthor(s): Peng-Cheng Gao, Huan Chen, Vladimir Grigoryants, Qiang Zhang A simple, metal-free protocol for unsymmetrical biaryl coupling using H5IO6 is reported. H5IO6 was evaluated for a novel application in the oxidative cross-coupling of phenol-arene, phenol-phenol, and phenol-naphthol compounds. In this work, most of the couplings were completed within 30 min at ambient temperature. 30 coupling products were conveniently obtained using only 0.5 equivalent of H5IO6 in HFIP. A mechanism by which the transformation occurs is proposed.Graphical abstractImage 1
       
  • Novel coumarin-based containing denrons selective fluorescent chemosesor
           for sequential recognition of Cu2+ and PPi
    • Abstract: Publication date: Available online 13 February 2019Source: TetrahedronAuthor(s): Chongyang Zhao, Jian Chen, Duanlin Cao, Jianlong Wang, Wenbing Ma In this study, we have successfully synthesized a novel coumarin-based dendrons derivative CD and its chemical structure was characterized by 1H NMR, 13C NMR and ESI-HR-MS. The sensor CD showed an obvious “on-off” fluorescence quenching response toward Cu2+ with a maximum quenching efficiency of 99.8%. The CD-Cu2+ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions. The detection limit of the sensor CD was 0.29 × 10−6 M to Cu2+ and 2.39 × 10−9 M to PPi. In addition, the sensor CD showed a 1:1 binding stoichiometry to Cu2+ and the sensor CD-Cu2+ showed a 2:1 binding stoichiometry to PPi in CH3CN/HEPES buffer medium (9:1 v/v, pH = 7.2). The stable pH range of sensor CD to Cu2+ and CD-Cu2+ to PPi was from 3 to 8.Graphical abstractImage 1
       
  • Metal-free synthesis of benzimidazo[1,2-c]quinazolin-6-ones with indole
           and benzenediamine oxidized by I2/TBHP
    • Abstract: Publication date: Available online 13 February 2019Source: TetrahedronAuthor(s): Zhen Dai, Songhua Li, Yunyi Li, Lei Feng, Chen Ma A variety of benzimidazo[1,2-c]quinazolin-6-ones derivatives can be accessed in moderate to good yields under simple and metal-free reaction conditions using indoles and o-benzenediamines oxidized by iodine and TBHP. This procedure works in reasonable yields for different indoles as well as o-benzenediamines thus may provide a good synthesis of quinazolinones. A TBHP oxidized ring expansion reaction mechanism that explains the synthesis of benzimidazo[1,2-c]quinazolin-6-ones were reported.Graphical abstractImage 1
       
  • Synthesis of symmetrical biaryl compounds by homocoupling reaction
    • Abstract: Publication date: Available online 12 February 2019Source: TetrahedronAuthor(s): Stanley N.S. Vasconcelos, Joel S. Reis, Isadora M. de Oliveira, Michael N. Balfour, Hélio A. Stefani Since the development of the Ullmann coupling in the early 20th Century, there has been intense and continuous research on the syntheses of biaryl compounds, which appears as an interesting branch of organic chemistry.A myriad of methodologies for the synthesis of biaryl compounds have been studied and well established, including homocoupling methodologies, which in general are robust as well as consolidated strategies. Biaryl systems are quite relevant building blocks for the synthesis of more complex chemical structures. Besides the diversity of functional groups that can be used to promote a new aryl-aryl bond, there is a wide variety of transition metals that can act as catalyst in these processes.In this review, we summarized numerous methodologies of homocoupling reactions for the synthesis of symmetrical biaryl compounds.
       
  • Synthetic studies toward melotenine A
    • Abstract: Publication date: Available online 19 December 2018Source: TetrahedronAuthor(s): Ji-Yuan Du, Xian-Tao An, Xian-He Zhao, Xiao-Yan Ma, Ye-Xing Cao, Chun-An Fan Attempts to the construction of B/C ring and E ring in melotenine A are described. Based on para-dienone chemistry, a tactical application of tandem aminolysis/aza-Michael addition reaction was made to access highly functionalized building blocks with the pyrrolo[2,3-d]carbazole tetracyclic unit (A/B/C/D ring). Albeit negative results for assembling the dihydroazepine unit (E ring) by using the proposed fragmentation reaction of gem-dihalocyclopropanes, an alternative strategy based on ring closing metathesis was evolved to forge the E ring possessing a twisted 1,3-diene unit embedded in the rigid skeleton of melotenine A.Graphical abstractImage 1
       
  • Silica gel enables Achmatowicz rearrangement with KBr/oxone under
           “anhydrous” condition for one-pot functionalization
    • Abstract: Publication date: Available online 18 December 2018Source: TetrahedronAuthor(s): Guodong Zhao, Rongbiao Tong Silica gel was found to effectively promote Achmatowicz rearrangement (AchR) using KBr/oxone under near anhydrous condition. This new protocol allows direct functionalization of AchR products in a one-pot manner, effectively reducing the cost, time, and environmental impacts derived from the conventional stop-and-go approach using separate reaction vessels. These advantages were demonstrated in four types of sequential one-pot reactions: i) AchR-Kishi reduction (and AchR-Ferrier allylation); ii) AchR-acylation-O-glycosylation; iii) AchR-acylation-[5 + 2]-cycloaddition; and iv) AchR-TEMPO oxidation.Graphical abstractImage 1
       
  • Visible light induced C-H monofluoroalkylation to synthesize
           1,4-unsaturated compound
    • Abstract: Publication date: Available online 17 December 2018Source: TetrahedronAuthor(s): Wei-peng Li, Yu-cheng Zhu, Yan-jun Zhou, Hong-wei Yang, Cheng-jian Zhu We developed a method to synthesize fluorinated 1,4-unsaturated dicarbonyl compounds via photoredox catalyzed radical addition process. Commercially available ethyl bromodifluoroacetate (BrCF2CO2Et) as fluoroalkyl source, the corresponding fluoro-containing dicarbonyl compounds could be obtained in moderate to good yields.Graphical abstractImage 1
       
  • Stereoselectivity in a nitroso-ene cyclization: Formal synthesis of
           rac-manzacidins A and C
    • Abstract: Publication date: Available online 17 December 2018Source: TetrahedronAuthor(s): Ying Liu, Zhuwei Ruan, Yan Wang, Sha-Hua Huang, Ran Hong Nitroso-ene (NE) reactions have been adapted in the construction of nitrogen-containing motifs in many biologically interesting compounds. The transient and highly reactive “nitroso” species remains a challenge for designing stereocontrolled syntheses. Although chiral auxiliary-based method has been developed to achieve high diastereoselectivity, the use of the inherent chirality of the nitroso compound for stereochemical control remains underdeveloped. We chose the formation of a γ-lactam via a NE cyclization as a basis to study the applicable principles for future asymmetric syntheses. The selected examples presented herein reveal that the intramolecular hydrogen bond would provide conformational restraint to facilitate excellent facial selectivity in the NE reaction via a chair-like transition state. The sterically bulky amino group also provides excellent stereochemical control possibly through steric repulsion. The following transformations led to a key intermediate (Ohfune's lactone) in the preparation of manzacidins A and C and thus constitutes a formal synthesis.Graphical abstractImage 1
       
  • Visible-light-induced carbosulfonylation of unactivated alkenes via remote
           heteroaryl and oximino migration
    • Abstract: Publication date: Available online 7 December 2018Source: TetrahedronAuthor(s): Nana Tang, Shan Yang, Xinxin Wu, Chen Zhu An efficient visible-light photocatalytic protocol for the vicinal heteroarylsulfonylation and oximinosulfonylation of unactivated olefins is described. The addition of sulfonyl radicals to alkenes triggers the intramolecular migration of remote heteroaryl and oximino groups via CC bond cleavage. The transformation features a good functional group tolerance and a broad substrate scope. A variety of valuable heteroaryl- and oximino-substituted alkyl sulfones are obtained under mild conditions in synthetically useful yields.Graphical abstractImage 1
       
  • Copper-catalyzed asymmetric silylative cyclization of
           cyclohexadienone-containing 1,6-enynes
    • Abstract: Publication date: Available online 7 December 2018Source: TetrahedronAuthor(s): Cheng-Yu He, Li-Bo Xie, Rui Ding, Ping Tian, Guo-Qiang Lin The first copper-catalyzed asymmetric silylative cyclization of cyclohexadienone-containing 1,6-enynes has been accomplished through a tandem process: regioselective silylcupration of terminal unactivated alkynes and subsequently enantioselective conjugate addition to cyclohexadienones. This reaction proceeded smoothly to afford the cis-hydrobenzofuran and cis-hydroindole frameworks bearing two consecutive chiral carbon centers in high to excellent yields and moderate enantioselectivities. Additionally, the cyclization products could be readily subjected to several transformations for elaborating synthetic utilities.Graphical abstractImage 1
       
  • Catalytic asymmetric borylative aldol reaction of
           5,6-dihydro-2H-pyran-2-one and ketones
    • Abstract: Publication date: Available online 6 December 2018Source: TetrahedronAuthor(s): Qi Zhang, Xueshun Jia, Liang Yin A copper(I)-catalyzed asymmetric borylative aldol reaction of 5,6-dihydro-2H-pyran-2-one and simple ketones (including aromatic ketones and an aliphatic ketone) was disclosed, which afforded a series of chiral diols after an oxidative work-up in moderate yields with moderate to high diastereoselectivity and excellent enantioselectivity. The lactone moiety was easily opened with methanol to generate a chiral triol in moderate yield.Graphical abstractImage 1
       
  • Construction of multifunctional heterocycles bearing aza-quaternary
           carbons by titanocene-catalyzed umpolung reactions
    • Abstract: Publication date: Available online 5 December 2018Source: TetrahedronAuthor(s): Jiang-Tao Cheng, Xiao Zheng, Pei-Qiang Huang The combined application of Grignard/Reformatsky addition and the titanocene-catalyzed umpolung α-amino carbon-carbon bond formations provided a flexible and versatile protocol for preparation of multifunctional pyrrolidinones/piperidinones/N-Boc-piperidines bearing aza-quaternary carbons (AQC) from cyclic imides and analogues. Based on these multifunctional single-ring motifs, several advanced AQC-bearing heterocycles, such as AQC-possessing indolizidines and 1-azaspirocycles, have been constructed efficiently.Graphical abstractImage 1
       
  • Alkaloids from the roots of Stemona tuberosa and their
           anti-tobacco mosaic virus activities
    • Abstract: Publication date: Available online 5 December 2018Source: TetrahedronAuthor(s): Zhan-Xing Hu, Hong-Yu Tang, Jie Guo, Haji Aker Aisa, Yu Zhang, Xiao-Jiang Hao Stemtuberlines A (1) and B (2), two new alkaloids with a unique tricyclic pyrrolo [3,2,1-jk]benzazepine-12-one nucleus, three new croomine-type alkaloids, stemtuberlines C-E (3–5), together with seven known ones were isolated from the roots of Stemona tuberosa. The structures of the new alkaloids were elucidated based on a comprehensive spectroscopic data analysis. The absolute configurations of 1 and 2 were determined by quantum ECD calculations. The anti-tobacco mosaic virus activity of the Stemona alkaloids was firstly evaluated and compound 11 exhibited significant anti-tobacco mosaic virus activity with the curative inhibition rate of 84.6% at concentration of 50 μg/mL.Graphical abstractImage 1
       
  • A Garratt-Braverman cyclization route towards the synthesis of
           phenanthridine derivatives and their DNA-binding studies
    • Abstract: Publication date: Available online 11 February 2019Source: TetrahedronAuthor(s): Arundhoti Mandal, Prabuddha Bhattacharya, Amit K. Das, Amit Basak Garratt-Braverman cyclization has been employed to synthesize a series of dihydroisofuran fused phenanthridine derivatives. The established protocol proposes a simpler synthetic alternative to have access to these therapeutically relevant cytotoxic scaffolds. Single crystal X-ray data unambiguously confirmed the structures of the synthesized phenanthridine derivatives. UV–Vis absorption titration with calf-thymus DNA followed by fluorescence-based competitive ethidium bromide displacement assay established the synthesized target compounds as potent DNA-intercalating agents with intrinsic binding constant of the range 103-105. Results obtained from the molecular docking further justified the spectroscopically obtained results.Graphical abstractImage 1
       
  • Synthesis and utility of the natural type of porphyrin selectively labeled
           with Carbon-13 at α-meso site
    • Abstract: Publication date: Available online 11 February 2019Source: TetrahedronAuthor(s): Akira Ikezaki, Mikio Nakamura, Saburo Neya A concise synthesis of the 2,4-dimethyldeuteroporphyrin regiospecifically labeled with 13C at the α-meso site was developed. The starting material of ethyl 3,4,5-trimethylpyrrole-2-carboxylate was first converted to a 13C-labeled 5,5′-dimethyldipyrromethene with 13C formic acid, and the resulting dipyrromethene was coupled with 5,5′-dibromodipyrromethene to afford the 13C-labeled porphyrin in 26% yield. The paramagnetic 13C NMR measurements of myoglobin with the inversion-recovery method allowed us to detect selectively the α-meso-carbon signal of the iron complex. The heme is symmetric about the α,γ-meso carbon axis to prevent the orientational disorder in protein pocket. These results indicate that the 13C-enriched 2,4-dimethyldeuteroporphyrin is a new promising tool to elucidate the structure-function relationship of many hemoproteins.Graphical abstractImage 1
       
  • Ultrasensitive sensing of hydrazine vapor at sub-ppm level with
           pyrimidine-substituted perylene diimide film device
    • Abstract: Publication date: Available online 11 February 2019Source: TetrahedronAuthor(s): Hongliang Liu, Hailong Wang, Gang Liu, Shouzhi Pu, Haiquan Zhang A pyrimidine-substituted perylene diimide (Pyrimidine-PDI), in which the electron-deficient N-heterocyclic pyrimidine rings were introduced into the core positions, were synthesized to produce a conductometric film device for the sensitive detection of hydrazine (NH2NH2) vapor at room temperature under ambient conditions. The Pyrimidine-PDI film device exhibited ultrafast response, excellent reproducibility, excellent selectivity and good long-term stability towards hydrazine vapor. The response and recovery time of the device was calculated to be very low as 0.4 s and 0.6 s for hydrazine vapor at sub-ppm level (0.1 ppm). Moreover, the effect of the film thickness, relative humidity and temperature on the sensing performance were also studied. To understand the sensing mechanism, the core-benzene group perylene diimide (Ph-PDI) was also designed as a comparison. The film devices of Pyrimidine-PDI and Ph-PDI to hydrazine vapor were investigated with UV–vis spectra and cyclic voltammetry, which indicated that the redox of PDIs played a critical role in the sensing process. The electrochemical properties also indicated that electron-deficient N-heterocyclic pyrimidine rings could effectively lower the LUMO energy level and improve the response of the device.Graphical abstractImage 1
       
  • Bile acid based receptors for multiple metal ion recognition
    • Abstract: Publication date: Available online 10 February 2019Source: TetrahedronAuthor(s): Aradhana Nayal, Pradeep Kumar Muwal, Pramod S. Pandey A series of bile acid based receptors having triazole unit along with some additional heteroatom containing moieties as coordinating units for transition metal ion recognition has been synthesized. The UV–Vis studies revealed that these receptors show significant multiple binding affinity for Hg2+, Cd2+, Pb2+ and Cu2+ ions.Graphical abstractImage 1
       
  • Recent advances in indoline synthesis
    • Abstract: Publication date: Available online 10 February 2019Source: TetrahedronAuthor(s): Thiago S. Silva, Manoel T. Rodrigues, Hugo Santos, Lucas A. Zeoly, Wanda P. Almeida, Rosimeire C. Barcelos, Ralph C. Gomes, Fábio S. Fernandes, Fernando Coelho Indoline is an important structural motif present in several biologically active compounds from both natural and synthetic origins. The occurrence of this heterocyclic unity in these compounds is closely related to the biological activities they exhibit. This fact stimulated efforts that have been made worldwide to develop new synthetic approaches to prepare indolines. In this paper we reviewed critically the methods for indoline synthesis developed in the last years (from 2010 to 2018).Graphical abstractImage 1
       
  • Synthetic study of a moss-produced oxylipin and its structural revision
    • Abstract: Publication date: Available online 10 February 2019Source: TetrahedronAuthor(s): Hiroki Soeda, Ryo Towada, Yusuke Ogura, Tomoyo Mohri, Georg Pohnert, Shigefumi Kuwahara The proposed structure for a moss-produced acetylenic oxylipin (10-keto-type structure) was synthesized from a known glycidol derivative by an 11-step sequence involving epoxide ring opening with a terminal acetylene and enzymatic hydrolysis of a methyl ester intermediate. The NMR spectra of the proposed structure was, however, differrent from those of the natural oxylipin, which prompted us to synthesize its 9-epi-isomer and two diastereomeric 12-keto-type positional isomers. Comparison of the NMR spectra of the three isomers with those of the natural oxylipin indicated that the natural oxylipin was actually a mixture of the two diastereomeric positional isomers.Graphical abstractImage 1
       
  • DFT characterization of the mechanism for Staudinger/Aza-Wittig tandem
           organocatalysis
    • Abstract: Publication date: Available online 10 February 2019Source: TetrahedronAuthor(s): Mauro Fianchini, Feliu Maseras A computational simulation with DFT calculations and microkinetic modeling is carried out on a complete catalytic cycle, involving Staudinger ligation, aza-Wittig condensation and phosphine oxide recycle, for non-truncated substrates and catalyst. The Staudinger reaction produces phosphazenes (R3P = NR), also known as iminophosphoranes, from phosphines and organic azides. Electrophilic carbonyl groups react with phospazenes to produce imines and phosphine oxides. Recently the Staudinger reaction and the aza-Wittig condensation have been combined to spawn intramolecular tandems producing cyclic molecules of great pharmaceutical interest (e.g. benzoxazoles). The release of diatomic nitrogen combined with the formation of phosphine oxide represents the driving force of the reaction. The implementation of in situ recycling of the exhausted phosphine oxide into the Staudinger/aza-Wittig tandem improves the scopes and the applicability of the reaction, transforming it into a powerful and versatile synthetic tool.Graphical abstractImage 1
       
  • Borane/silane frustrated Lewis pairs for polymerization of β-substituted
           Michael acceptors
    • Abstract: Publication date: Available online 10 February 2019Source: TetrahedronAuthor(s): Michael L. McGraw, Eugene Y.-X. Chen Frustrated Lewis pairs (FLPs) of Lewis acid (LA) B(C6F5)3 and Lewis base hydrosilane [SiH] have been utilized to promote controlled polymerization of a challenging β-substituted Michael acceptor, methyl crotonate (MC), devoid of chain transfer side reactions. Mechanistic studies show that chain initiation involves LA-catalyzed 1,4-hydrosilylation of MC with [SiH] via FLP-type activation, generating a silyl ketene acetal nucleophile that participates in chain propagation via classic LA activation of monomer and a bimolecular conjugate addition mechanism. The role of the LA is conflicting in the two different catalytic cycles: the FLP activation in chain initiation requires LA-substrate (monomer) dissociation (or weak interaction) while the classic LA activation in chain propagation demands LA-monomer association (or strong interaction).Graphical abstractImage 1
       
  • Graphical abstract TOC
    • Abstract: Publication date: 1 March 2019Source: Tetrahedron, Volume 75, Issue 9Author(s):
       
  • Graphical abstract TOC
    • Abstract: Publication date: 1 March 2019Source: Tetrahedron, Volume 75, Issue 9Author(s):
       
  • Graphical abstract TOC cont'd
    • Abstract: Publication date: 1 March 2019Source: Tetrahedron, Volume 75, Issue 9Author(s):
       
  • Synthesis of N-Substituted phosphoramidic acid esters as “reverse”
           fosmidomycin analogues
    • Abstract: Publication date: Available online 8 February 2019Source: TetrahedronAuthor(s): Christiana M. Adeyemi, Heinrich C. Hoppe, Michelle Isaacs, Rosalyn Klein, Kevin A. Lobb, Perry T. Kaye An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.Graphical abstractImage 1
       
  • What to sacrifice' Fusions of cofactor regenerating enzymes with
           Baeyer-Villiger monooxygenases and alcohol dehydrogenases for
           self-sufficient redox biocatalysis
    • Abstract: Publication date: Available online 8 February 2019Source: TetrahedronAuthor(s): Ángela Mourelle-Insua, Friso S. Aalbers, Iván Lavandera, Vicente Gotor-Fernández, Marco W. Fraaije A collection of fusion biocatalysts has been generated that can be used for self-sufficient oxygenations or ketone reductions. These biocatalysts were created by fusing a Baeyer-Villiger monooxygenase (cyclohexanone monooxygenase from Thermocrispum municipale: TmCHMO) or an alcohol dehydrogenase (alcohol dehydrogenase from Lactobacillus brevis: LbADH) with three different cofactor regeneration enzymes (formate dehydrogenase from Burkholderia stabilis: BsFDH; glucose dehydrogenase from Sulfolobus tokodaii: StGDH, and phosphite dehydrogenase from Pseudomonas stutzeri: PsPTDH). Their tolerance against various organic solvents, including a deep eutectic solvent, and their activity and selectivity with a variety of substrates have been studied. Excellent conversions and enantioselectivities were obtained, demonstrating that these engineered fusion enzymes can be used as biocatalysts for the synthesis of (chiral) valuable compounds.Graphical abstractImage 1
       
  • Lewis acid base adducts of zwitterionic alkali metal methanides and
           silanides with BH3
    • Abstract: Publication date: Available online 7 February 2019Source: TetrahedronAuthor(s): Vidura D. Thalangamaarachchige, Nadeesha J. Silva, Daniel K. Unruh, Adelia J.A. Aquino, Clemens Krempner The synthesis, structures and spectroscopic properties of M(MeOCH2CH2OMe2Si)3CBH3 (M-1-BH3) and M(MeOCH2CH2OMe2Si)3SiBH3 (M-2-BH3) (M = Li, Na, K) derived from reactions of BH3 with the alkali metal zwitterions [M(MeOCH2CH2OMe2Si)3C] (M-1) and [M(MeOCH2CH2OMe2Si)3Si] (M-2) (M = Li, Na, K), resp., are reported. X-ray analysis and DFT calculations reveal discrete zwitterionic structures with the octahedral alkali metal cations rigidly locked and charge separated from the BH3 units via pendant donors groups. Solution experiments with the hydride acceptors B(C6F5)3 and [Ph3C]2[B12C12] indicate that Na-1-BH3 and can donate hydrides to form cations of formula [Na(MeOCH2CH2OMe2Si)3CBH2]+.Graphical abstractImage 1
       
  • Evaluating continuous chirality measure as a 3D descriptor in
           chemoinformatics applied to asymmetric catalysis
    • Abstract: Publication date: Available online 6 February 2019Source: TetrahedronAuthor(s): Andrew F. Zahrt, Scott E. Denmark Continuous Chirality Measure (CCM) is a computational metric by which to quantify the chirality of a compound. In enantioselective catalysis, prior work has postulated that CCM is correlated to selectivity and can be used to understand which structural features dictate catalyst efficacy. Herein, the investigation of CCM as a metric capable of guiding catalyst optimization is explored. Conformer-dependent CCM is also explored. Finally, CCM is used with Sterimol parameters to significantly improve the performance of Random Forest models.Graphical abstractImage 1
       
  • Oxidative ring-opening of isatins for the synthesis of 2-aminobenzamides
           and 2-aminobenzoates
    • Abstract: Publication date: Available online 6 February 2019Source: TetrahedronAuthor(s): Yu-Wei Wang, Lei Zheng, Feng-Cheng Jia, Yun-Feng Chen, An-Xin Wu An efficient and practical isatin-based oxidative domino protocol has been developed for the facile synthesis of 2-aminobenzamides and 2-aminobenzoates. The robust nature of this reaction system is reflected by accessible starting materials, room temperature and high-yield gram-scale synthesis.Graphical abstractImage 1
       
  • Benchmarking of laboratory evolved unspecific peroxygenases for the
           synthesis of human drug metabolites
    • Abstract: Publication date: Available online 6 February 2019Source: TetrahedronAuthor(s): Patricia Gomez de Santos, Fadia V. Cervantes, Florian Tieves, Francisco J. Plou, Frank Hollmann, Miguel Alcalde By mimicking the role of human liver P450 monooxygenases, fungal unspecific peroxygenases (UPOs) can perform a range of highly selective oxyfunctionalization reactions on pharmacological compounds, including O-dealkylations and hydroxylations, thereby simulating drug metabolism. Here we have benchmarked human drug metabolite (HDM) synthesis by several evolved UPO mutants, focusing on dextromethorphan, naproxen and tolbutamide. The HDM from dextromethorphan was prepared at the semi-preparative scale as a proof of production. The structural analysis of mutations involved in the synthesis of HDMs highlights the heme access channel as the main feature on which to focus when designing evolved UPOs. These variants are becoming emergent tools for the cost-effective synthesis of HDMs from next-generation drugs.Graphical abstractImage 1
       
  • Novel multi-responsive fluorescence switch for Hg2+ and UV/vis lights
           based on diarylethene-rhodamine derivative
    • Abstract: Publication date: Available online 5 February 2019Source: TetrahedronAuthor(s): Shuai Wang, Haichang Ding, Yuesong Wang, Congbin Fan, Gang Liu, Shouzhi Pu A new multi-responsive fluorescent switch DTE-Pip-Rho 1O has been designed and synthesized in this study. For this molecule, the reactive site of spirolactam ring is far away from the diarylethene unit through the intramolecular piperazine. It exhibited high selectivity and sensitivity to Hg2+ in addition to obvious color change (colorless-pink) and fluorescence “off-on” (dark-orange) during this process. It is believed that the color change is due to Hg2+-assisted hydrolysis of rhodamine hydrazide. Therefore, the new molecule can be used as colorimentric and fluorescent chemosensor for Hg2+ with high selectivity. The detection limits of absorbance and fluorescence for Hg2+ were calculated to be 1.15 μM and 1.16 μM, respectively. The resulting DTE-Pip-Rho 1O-Hg2+ could also function as a reversible fluorescence photo-switch in response to UV/vis light owing to FRET mechanism. Moreover, it has been demonstrated that the photo-switchable system displayed excellent fatigue resistance and remarkable anti-photobleaching capability.Graphical abstractA new multi-responsive diarylethene-based fluorescence switching system by using rhodamine as a fluorophore and the piperazine as the linker group was designed and synthesized, and its sensing behaviors for detecting Hg2+ and photo-switchable fluorescence were studied systematically.Image 1
       
  • Separation of cellulose/hemicellulose from lignin in white pine sawdust
           using boron trihalide reagents
    • Abstract: Publication date: Available online 5 February 2019Source: TetrahedronAuthor(s): M. Zain H. Kazmi, Abhoy Karmakar, Vladimir K. Michaelis, Florence J. Williams A mild method for the separation of cellulose/hemicellulose from extractive free sawdust is described. Sequential treatments with an equimolar mixture of BCl3 and BBr3 remove polysaccharide components from a white pine sawdust sample. Spectroscopic analyses, including solution and solid state NMR spectroscopy, confirm a reduction in the amount of aliphatic sugars in solid samples and show that extracted components consist only of polymeric sugars and are free of aromatics. Staining with fluorescent and colorimetric dyes confirm that the sawdust sample after boron trihalide treatment is primarily lignin, with no detectable polysaccharides.Graphical abstractImage 1
       
  • Is the term “Carbene” justified for remote N-heterocyclic carbenes
           (r-NHCs) and abnormal N-heterocyclic carbenes (aNHCs/MICs)'
    • Abstract: Publication date: Available online 4 February 2019Source: TetrahedronAuthor(s): Erich Kleinpeter, Andreas Koch The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of typical N-heterocyclic carbenes NHCs, r-NHCs, a-NHCs and MICs have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. Prior to that both structures and 13C chemical shifts were calculated and in case of isolated carbenes the computed δ(13C)/ppm values compared (as a quality criterion for obtained structures) with the experimental ones. The TSNMRS values of the studied carbenes, which are in mesomeric equilibrium with zwitterionic (ylide/betaine/mesoionic) resonance contributors, are employed to qualify and quantify the present electronic structure and if the term carbene is still justified to denote the compounds studied. The results, thus obtained from spatial magnetic properties (TSNMRS), are compared with the geometry of the compounds, the corresponding WIBERG's bond index values, and the 13C chemical shifts especially of the carbene electron-deficient centre.Graphical abstractImage 1
       
  • Exploration of the site-specific nature and generalizability of a
           trimethylammonium salt modification on vancomycin: A-ring derivatives
    • Abstract: Publication date: Available online 4 February 2019Source: TetrahedronAuthor(s): Zhi-Chen Wu, Dale L. Boger Vancomycin analogues bearing an A-ring trimethylammonium salt modification were synthesized and their antimicrobial activity against vancomycin-resistant Enterococci (VRE) was evaluated. The modification increased antimicrobial potency and provided the capability to induce bacteria cell membrane permeabilization, but both properties were weaker than that found with our earlier reported similar C-terminus modification. The results provide further insights on the additive effect and generalizability of the structural and site-specific nature of a peripheral quaternary trimethylammonium salt modification of vancomycin.Graphical abstractImage 1
       
  • H+alkoxylation+of+1-naphthylamine+derivatives+with+alcohols&rft.title=Tetrahedron&rft.issn=0040-4020&rft.date=&rft.volume=">Cobalt(II)–catalyzed C8H alkoxylation of 1-naphthylamine derivatives
           with alcohols
    • Abstract: Publication date: Available online 4 February 2019Source: TetrahedronAuthor(s): Tingfang Zhang, Hongmei Zhu, Fan Yang, Yusheng Wu, Yangjie Wu An efficient protocol for cobalt (II)-catalyzed regioselective aryl C8H bond alkoxylation of 1-naphthylamine derivatives with readily available alcohols has been developed, demonstrating an efficient approach to 8-alkoxy-1-naphthylamine derivatives with good functional group tolerance. Note that the picolinamide moiety as a bidentate directing group may play a key role in this regioselective transformation.Graphical abstractAn efficient protocol for cobalt (II)-catalyzed regioselective aryl C8H bond alkoxylation of 1-naphthylamine derivatives with readily available alcohols has been developed, demonstrating an efficient approach to 8-alkoxy-1-naphthylamine derivatives with good functional group tolerance. Note that the picolinamide moiety as a bidentate directing group may play a key role in this regioselective transformation.Image 1
       
  • Reaction of a ruthenium B-carboranyl hydride complex and BH3(SMe2):
           Selective formation of a pincer-supported metallaborane LRu(B3H8)
    • Abstract: Publication date: Available online 4 February 2019Source: TetrahedronAuthor(s): Bennett J. Eleazer, Mark D. Smith, Dmitry V. Peryshkov Reaction of a boryl hydride pincer complex (POBOP)Ru(H)(PPh3) (POBOP = 1,7-OP(i-Pr)2-m-2-carboranyl) and BH3(SMe2) at 70 °C led to the selective formation of a pincer-supported metallaborane (POBOP)Ru(B3H8). Single crystal structure of (POBOP)Ru(B3H8) was determined. This complex features coordination of the carborane cluster through adjacent boryl and borane groups that impose significantly different trans-influence on the coordinated B3H8 fragment.Graphical abstractImage 1
       
  • Synthesis and biological evaluation of new dipicolylamine zinc chelators
           as metallo-β-lactamase inhibitors
    • Abstract: Publication date: Available online 2 February 2019Source: TetrahedronAuthor(s): Anthony Prandina, Sylvie Radix, Marc Le Borgne, Lars P. Jordheim, Zineb Bousfiha, Christopher Fröhlich, Hanna-Kirsti Schröder Leiros, Ørjan Samuelsen, Espen Frøvold, Pål Rongved, Ove Alexander Høgmoen Åstrand Antibiotics are key drugs in modern healthcare, especially in hospitals, where multiresistant bacteria resides and is a potential threat to human health. In the present work, a new series of adjuvants working synergistically with the carbapenem meropenem, in which a selective zinc-chelating agent was covalently linked to the small bacterial peptide D-Ala-D-Ala, was synthesized and tested against two VIM-2 and NDM-1 metallo-β-lactamases (MBLs). The nature of the linker was modified in a structure-activity relationship study. Compound 1i, having an ethyl piperidine linker, lowered the MIC of meropenem from 32 to 64 mg/L to 2 and 1–2 mg/L against VIM-2- and NDM-1-producing clinical isolates, respectively. The IC50 value of 1i against VIM-2 was 9.8 and 2.2 μM after 5 and 20 min, respectively. Compound 1i also showed intrinsic toxicity against three eukaryotic human tumoral cell lines between 50 and 120 μM.Graphical abstractImage 1
       
  • A novel rhodamine-based turn-on probe for fluorescent detection of Au3+
           and colorimetric detection of Cu2+
    • Abstract: Publication date: Available online 2 February 2019Source: TetrahedronAuthor(s): A. Yu. Mironenko, M.V. Tutov, A.K. Chepak, P.A. Zadorozhny, S. Yu. Bratskaya In this work, we design and synthesize the novel probe RC through introduction the 1-aza-4,13-dithia-15-crown-5 ring into the structure of rhodamine 6G hydrazide, where the N atom of crown ring is responsible for quenching of rhodamine fluorescence. The compound obtained behaves as multifunctional cation sensor providing selective fluorescent response to Au3+ and selective colorimetric response to Cu2+ ions in aqueous acetonitrile (1/1, v/v) at pH 7.0. The use of 10−5 M RC solution allowed reliable determination of target cations in the presence of a wide range of environmentally relevant ions with detection limits of 2 × 10−6 M and 5 × 10−7 M for gold and copper, respectively.Graphical abstractImage 1
       
  • I2-mediated and direct synthesis of 3-phenoxy imidazo
           heterocycles
    • Abstract: Publication date: Available online 2 February 2019Source: TetrahedronAuthor(s): Yanchun Guo, Yuexiu Wang, Han Xue, Shuxia Cao, Yufen Zhao An I2-mediated protocol was proposed for the synthesis of 3-phenoxy imidazo heterocycles from aromatic ketones and 2-aminopyridines or 2-aminobenzothiazole. This direct, efficient and operationally simple method provided a fundamentally novel and rapid approach for the synthesis of 3-phenoxy imidazo heterocycles with good to excellent yields, and it avoided the requirement of any metal, base and extra oxidant.Graphical abstractImage 1
       
  • New hydroperoxybriarane diterpenoids from the octocoral Briareum violaceum
    • Abstract: Publication date: Available online 2 February 2019Source: TetrahedronAuthor(s): Jia-Wen Yao, Wei-Chiung Chi, Jing-Hao Xu, Gene-Hsiang Lee, Michael Y. Chiang, Bo-Rong Peng, Nai-Cheng Lin, Chiung-Chin Hu, Lee-Shing Fang, Guo-Qiang Li, Yu-Chia Chang, Tsong-Long Hwang, Ping-Jyun Sung A known briarane, brianthein W (1), along with four new hydroperoxybriaranes, briaviolides R–U (2–5), have been obtained from the octocoral Briareum violaceum. The absolute configuration of 1 was determined by X-ray analysis for the first time and the structures of briaranes 2–5 were established by spectroscopic methods. Bioactivity study showed that briarane 3 decreased the production of superoxide anions from human neutrophils.Graphical abstractImage 1
       
  • Enantioselective sensing of carboxylic acids with a
           bis(urea)oligo(phenylene)ethynylene foldamer
    • Abstract: Publication date: Available online 2 February 2019Source: TetrahedronAuthor(s): Zeus A. De los Santos, Georgy Yusin, Christian Wolf The development of molecular probes for optical sensing of chiral compounds has received increasing attention in recent years, in particular because of the potential to accelerate asymmetric reaction analysis. In this study, we prepared conformationally flexible oligo(phenylene)ethynylene foldamers carrying peripheral bis(trifluoromethyl)phenylurea units that undergo hydrogen bonding with chiral carboxylic acids. This interaction results in a chiral amplification process across the stereodynamic sensor scaffold which coincides with characteristic circular dichroism signals at high wavelengths. The induced chiroptical signals allow quantitative determination of the enantiomeric excess of the substrate which was demonstrated with nonracemic samples of tartaric acid. The chirality sensing assay is fast, sufficiently accurate for high-throughput screening purposes and adaptable to parallel analysis with multiwell plate readers.Graphical abstractImage 1
       
  • Energising the E-factor: The E+-factor
    • Abstract: Publication date: Available online 31 January 2019Source: TetrahedronAuthor(s): Florian Tieves, Fabio Tonin, Elena Fernández-Fueyo, John M. Robbins, Bettina Bommarius, Andreas S. Bommarius, Miguel Alcalde, Frank Hollmann The E-factor has become an important measure for the environmental impact of (bio)chemical reactions. However, summing up the obvious wastes generated in the laboratory neglects energy-related wastes (mostly greenhouse gases) which are generated elsewhere. To estimate these wastes, we propose to extend the E-factor by an energy-term (E+-factor). At the example of a lab-scale enzyme fermentation, we demonstrate that the E+-factor can constitute a multiple of the classical E-factor and therefore must not be neglected striving for a holistic estimation of the environmental impact.Graphical abstractImage 1
       
  • Microbial transformation of laxogenin by the fungus Syncephalastrum
           racemosum
    • Abstract: Publication date: Available online 31 January 2019Source: TetrahedronAuthor(s): Yihai Wang, Limin Xiang, Yuying Huang, Xiaomin Yi, Xiangjiu He Biotransformation of laxogenin (LG, 1) was performed by the fungus Syncephalastrum racemosum (AS 3.264). Thirteen previously undescribed metabolites were obtained and their structures were elucidated by spectroscopic analysis. S. racemosum catalyzes mainly oxygenation reactions of the B, C, and D rings of the sapogenin to afford metabolites 2–12. Conversion of the spirostanol skeleton to cholestane-type was also encountered in metabolite 13. Rearrangement of F-ring afforded F-ring ‘furanose’ sapogenin was observed in metabolite 14. The substrate and its derivatives were evaluated for their anti-neuroinflammatory activities. LG and metabolites 2, 3, 5, 8–10 and 13–14 exhibited moderate to good inhibitory activities on lipopolysaccharide-induced NO (nitric oxide) production in BV-2 cells. Moreover, 1, 2 and 5 dose-dependently reduced the LPS-induced iNOS and COX-2 expressions.Graphical abstractImage 1
       
  • Diastereoselective multicomponent Amine-Aldehyde-Dienophile (AAD) process
           for the synthesis of polysubstituted cyclohex-2-enylamines
    • Abstract: Publication date: Available online 30 January 2019Source: TetrahedronAuthor(s): Verónica Selva, Ihssene Chabour, Carmen Nájera, José M. Sansano The multicomponent Amine-Aldehyde-Dienophile reaction is optimized employing benzyl or 4-methoxybenzylamine. The interest of the transformation consist in synthesis of polysubstituted cyclohex-2-enylamines. The study of the scope of this AAD process is carried out as well as the diastereoselective version employing commercially available chiral benzylic amines and a maleimide with the chiral information at the N-substituent. VCD spectroscopy is a very useful tool for the determination of the absolute configuration of the isolated enantiomerically enriched compounds.Graphical abstractImage 1
       
  • Preparation of a novel bromine complex and its application in organic
           synthesis
    • Abstract: Publication date: Available online 30 January 2019Source: TetrahedronAuthor(s): Yuya Nishio, Kotaro Yubata, Yutaro Wakai, Kotaro Notsu, Katsumi Yamamoto, Hideki Fujiwara, Hiroshi Matsubara Although molecular bromine (Br2) is a useful brominating reagent, it is not easy to handle. Herein, we describe the preparation of a novel air-stable bromine complex prepared from 1,3-dimethylimidazolidinone (DMI) and Br2, which was identified to be (DMI)2HBr3 by spectral and X-ray techniques. This complex was then used to brominate olefins, carbonyl compounds, and aromatics, as well as in the Hofmann rearrangement. Yields of reaction products using this complex were almost the same or superior to those using other bromine alternatives.Graphical abstractImage 1
       
  • Hydrophosphonylation of chiral hexahydroquinoxalin-2(1H)-one derivatives
           as an effective route to new bicyclic compounds: Aminophosphonates,
           enamines and imines
    • Abstract: Publication date: Available online 30 January 2019Source: TetrahedronAuthor(s): Jakub Iwanejko, Anna Brol, Bartłomiej Szyja, Marek Daszkiewicz, Elżbieta Wojaczyńska, Tomasz K. Olszewski A series of new aminophosphonate and phosphonic acid derivatives of hexahydroquinoxalin-2(1H)-ones and tetrahydroquinoxalin-2(1H)-ones were synthesised via hydrophosphonylation of the corresponding bicyclic imines with various dialkyl or diaryl H-phosphonates, H-phosphinates or H-phosphine oxides as phosphorus nucleophiles. The utility of the obtained compounds was demonstrated by their application as a source of phosphonate carbanion in the Horner-Wadsworth-Emmons (HWE) reaction leading to new bicyclic amines with an exocyclic, and unexpectedly, also endocyclic double bond depending on the structure of the aldehyde used.Graphical abstractImage 1
       
  • Copper-catalyzed three-component reaction of ethynylstibanes, organic
           azides, and selenium: A simple and efficient synthesis of novel selenides
           and diselenides having 1,2,3-triazole rings
    • Abstract: Publication date: Available online 29 January 2019Source: TetrahedronAuthor(s): Mizuki Yamada, Mio Matsumura, Erina Sakaki, Shih-yun Yen, Masatoshi Kawahata, Tadashi Hyodo, Kentaro Yamaguchi, Yuki Murata, Shuji Yasuike A simple method for the synthesis of monoselenides and diselenides having 1,2,3-triazole ring is described herein. The three component reaction of ethynylstibanes, organic azides, and selenium powder is catalyzed by CuI (10 mol%) using 1,10-phenanthroline as the ligand (10 mol%) under aerobic conditions. Either selenides or diselenides can be synthesized by selecting the appropriate amount of selenium powder for otherwise identical reaction conditions. The obtained selenides and diselenides having a 1,2,3-triazole ring are all novel compounds. By using an antimony reagent, this one-pot reaction provides regioselective double Se-arylation under simple reaction conditions.Graphical abstractImage 1
       
  • Chiral (cyclopentadienone)iron complexes with a stereogenic plane as
           pre-catalysts for the asymmetric hydrogenation of polar double bonds
    • Abstract: Publication date: Available online 29 January 2019Source: TetrahedronAuthor(s): Xishan Bai, Mattia Cettolin, Giulia Mazzoccanti, Marco Pierini, Umberto Piarulli, Valentina Colombo, Alberto Dal Corso, Luca Pignataro, Cesare GennariabstractIn this paper, we describe a small library of easy-to-prepare chiral (cyclopentadienone)iron pre-catalysts for enantioselective C=O and C=N hydrogenations. Starting from readily accessible achiral materials, six chiral (cyclopentadienone)iron complexes (1a-f) possessing a stereogenic plane were synthesized in racemic form. Based on the screening of pre-catalysts (±)-1a-f in the hydrogenation of ketones and ketimines, we selected two complexes (1a and 1d) for resolution by semipreparative enantioselective HPLC. The absolute configuration of the separated enantiomers of 1a and 1d was assigned by XRD analysis (1a) and by comparison between experimental and DFT-calculated ECD and ORD spectra (1d). The enantiopure pre-catalysts (S)-1a and (R)-1d were tested in the asymmetric hydrogenation of several ketones and ketimines and showed good activity and modest enantioselectivity, the e.e. values ranging from very low to moderate (54%).Graphical abstractImage 1
       
  • Synthesis of novel oil-soluble fluorinated surfactants via Wittig-Horner
           reaction
    • Abstract: Publication date: Available online 28 January 2019Source: TetrahedronAuthor(s): Ding Zhang, Min Sha, Ping Xing, Renming Pan, Xiangyang Lin, Biao Jiang In this paper, the synthesis and characterization of novel oil-soluble fluorinated surfactants were reported. Both Wittig and Wittig-Horner reaction were used for constructing the perfluorinated branch-chain structure, and the latter provided a better method through a three-step synthesis route which was easy worked up and low cost. The surface tension of novel products in toluene, n-hexane and nitromethane with concentrations of 0.1 mol/L, 0.05 mol/L, 0.025 mol/L, 0.0125 mol/L, 0.00625 mol/L and 0 mol/L were examined. The surface tension research of these surfactants showed that they can reduce the surface tension of organic reagents dramatically. For example, compound 1e can reduce the surface tension of nitromethane from 36.6 mN/m to 24.2 mN/m in the concentration of 0.1 mol/L, and the surface tension of toluene was reduced from 28.0 mN/m to 22.7 mN/m when the concentration of compound 1a was 0.1 mol/L.Graphical abstractImage 1
       
  • Fe(III)-Catalyzed direct C3 chalcogenylation of indole: The effect of
           iodide ions
    • Abstract: Publication date: Available online 28 January 2019Source: TetrahedronAuthor(s): Eduardo Q. Luz, Diego Seckler, Janylson Souza Araújo, Leonardo Angst, David B. Lima, Elise Ane Maluf Rios, Ronny R. Ribeiro, Daniel S. Rampon A mild and efficient iron (III)-catalyzed C3 chalcogenylation of indoles has been developed and the role of the iodide ions in this transformation was investigated. EPR experiments revealed the reduction of Fe(III) to Fe(II) under the reaction conditions, supporting the formation of molecular iodine in the system, which in effect catalyze the reaction. The scope of the chalcogenylation was broad and the synthesis of more functionalized 3-selenylindoles was explored.Graphical abstractImage 1
       
  • Palladium-catalyzed tandem cyclization of fluorinated imidoyl chlorides
           with 2- bromophenylboronic acid: Synthesis of
           6-fluoroalkyl-Phenanthridines
    • Abstract: Publication date: Available online 26 January 2019Source: TetrahedronAuthor(s): Yinwei Bao, Zhuo Wang, Chen Chen, Bolin Zhu, Yuebo Wang, Jinghui Zhao, Jinyu Gong, Mengya Han, Chang Liu An efficient method has been developed to synthesize 6-fluoroalkyl-phenanthridines via the palladium-catalyzed tandem cyclization of fluorinated imidoyl chlorides with 2-bromophenylboronic acid. This methodology facilitates the rapid synthesis of 6-fluoroalkyl-phenanthridines through dual C–C bond formation in an oxidant-free one-pot manner.Graphical abstractImage 1
       
  • Metal-free direct regioselective thiolation of imidazoheterocycles in
           water at room temperature
    • Abstract: Publication date: Available online 26 January 2019Source: TetrahedronAuthor(s): Dulin Kong, Qinghe Wang, Tiao Huang, Min Liang, Qiang Lin, Mingshu Wu A metal-free direct thiolation of imidazoheterocycles with various thiophenol in water at room temperature has been developed. In addition, the chemistry provides several advantages including mild condition, high yields, good functional group tolerance, green solvents and suitable for large-scale operations.Graphical abstractImage 1
       
  • Iron-catalyzed Minisci acylation of N-heteroarenes with
           α-keto acids
    • Abstract: Publication date: Available online 26 January 2019Source: TetrahedronAuthor(s): Xiu-Zhi Wang, Cheng-Chu Zeng An efficient and mild protocol has been developed for the Minisci acylation reactions of nitrogen-containing heteroarenes with α-keto acids. Distinct from the conventional Minisci acylation conditions, the chemistry was performed using non-noble metal Fe(II), instead of expensive Ag(I) salt, as catalyst. A wide range of substrates, including aliphatic or aromatic α-keto acids, as well as various N-heteroarenes, proved to be compatible with the protocol. Scale-up experiment also demonstrates the practicality of the approach.Graphical abstractImage 1
       
  • Synthesis of novel
           8-(het)aryl-6H-pyrano[4′,3′:4,5]thieno[3,2-b]pyridines by 6-endo-dig
           cyclization of Sonogashira products and halolactonizations with Cu
           salts/NXS. Preliminary antitumor evaluation
    • Abstract: Publication date: Available online 26 January 2019Source: TetrahedronAuthor(s): Juliana M. Rodrigues, Pierre Buisson, Joana M. Pereira, Inês M. Pinheiro, Tamara Fernández-Marcelo, M. Helena Vasconcelos, Sabine Berteina-Raboin, Maria-João R.P. Queiroz Novel 8-(het)aryl-6H-pyrano[4′,3′:4,5]thieno[3,2-b]pyridines were prepared in good to high yields by a tandem one-pot procedure of Sonogashira coupling and 6-endo-dig lactonization from 3-bromothieno[3,2-b]pyridine-2-carboxylic acid and (het)arylalkynes. Sonogashira coupling products were also prepared from the corresponding methyl ester giving in the same reaction the corresponding 6-endo-dig compounds as minor products. The Sonogashira phenyl ester product gave cyclization with electrophiles only in low to moderate yields. Nevertheless, halolactonizations using Cu(I) or (II) salts/N-halosuccinimides (NXS) from either the phenyl ester or the carboxylic acid derivatives occurred in good to high yields. The growth inhibition potential of the compounds was evaluated using human tumor cell lines, HCT-15 (colorectal adenocarcinoma) and NCI-H460 (non-small cell lung cancer) and studies of apoptosis induction were performed for the three most promising compounds in HCT-15 cells. Two of them caused almost 40% of cell death by apoptosis when tested at their 1.5 × GI50 concentrations. The tricyclic lactone with a F atom in the meta position showed to be the most promising one.Graphical abstractImage 1
       
  • Proline derivatives incorporating hydrophobic long-chain derived from
           natural and synthetic fatty acids
    • Abstract: Publication date: Available online 25 January 2019Source: TetrahedronAuthor(s): Elisabet Selva, J. Javier Soto, Carmen Nájera, Francisco Foubelo, José M. Sansano The α-hydrophobic long chain-α-amino esters are prepared by α-hydroxylation of a series of fatty acid esters [derived from oleic acid (OA), linolenic acid (LA), docosahexaenoic acid (DHA) and arachidonic acid (ARA)] followed by Mitsunobu reaction and hydrazinolysis of the phthalimide. These amino esters are mixed with aldehydes and electrophilic alkenes to give very good chemical yields and diastereoselectivities of prolinate derivatives incorporating a hydrophobic long chain at the α-position. This multicomponent 1,3-dipolar cycloaddition (1,3-DC) takes place at room temperature. The synthesis of the homologue hydrophobic chain of OA is performed by its oxidation to aldehyde/racemic N-tert-butylsulfinyl imine/Neff reaction. Final 1,3-DC with benzaldehyde and N-methylmaleimide affords homologue prolinate derivative in good yield.Graphical abstractImage 1
       
  • Synthesis of the H-phosphonate dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide
           and the phospha-Michael addition to unsaturated compounds
    • Abstract: Publication date: Available online 25 January 2019Source: TetrahedronAuthor(s): Johannes Lenz, Doris Pospiech, Hartmut Komber, Maxime Paven, Rolf Albach, Stamo Mentizi, Gerhard Langstein, Brigitte Voit A series of phosphonate-containing compounds based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) is presented. BPPO is synthesized by a three–component condensation and is added to activated alkenes with systematically varied structure via phospha-Michael addition. Acrylates, α,β-unsaturated carboxylic acid diesters and benzoquinone are used as activated alkenes. The new compounds are characterized by 1H, 13C and 31P NMR spectroscopy. The as-prepared phosphonates are envisioned to have flame retardant properties.Graphical abstractImage 1
       
  • Design and synthesis of fused cyclic sulfamides-oxazolidinones
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Hamdi Rmedi An efficient protocol for the synthesis of a new series of oxazolidin-2-ones containing sulfamide moieties is described. The synthesis was achieved in two reaction steps. The first was carried out under anhydrous conditions at 0 °C through a selective addition of an alcohol and primary amines to chlorosulfonylisocyanate to produce N-carboxylsulfamides in good yields. Under appropriate conditions of solvent, base and temperature, these intermediates underwent subsequent intramolecular cyclizations, giving exclusively the corresponding sulfamoyloxazolidinones.Graphical abstractImage 1
       
  • 14-Noreudesmanes and a phenylpropane heterodimer from sea buckthorn berry
           inhibit Herpes simplex type 2 virus replication
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Dóra Rédei, Norbert Kúsz, Tímea Rafai, Anita Bogdanov, Katalin Burián, Attila Csorba, Attila Mándi, Tibor Kurtán, Andrea Vasas, Judit Hohmann Two new 14-noreudesmane sesquiterpenes, one new phenylpropane heterodimer, caulilexin C, and uvaol were isolated from the 70% MeOH extract of the fruit peel of Elaeagnus rhamnoides. The structures of the compounds were elucidated by HRESIMS and advanced NMR methods. The absolute configuration of (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene was determined by the TDDFT-ECD method. The new compounds, together with structurally similar naphthalenes (musizin, musizin-8-O-glucoside, torachrysone-8-O-glucoside) and 1,4-naphthoquinone (2-methylstipandrone), isolated previously from Rumex aquaticus, were investigated for their antiviral activity against Herpes simplex virus type 2 (HSV-2) using two different methods. Applying the traditional virus yield reduction test, (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene, 1-[3-methoxy-4-(2-methoxy-4-(1E)-propenyl-phenoxy)-phenyl]-propane-1,2-diol, and musizin caused a 2.00 log10, 3.49 log10, and 2.33 log10 reduction of HSV-2 yield, respectively, at a concentration of 12.5 μM 2-Hydroxy-1-methoxy-6,9-dioxo-14-noreudesm-1,3,5(10),7-tetraene exhibited an antiviral effect at concentration of 50 μM only. Similar results were obtained when the qPCR method was used to test the antiviral activity of the compounds.Graphical abstractImage 1
       
  • Palladium-catalyzed Mizoroki-Heck reactions in water using
           thermoresponsive polymer micelles
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Noriyuki Suzuki, Taiga Takabe, Yoshiko Yamauchi, Shun Koyama, Rina Koike, Masahiro Rikukawa, Wei-Ting Liao, Wen-Sheng Peng, Fu-Yu Tsai Palladium-catalyzed Mizoroki-Heck reactions were carried out in water using thermoresponsive polymer micelles. The micelles were generated from thermoresponsive block copolymers consisting of a poly(N-isopropylacrylamide) (PNIPAAm) segment and a hydrophilic segment such as nonionic poly(ethylene glycol) (PEG) (2) and anionic poly(sodium p-styrenesulfonate) (PSSNa) (9). These copolymers exhibited lower critical solution temperature (LCST) behavior at ca. 40–50 °C and showed thermal stimuli-induced formation and dissociation of micelles. The copolymers formed micelles in aqueous solution at higher temperature, where catalytic reactions proceeded. At lower temperature, the micelles dissociated to form a clear solution, enabling efficient extraction of the products from aqueous reaction mixture. In the presence of these copolymers, palladium complexes catalyzed the coupling reactions between aryl iodides and alkene compounds inside the hydrophobic micelle cores in water under relatively milder conditions. Extraction of the products from the aqueous solution of 2 or 9 was found to be efficient enough in comparison with conventional surfactants.Graphical abstractImage 1
       
  • Reassigning the stereochemistry of bioactive cepharanthine using
           calculated versus experimental chiroptical spectroscopies
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Jie Ren, Dan Zhao, Shi-Jie Wu, Jie Wang, Yun-Jing Jia, Wen-Xin Li, Hua-Jie Zhu, Fei Cao, Wan Li, Charles U. Pittman, Xiang-Jiu He The absolute configuration of cepharanthine (1), a strongly bioactive bisbenzylisoquinoline alkaloid exhibiting 12 specific bioactivities without any reported negative side-effects, has been reassigned from (1R,1′S) to (1R,1′R) using quantum theory. The absolute configurations (ACs) of 13 other analogues of 1 were also systematically reassigned. Six quaternary salts were prepared from 1 and one exhibited strong anti-bacterial activity against Bacillus subtilis with MIC 0.31 μM, while Ciprofloxacin, the positive control medicine was 3.88 μM. This work established the critical importance of correlating chiroptical experimental spectra with their quantum mechanically predicted spectra for accurate stereogenic center assignments.Graphical abstractImage 1
       
  • Fusaspirols A-D, novel oxaspirol derivatives isolated from Fusarium
           solani
    B-18
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Nanang Rudianto Ariefta, Hasna Tazkia Nikmawahda, Takako Aboshi, Tetsuya Murayama, Keitaro Tawaraya, Takuya Koseki, Genta Katagi, Yoshito Kakihara, Yoshihito Shiono Four novel compounds with γ-methylidene-spirobutanolide core, fusaspirols A-D, were isolated from the brown rice culture of Fusarium solani B-18. Their structures were established by extensive spectroscopic analyses of 1D/2D-NMR, HRESITOFMS, and chemical derivatization. The absolute configurations of secondary alcohols in fusaspirols A and D were determined using modified Mosher's ester method. Fusaspirol A and 4,9-di-O-acetylfusaspirol A activated a signaling pathway in osteoclastic differentiation of murine macrophage derived RAW264.7 cells.Graphical abstractImage 1
       
  • Synthesis of C 3-Symmetric star-shaped molecules containing 1,3-azoles via
           hetero-aryl Heck coupling
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Sambasivarao Kotha, Saidulu Todeti We have demonstrated a useful synthetic strategy to assemble star-shaped C3-symmetric molecules containing 1,3-azole moieties at the periphery. To generate these C3-symmetric heterocycles, we have employed the Pd/Cu-based coupling reactions. To this end, we have used benzoxazole, benzothiazole and benzimidazole as coupling partners to generate the corresponding hetero-aryl Heck coupling products.Graphical abstractImage 1
       
  • The first example of a “click” reaction with a carboranyl
           azide and an olefin
    • Abstract: Publication date: Available online 24 January 2019Source: TetrahedronAuthor(s): Uday B. Chauhan, Anton W. Tomich, Vincent Lavallo While typical organic azides have long been known to undergo 1–3 dipolar cycloadditions with strained C-C multiple bonds, such chemistry has never been reported between organomimetic carboranyl azides and alkenes. Here we show that the carborane o-PhCN3CB10H10 readily undergoes cycloaddition with norbornene at ambient temperature to afford the corresponding triazole adduct with perfect exo-selectivity. The structure of the ensuing heterocycle was unambiguously determined by multinuclear NMR, correlation NMR, and single crystal X-ray diffraction experiments. This first example of such reactivity demonstrates a method to easily introduce carborane clusters directly to scaffolds of interest, without having an organic spacer between the azide functionality and cluster.Graphical abstractImage 1
       
  • The rotameric (R*,S*)- and (R*,R*)-biaryl-3,3′-diphthalides of
           polyphenylene series
    • Abstract: Publication date: Available online 23 January 2019Source: TetrahedronAuthor(s): Tagir A. Yangirov, Akhnef A. Fatykhov, Elvira A. Sedova, Leonard M. Khalilov, Ekaterina S. Meshcheryakova, Sergey P. Ivanov, Sergey N. Salazkin, Vladimir A. Kraikin A wide range of diastereomeric pairs of biaryl-3,3′-diphthalides with aromatic (heteroaromatic) substituents of polyphenylene series (including halogen substituted) was synthesized. All of them were separated and characterized by the methods of X-ray analysis, HPLC, IR-, 1H and 13C NMR spectroscopy. It was determined that solubility, tendency to adsorption and related to it retention times, chemical shifts of equivalent hydrogen and carbon atoms of biaryl-3,3′-diphthalides diastereoisomers are determined firstly by the stereo-electronic effects of two adjacent strongly polar phthalide groups. It was shown that both in crystalline phase and in solution all the diphthalides, regardless of the chemical structure of their substituents, are existing as stable rotamers with cis or synperiplanar (chiral forms) and trans or antiperiplanar (meso-forms) conformation.Graphical abstractImage 1
       
  • Carboxylic acid recognition of diamidine having a fluorescent
           1,8-diphenylanthracene unit and its detection of amidinium-carboxylate and
           amidinium formation
    • Abstract: Publication date: Available online 23 January 2019Source: TetrahedronAuthor(s): Takahiro Kusukawa, Hiroki Aramoto, Takehiro Umeda, Yusuke Kojima A diphenylanthracene-based diamidine (1a) fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized, which has an extended π-conjugation rather than a simple anthracene ring, in order to observe highly different fluorescence wavelengths after complex formation with dicarboxylic acids. The fluorescence spectra of the mixed solution of the diamidine 1a and carboxylic acids showed two different fluorescence bands, which corresponded to the complex formation (amidinium-carboxylate formation, λem = 450 nm, light blue color) and dissociated amidinium formation (λem = 510 nm as a broad band, green color). The complexed and dissociated states were confirmed by DOSY NMR and TD-DFT calculations. These different fluorescence wavelengths may come from the differences in the dihedral angles between the phenyl rings at the 1,8-position and anthracene ring (difference in π-conjugation) of 1a under complex formation and dissociated amidinium formation. The proposed mechanism for the observation of the different fluorescence wavelengths (complex formation and amidinium formation) was also confirmed by the fluorescence study of diamidine 1b which causes restricted rotation of the phenyl rings by substitution of the steric methyl groups, and observed the same fluorescence spectra for the complex formation and amidinium formation (400, 420, 450 nm as a vibrational structure of anthracene ring). These fluorescence characteristics of the diamidine 1a are also applicable for the detection of α,ω−dicarboxylic acids.Graphical abstractImage 1
       
  • Control of site selectivity in trifluoromethylation of alkenes bearing a
           pendant indolyl group: Synthesis of CF3-containing tetrahydrocarbazoles
    • Abstract: Publication date: Available online 23 January 2019Source: TetrahedronAuthor(s): Ryo Murakami, Daisuke Sekine, Yuma Aoki, Shintaro Kawamura, Mikiko Sodeoka We present a tetrahydrocarbozole-forming carbo-trifluoromethylation of indoles bearing an alkenyl group at the C3 position. The reaction proceeded selectively with the combination of TsOH·H2O as a catalyst and CH2Cl2 as a solvent. The site-selectivity could be altered by changing the reaction solvent; the use of THF instead of CH2Cl2 increased the formation of aromatic trifluoromethylation products.Graphical abstractImage 1
       
  • 5-Norbornene-2-carboxylic acid: Another catalytic mediator for
           Catellani-type reactions
    • Abstract: Publication date: Available online 22 January 2019Source: TetrahedronAuthor(s): Ze-Shui Liu, Guangyin Qian, Qianwen Gao, Peng Wang, Hong-Gang Cheng, Yu Hua, Qianghui Zhou Mediators play a central role in Catellani-type reactions. Herein we reported the discovery of inexpensive 5-norbornene-2-carboxylic acid (N4) as a general catalytic mediator (20 mol%) to facilitate ortho C−H activation and the following C−C bond formation of aryl iodides. Firstly, a cooperative catalytic system comprising N4 and a palladium/XPhos complex was developed for the novel Catellani/redox-relay Heck cascade to construct tetrahydronaphthalenes and indanes that contain a quaternary carbon stereogenic center. The striking feature of this work was the avoidance of stoichiometric NBE mediator that are usually required for Catellani-type reactions. Then, preliminary results demonstrated that N4 could act as a general catalytic mediator to replace NBE for other Catellani-type reactions, which will undoubtedly inspire future developments in the field of cooperative catalysis. Finally, control experiments indicated that the carboxylic acid moiety of N4 plays an essential role in its ability to serve as a superior mediator.Graphical abstractImage 1
       
  • Antiproliferative effects of zerumbone-pendant derivatives on human T-cell
           lymphoid cell line Jurkat cells
    • Abstract: Publication date: Available online 22 January 2019Source: TetrahedronAuthor(s): Yoshimi Utaka, Gengo Kashiwazaki, Sachiko Tajima, Yuko Fujiwara, Keitaro Sumi, Tomohiro Itoh, Takashi Kitayama Zerumbone is the major component of the essential oil of wild ginger, Zingiber zerumbet Smith. It is not only highly reactive but also has diverse bioactivities. Those effects derive from two conjugated double bonds of zerumbone and a carbonyl group in between, and we had already established a synthetic scheme for zerumbone-pendant derivatives without disturbing the conjugation system. Herein, twelve conjugates with salicylic acid or various benzoic acid derivatives were synthesized for evaluations of their antiproliferative effects on Jurkat cells as salicylic acid is bioactive and has a carboxylic group for coupling. Most of them resulted in IC50 values as low as 1–10 μM, validating the utility of this activity-conserving strategy.Graphical abstractImage 1
       
  • Synthesis and enantioselective transport studies of both enantiomers of
           new chiral proton-ionizable crown ethers containing a diarylphosphinic
           acid unit
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Hajnalka Szabó-Szentjóbi, Péter Bagi, Judit Müller, György Tibor Balogh, Tünde Tóth, Péter Huszthy The synthesis of four new enantiopure crown ethers containing a diarylphosphinic acid unit has been carried out. As a continuation of our work in this field, the enantioselective transport ability of these ligands for chiral amines has been studied in an aqueous source phase/lipophilic organic bulk liquid membrane/aqueous receiving phase system controlled by the pH of the media. By altering the structures of the carriers we improved the enantioselectivity of the transport.Graphical abstractImage 1
       
  • Expected and unforeseen reactions of
           2,3,3-trimethyl-1λ6-isothiazolidine-1,1,4-trione and their spiro
           derivative
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Maria V. Popova, Alexey V. Dobrydnev, Viktoriya V. Dyakonenko, Irina S. Konovalova, Svitlana V. Shishkina, Yulian M. Volovenko Herein, we present a full account of our studies with respect to the reactivity of insufficiently explored 1λ6-isothiazolidine-1,1,4-triones (so-called β-keto-γ-sultams). This heterocyclic system possesses two reaction centers: the EWG-activated methylene group and the carbonyl moiety which were investigated in the course of present study. 2,3,3-Trimethyl-1λ6-isothiazolidine-1,1,4-trione and 4-methyl-5λ6-thia-4-azaspiro[2.4]heptane-5,5,7-trione were chosen as representatives of the given class of substances. The former is a classical spatially uncomplicated model substance, the latter bearing a spiranic cyclopropane substituent is interesting in terms of evaluation of strain cycle effects. Indeed, the data obtained convey information about the impact of the highly strained substituent on the reaction centers of the ketosultam core. Thus, in addition to less stability of the strained spiranic ketosultam, the reactivity of its carbonyl group is suppressed whereas the activity of the methylene group is enhanced being compared with the nonspiranic substrate. Apart from the difference in the chemical character of the given β-keto-γ-sultams we faced unprecedented products (1,1-dioxo-5-[2-(triphenylphosphonio)acetyl]-2,3-dihydro-1H-1λ6-isothiazol-4-olates) formed during the course of the reaction with the Wittig reagent triphenylcarbethoxymethylenephosphorane.Graphical abstractImage 1
       
  • Mn(III)-promoted synthesis of spiroannular tricyclic scaffolds via
           sulfonylation/dearomatization of biaryl ynones
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Li Zhou, Yu Xia, Yu-Zhao Wang, Jun-Dan Fang, Xue-Yuan Liu A Mn(III)-promoted radical oxidative ipso-annulation reaction of biaryl ynones with sodium sulfinates to construct various substituted spiro[5.5]trienones has been explored in this study. This protocol is characterized by mild reaction conditions, good substrates functional group compatibility, cheap and easily prepared Mn(OAc)3·2H2O, and it demonstrates a simple operation.Graphical abstractImage 1
       
  • A highly sensitive and selective fluorescent probe for Fe3+ containing two
           rhodamine B and thiocarbonyl moieties and its application to live cell
           imaging
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Zhigang Gao, Chun Kan, Haibo Liu, Jing Zhu, Xiaofeng Bao A novel turn-on rhodamine B-based fluorescent chemosensor (RBCS) was designed and synthesized by reacting N-(rhodamine B)lactam-1,2-ethylenediamine and carbon disulfide. Upon addition of Fe3+ in EtOH/H2O solution (2:1, v/v, HEPES buffer, 0.6 mM, pH 7.20), the RBCS displayed a significant fluorescence enhancement at 582 nm and a dramatic color change from colorless to pink, which can be detected by the naked eye. Significantly, the RBCS exhibited a highly selective and sensitive ability toward Fe3+. The detection limit of the probe was 2.05 × 10−7 M. Job's plot indicated the formation of 1:1 complex between the RBCS and Fe3+. Moreover, the practical use of the RBCS is demonstrated by its application in the detection of Fe3+ in HeLa cells.Graphical abstractUpon addition of Fe3+ in EtOH/H2O solution (2:1, v/v, HEPES buffer, 0.6 mM, pH 7.20), RBCS displayed a significant fluorescence enhancement at 582 nm and a dramatic color change from colorless to pink, which can be detected by the naked eye The detection limit of RBCS was 2.05 × 10−7 M. Job's plot indicated the formation of 1:1 complex between RBCS and Fe3+. Moreover, the practical use of RBCS is demonstrated by its application in the detection of Fe3+ in HeLa cells.Image 1
       
  • Synthetic studies towards the penicisulfuranols: Synthesis of an advanced
           spirocyclic diketopiperazine intermediate
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Kevin M. Gayler, Kyle M. Lambert, John L. Wood The 2,5-diketopiperazine (DKP) moiety is a core feature of many natural products and medicinally relevant scaffolds. As part of our efforts directed towards a total synthesis of penicisulfuranol B, we have developed and report herein: (1) the preparation of an N-hydroxy diketopiperazine intermediate accessible via a molybdenum-mediated oxidation of a parent diketopiperazine, and (2) further synthetic studies leading to a novel spirocyclic dihydrobenzofuran-containing diketopiperazine.Graphical abstractImage 1
       
  • Controlling the fluoridophilicity of sulfonium boranes via chelation,
           coulombic and hydrophobic effects
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Haiyan Zhao, Youngmin Kim, Gyeongjin Park, Francois P. Gabbai We describe the synthesis and properties of a series of sulfonium boranes featuring a dimesitylboryl unit and a dimethylsulfonium or methylphenyl sulfonium moiety connected by an ortho- or para-phenylene linker. Acid-base and fluoride anion tritration experiments carried out in aqueous media indicate that the [o-(Mes2B)C6H4(SMePh)]+ is the most Lewis acidic derivative. Structural and computational analysis indicate that the favorable properties of this cationic borane derive from the proximity of sulfonium and boryl units which enhance the Coulombic stabilization of the ensuing zwitterions o-(Mes2XB)C6H4(SMePh) with X = OH or F. Another important factor is the overall hydrophobicity of the sulfonium borane which, we propose, promotes anion desolvation, a factor also favoring B-X bond formation. Finally, the crystal structure of o-(Mes2FB)C6H4(SMePh) shows that the zwitterion is further stabilized by formation of a BF→S chelate motif.Graphical abstractImage 1
       
  • Reactive nitrogen species: Nitrosonium ions in organic synthesis
    • Abstract: Publication date: Available online 21 January 2019Source: TetrahedronAuthor(s): Luis Bering, Andrey P. Antonchick Nitrosonium ions are versatile and mild oxidants, which were successfully employed in organic transformations. The applications cover different fields, such as the functionalization of carbon-carbon and carbon-heteroatom bonds, functionalization of unsaturated bonds and the oxidative coupling of arenes, catalyzed by nitrosonium ions. Due to the ability of nitrosonium ions to modify various types of bonds with different modes of action, a variety of applications has been established, which addresses current challenges in organic chemistry research. By considering additional points, such as safety of reagents, by-product formation, employed solvents and energy consumption, several aspects of green and sustainable chemistry can be addressed. Within this review, synthetic applications of nitrosonium ions under transition metal-free reaction conditions are summarized.Graphical abstractImage 1
       
  • Preparing β-blocker (R)-Nifenalol based on enantioconvergent synthesis of
           (R)-p-nitrophenylglycols in continuous packed bed reactor with epoxide
           hydrolase
    • Abstract: Publication date: Available online 19 January 2019Source: TetrahedronAuthor(s): Fu-Long Li, Yu-Cong Zheng, Hao Li, Fei-Fei Chen, Hui-Lei Yu, Jian-He Xu An engineered epoxide hydrolase from Vigna radiate (VrEH2M263N) shows near-perfect enantioconvergence in single enzyme mediated hydrolysis of racemic p-nitrostyrene oxide (pNSO). To explore industrial potential of the promising biocatalyst, we tried to immobilize the VrEH2 variant by covalently linking onto a commercially available amino resin ECR8405F. Then a 5-mL packed bed reactor filled with the immobilized VrEH2M263N was connected with macroporous resin NKA-11 for in situ product adsorption, and the product (R)-p-nitrophenyl glycol (pNPG) was harvested by methanol elution, with 91% isolated yield and 97% ee. The continuous reactor was operated stably for more than 100 h with a space time yield of 20 g L−1 h−1. Subsequently, the β-blocker (R)-Nifenalol was prepared by chemically synthesized from (R)-pNPG, affording the product in an overall yield of 61.3% (1.5 g) and an enantiopurity of 99.9% ee after recrystallization.Graphical abstractImage 1
       
  • Stereoselective synthesis of cis-2,6-disubstituted piperidines
           from 1,2-cyclic sulfamidates
    • Abstract: Publication date: Available online 19 January 2019Source: TetrahedronAuthor(s): Mustafa Eskici, Abdullah Karanfil Diastereoselective synthesis of cis-2,6-disubstituted piperidines from 1,2-cyclic sulfamidates is described. Regioselective ring-opening reactions of 1,2-cyclic sulfamidates derived from L-phenylalanine, alanine, valine, norvaline with the ketal protected acetylide with a phenyl substituent proceed smoothly to form the N-sulfamate intermediates which on acidic hydrolysis give alkynylated amines with the ketal group intact. Hydrogenation of the alkynylated amines, debenzylation, ketal deprotection, subsequent cyclization (of aminoketones) and stereoselective hydrogenation of the cyclic iminium ion intermediates afford the corresponding cis-2,6-disubstituted piperidines in high diastereoselectivity (98% ≥ d.e.) with good chemical yields (68–86%). The present approach provides a novel route for the stereoselective synthesis of cis-2,6-disubstituted piperidines.Graphical abstractImage 1
       
  • One-pot, solvent-free Pd(II)-catalyzed direct β-C-H arylation of
           carboxamides involving anhydrides as substrates via in situ installation
           of directing group
    • Abstract: Publication date: Available online 18 January 2019Source: TetrahedronAuthor(s): Arup Dalal, Prabhakar Singh, Srinivasarao Arulananda Babu A one-pot, multicomponent-type, solvent-free Pd(II)-catalyzed direct β-C-H activation/arylation of carboxamides involving anhydrides as substrates via in situ installation of directing group (DG) is reported. Typically, the DG-assisted β-C-H activation/arylation of carboxamides is a two-step process comprising the installation of DG and Pd(II)-catalyzed C-H arylation. We attempted a multicomponent-type reaction comprising an anhydride, a DG (e.g. 8-aminoquinoline), an aryl iodide in the presence of the Pd(II) catalyst and an appropriate additive. Different anhydrides, DGs, aryl iodides, catalysts and additives were screened to reveal the scope of this multicomponent-type C-H arylation reaction process and various β-C-H arylated carboxamides were obtained in satisfactory to good yields.Graphical abstractImage 1
       
  • Stereoselective N-glycosylation with N 4-acyl cytosines and efficient
           synthesis of gemcitabine
    • Abstract: Publication date: Available online 17 January 2019Source: TetrahedronAuthor(s): Tongchao Liu, Jiadeng Tang, Jianpeng Liang, Yabin Chen, Xiaowen Wang, Jingkang Shen, Dongmei Zhao, Bing Xiong, Jun-Da Cen, Yue-Lei Chen Through systematical comparison of various N4-protected cytosine derivatives in the glycosylation step of gemcitabine synthesis, highly beta-stereoselective and high yielding TBAI catalyzed N-glycosylation was achieved with N4-Bz cytosine and anomeric mixture of 2,2‘-difluororibose mesylate donor. The subsequent global deprotection gave gemcitabine efficiently. Meanwhile, the anomeric chloride intermediate and fluoride-displaced side products of this N-glycosylation were identified, too. This new glycosylation method reveals the importance of N4-protection in the stereoselective preparation of pyrimidine nucleoside, also provides a potential alternative to current industrial process to gemcitabine.Graphical abstractImage 1
       
  • Isolation, structure elucidation, and antibacterial evaluation of the
           metabolites produced by the marine-sourced Streptomyces sp. ZZ820
    • Abstract: Publication date: Available online 14 January 2019Source: TetrahedronAuthor(s): Wenwen Yi, Qiao Li, Tengfei Song, Lei Chen, Xing-Cong Li, Zhizhen Zhang, Xiao-Yuan Lian New indole alkaloids streptoprenylindoles A–C (1–3) and diterpenoids 18-acetyl-cyclooctatin (8), 5,18-dedihydroxy-cyclooctatin (9), and 5-dehydroxy-cyclooctatin (10) were isolated from the culture of marine-derived Streptomyces sp. ZZ820, along with known 3-cyanomethyl-6-[3-methyl-2-butenyl]indole (4), N-(2-(1H-indol-3-yl)ethylacetamide (5), 1-acetyl-β-carboline (6), indole-3-methylethanoate (7), cyclooctatin (11), and chromomycin A3 (12). Their structures were elucidated by a combination of extensive spectroscopic analyses, ECD calculation, and the Mosher's method. Streptoprenylindoles A (1) and B (2) are enantiomers that were separated through the preparation of their Mosher esters. Three new diterpenoids (8–10) showed antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli with MIC values of 24.11–55.12 μM, while chromomycin A3 (12) showed potent antibacterial activities against MRSA (MIC: 0.59 μM) and E. coli (MIC 0.04 μM).Graphical abstractImage 1
       
  • Cu-catalyzed regio- and stereoselective sulfonylation of multi-substituted
           allenes
    • Abstract: Publication date: Available online 14 January 2019Source: TetrahedronAuthor(s): Shigeru Arai, Koki Matsumoto, Atsushi Nishida Regio- and stereoselective sulfonylation of allenes under Cu catalysis is described. Allenyl sp carbons exclusively react with TsCN to give the corresponding alkenyl sulfones. The reaction is initiated by addition of tosyl radical to form benzyl radical intermediates, which determines the reaction pathway. The structure of the products is highly dependent on the substituents on allenes.Graphical abstractImage 1
       
  • Design and synthesis of further simplified pyripyropene A based ACAT2
           selective inhibitors
    • Abstract: Publication date: Available online 14 January 2019Source: TetrahedronAuthor(s): Yi Liu, Xiaowei Zhang, Yang Zhan, Boliang Li, Wei Lu, Fajun Nan Acyl-coenzyme A: cholesterol acyltransferases (ACATs) play the significant role in the formation of cholesterol esters. One form of this enzyme is ACAT2, which not only regulates the balance of cholesterol metabolism in cells but also participates in the “escape” mechanism of hepatocellular carcinoma (HCC) cells. The natural product pyripyropene A (PPPA) and its analogs are the only chemical ACAT2-specific inhibitors. To develop simpler analogs and endeavor to remove a portion of multichiral centers and enrich a variety of analogs, new PPPA analogs are creatively designed and synthesized based on previous work. Among these new analogs, 7a and 9f show better activity and selective inhibition of ACAT2 compared with PPPA. These results will provide a new future for potential therapeutic use in atherosclerosis and HCC.Graphical abstractImage 1
       
  • Functionalized pyrroles from vinylaziridines and alkynes via
           rhodium-catalyzed domino ring-opening cyclization followed by C=C bond
           migration
    • Abstract: Publication date: Available online 14 January 2019Source: TetrahedronAuthor(s): Shu-Hao Wan, Shiuh-Tzung Liu Rhodium(I)-catalyzed intermolecular cycloadditions of alkynes with vinyl aziridines bearing a conjugated carbonyl group in the olefin moiety followed by the double migration resulted in the formation of pyrrole derivatives in a one pot fashion.Graphical abstractImage 1
       
  • Cinchona alkaloid derived squaramide catalyzed diastereo- and
           
    • Abstract: Publication date: Available online 12 January 2019Source: TetrahedronAuthor(s): Mei-Xin Zhao, Guang-Yu Zhu, Xiao-Li Zhao, Min Shi An efficient organocatalytic diastereo- and enantioselective Michael addition of α-substituted isocyanoacetates to 2-enoylpyridines catalyzed by cinchona alkaloid-derived squaramide has been achieved, affording the corresponding adducts with two adjacent tertiary-quaternary stereocenters in excellent yields (up to 99%) and good to excellent stereoselectivities (up to>20:1 dr, up to 98% ee) under mild conditions.Graphical abstractImage 1
       
  • PPh3/I2/HCOOH: An efficient CO source for the
           synthesis of phthalimides
    • Abstract: Publication date: Available online 12 January 2019Source: TetrahedronAuthor(s): Yingying Wang, Yang Zhou, Min Lei, Jinjun Hou, Qinghao Jin, Dean Guo, Wanying Wu A straightforward and general method has been developed for the synthesis of phthalimide derivatives from 2-iodobenzamides and PPh3/I2/HCOOH in the presence of a catalytic amount of Pd(OAc)2. The reaction results demonstrate that PPh3/I2/HCOOH is a facile, efficient and safe CO source. The whole process is carried out in toluene at 80 °C and furnishes the desired products in good to excellent yields.Graphical abstractImage 1
       
  • Flavin-dependent biocatalysts in synthesis
    • Abstract: Publication date: Available online 12 January 2019Source: TetrahedronAuthor(s): Summer A. Baker Dockrey, Alison R.H. Narayan The diverse chemistry possible with flavin cofactors positions flavin-dependent enzymes as versatile synthetic tools. This focused review highlights applications of flavin-dependent enzymes in organic synthesis. Select examples of monoamine oxidases, ene-reductases, monooxygenases and halogenases in target-oriented synthesis are presented.Graphical abstractImage 1
       
  • Sodium persulfate-promoted site-selective synthesis of mononitroarylamines
           under transition-metal-free conditions
    • Abstract: Publication date: Available online 11 January 2019Source: TetrahedronAuthor(s): De-Xun Xie, Hui-Juan Yu, Hui Liu, Wei-Cai Xue, Yuan-Shou Qin, Guang Shao A practical preparation of nitroarylamines from protected arylamines was herein disclosed. In this system, sodium nitrite acted as a nitration reagent in the presence of sodium persulfate without any transition-metal catalysts. This efficient site-selective protocol took place at room temperature for a short time through a free radical pathway.Graphical abstractA site-selective preparation of nitroarylamines was herein disclosed from protected arylamines and sodium nitrite in the presence of Na2S2O8 without any transition-metal-catalysts. The mild protocol took place at room temperature for a short time through a free radical mechanism with broad substrate scope and high efficiency.Image 1
       
  • Guianofruits C–I from fruit oil of andiroba (Carapa guianensis,
           Meliaceae)
    • Abstract: Publication date: Available online 11 January 2019Source: TetrahedronAuthor(s): Yuuta Tsukamoto, Hiroto Oya, Takashi Kikuchi, Takeshi Yamada, Reiko Tanaka Two novel chukrasone-type limonoids, named Guianofruits C and D (1 and 2), a guianolide derivative named Guianofruit E (3), and four novel phragmalin–type limonoids named Guianofruits F–I (4–7), were isolated from the fruit oil of Carapa guianensis AUBLET (Meliaceae), a traditional medicine in Brazil and Latin American countries. Their structures were mainly elucidated based on spectroscopic analyses using 1D and 2D NMR techniques. The effects of compounds 1–6 on the production of NO by LPS-activated mouse peritoneal macrophages were investigated. Two new chukrasone-type limonoids, Guianofruits C (1) and D (2), exhibited moderate inhibitory activities.Graphical abstractImage 1
       
  • Enantioselective Mannich reaction of γ-malonate-substituted
           α,β-unsaturated esters with N-Boc imines catalyzed by chiral
           bifunctional thiourea-phosphonium salts
    • Abstract: Publication date: Available online 30 December 2018Source: TetrahedronAuthor(s): Jiaxing Zhang, Gang Zhao A novel enantioselective Mannich reaction of γ-malonate-substituted α, β-unsaturated esters with N-protected arylaldimines was realized by using asymmetric phase-transfer catalysis (APTC). With amino acid-derived bifunctional thiourea-phosphonium salts as a catalyst, a series of enantio-enriched Mannich products could be synthesized under very mild and simple reaction conditions with high yields and enantioselectivities.Graphical abstractImage 1
       
  • Syntheses and biological evaluation of BE-43547A2 analogues modified at
           O35 ester and C15-OH sites
    • Abstract: Publication date: Available online 30 December 2018Source: TetrahedronAuthor(s): Yuanjun Sun, Ruifei Zhou, Honglei Xu, Dehong Wang, Xiuwen Su, Chao Wang, Yahui Ding, Liang Wang, Yue Chen Total syntheses of 6 BE-43547A2 analogues modified at O35 and C15 sites are reported. Late stage oxidation of 15-deoxy-BE-43547A2 delivered 15-epi-BE-43547A2, which verified the proposition that the C15 is an active site for late stage oxidation. The N35 and C15-F of analogues 1b and 1d were synthesized. Cellular level tests indicated O35 is a prohibitive site for modification and substitution of the OH at C15 with F or trim of the OH both led to a dramatic loss of activity. Compound 1e showed comparable inhibitory level towards Panc-1 cells, which indicated that the OH at C15 are permissive site for further modifications.Graphical abstractImage 1
       
  • Synthesis of the C6–C18 bis-tetrahydrofuran fragment of the proposed
           structure of iriomoteolide-2a via stepwise double SN2 cyclization
           reactions
    • Abstract: Publication date: Available online 26 December 2018Source: TetrahedronAuthor(s): Wen Zhang, Haichen Ma, Chuang-Chuang Li, Wei-Min Dai The C6–C18 bis-tetrahydrofuran (bis-THF) fragment of the proposed structure of iriomoteolide-2a has been synthesized via stepwise double intramolecular SN2-type etherifications. The C11 and C16 stereogenic centers could be secured in the forms of propargyl alcohols by asymmetric transfer hydrogenation of the corresponding propargyl ketones. The C9–C12 THF ring was first constructed via a tandem asymmetric dihydroxylation (AD)–SN2 sequence while the C13–C16 THF ring was later installed via an intramolecular SN2 reaction of a chiral propargyl mesylate. During the latter THF ring formation, epimerization at the propargylic carbon was not observed. Since the initially proposed (9R,11S,12R) configuration of iriomoteolide-2a has recently been revised to (9S,11R,12S), the established synthesis of the C6–C18 bis-THF fragment could be easily amended by using the opposite enantiomers of the chiral ligands for AD and asymmetric transfer hydrogenation.Graphical abstractImage 1
       
  • The journey of total synthesis toward nannocystin Ax
    • Abstract: Publication date: Available online 20 December 2018Source: TetrahedronAuthor(s): Rong Liu, Mengwei Xia, Yanhui Zhang, Shaomin Fu, Bo Liu Herein we describe present the detail on our full investigations that led to the achievement of the total synthesis of nannocystin Ax, a 21-membered macrocyclic natural product composing of a tripeptide fragment and a polyketide fragment, which featured in 8 longest linear steps in with 13.9% total overall yield. The key synthetic strategy relied on the late-stage stille coupling for the macrolactonization to construct the 21-membered ring, while direct connection between the tripeptide fragment and the polyketide fragment failed. 1H NMR experiments reveal that nannocystin Ax should exist as conformational mixtures in deuterated solvents.Graphical abstractImage 1
       
  • Ir-catalyzed chemoselective reduction of β-amido esters: A versatile
           approach to β-enamino esters
    • Abstract: Publication date: Available online 20 December 2018Source: TetrahedronAuthor(s): Zhi-Ping Yang, Guang-Sheng Lu, Jian-Liang Ye, Pei-Qiang Huang The conversion of β-amido esters to β-enamino esters is an indispensable step for some synthetic approaches to alkaloids and related medicines. Known methods for such transformation are not only stepwise, but also proceed with low atom-efficiency. Herein, we report a direct and versatile approach that features the Ir-catalyzed chemoselective reduction of β-amido esters with 1,1,3,3-tetramethyldisiloxane (TMDS). In addition, a lack of some signals was observed in the 13C NMR spectra of some alicyclic β-enamino esters. This revealed a longstanding existing but being ignored phenomenon in the literature.Graphical abstractImage 1
       
 
 
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