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Tetrahedron
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  • Collective total synthesis of botryanes
    • Abstract: Publication date: Available online 17 November 2018Source: TetrahedronAuthor(s): Chuang Qiao, Wen Zhang, Jing-Chun Han, Wei-min Dai, Chuang-Chuang Li The collective total synthesis of a series of botryanes, which are an important group of sesquiterpene antibiotics isolated from the metabolites of the fungus Botrytis cinerea, has been reported. The highly functionalized hydrindane skeleton of the botryanes was efficiently synthesized via an unusual intramolecular Diels-Alder reaction, which was promoted by TsOH as a protic acid. The concise total synthesis of (±)-hypocrolide A with a challenging hexacyclic skeleton was accomplished in 8 steps from the readily available starting materials.Graphical abstractImage 1
       
  • Total syntheses via cyclopropanols
    • Abstract: Publication date: Available online 16 November 2018Source: TetrahedronAuthor(s): Xinpei Cai, Weida Liang, Mingji Dai Cyclopropanols are readily available via the Kulinkovich cyclopropanation, the Simmons-Smith reaction, and other synthetic methods. Due to their intrinsic ring stains, cyclopropanols and their derivatives are highly reactive and can be converted to different structural scaffolds which are frequently found in many natural products. In this review, we highlight the applications of various cyclopropanol ring opening/expansion/fragmentation reactions in the total syntheses of natural products.Graphical abstractImage 1
       
  • Highly enantioselective 1,3-dipolar cycloaddition of imino esters with
           benzofuranone derivatives catalyzed by thiourea−quaternary ammonium salt
           
    • Abstract: Publication date: Available online 16 November 2018Source: TetrahedronAuthor(s): Ting Du, Zhaokun Li, Changwu Zheng, Guosheng Fang, Longhui Yu, Jun Liu, Gang Zhao Highly enantioselective 1, 3-dipolar cycloaddition of 2-arylidene-benzofuran- 3(2H)-ones with imino esters catalyzed by thiourea−quaternary ammonium salts has been developed. This reaction provides efficient construction of a range of chiral spiro[benzofuran-2,3′-pyrrolidine] in high yields (up to 99%) and with good enantioselectivities (up to 99% ee) under mild conditions.Graphical abstractImage 1
       
  • Synthesis of functionalized cage propellanes and D 3-Trishomocubanes via
           the ring-closing metathesis and acid-promoted rearrangement
    • Abstract: Publication date: Available online 16 November 2018Source: TetrahedronAuthor(s): Sambasivarao Kotha, Subba Rao Cheekatla Several functionalized cage propellanes and D3-trishomocubanes containing spiro linkage have been reported starting with commercially available materials such as 1,4-hydroquinone and dicyclopentadiene. In this regard, Claisen rearrangement, Diels–Alder reaction (DA), ring-closing metathesis (RCM) and acid-promoted rearrangement have been used as key steps. The strategies described here, opens up new opportunities to assemble intricate cage systems that are difficult to construct by conventional methods. Carbocation intermediates generated during the rearrangement process play a prominent role in designing unusual cage systems. One of the rearranged cage compound's structure was unambiguously established by single crystal X-ray diffraction studies.Graphical abstractImage 1
       
  • Organocatalytic double arylation of 3-isothiocyanato oxindoles:
           Stereocontrolled synthesis of complex spirooxindoles
    • Abstract: Publication date: Available online 16 November 2018Source: TetrahedronAuthor(s): Lin-Lin Zhang, Bing-Chao Da, Shao-Hua Xiang, Shuai Zhu, Zi-Yun Yuan, Zhen Guo, Bin Tan Quinones, precursors of aromatic structures, were firstly employed as the electrophiles for the organocatalytic Michael addition/cyclization cascade reaction with versatile 3-isothiocyanato oxindoles. Chiral bifunctional organocatalyst was appropriate for this enantioselective transformation to afford a variety of novel spirooxindoles, possessing a spirocyclic stereocenter adjacent to the aromatic ring, via asymmetric double arylation. These synthesized spirooxindoles are very difficult to access by the reported methods and were obtained in excellent chemical yields with excellent enantioselectivities.Graphical abstractImage 1
       
  • Chalcogen–chalcogen-bond activation by an ambiphilic, doubly reduced
           organoborane
    • Abstract: Publication date: Available online 15 November 2018Source: TetrahedronAuthor(s): Esther von Grotthuss, Felix Nawa, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner The 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene dianion salt Li2[1] instantaneously reacts with the dichalcogens O2(tBu)2, S2Me2, S2(pTol)2, Se2Ph2, and Te2Ph2 under reductive cleavage of the chalcogen–chalcogen bonds to give lithium chalcogenides and neutral 1. In solution, the products are involved in rapid association/dissociation equilibria. In the crystalline state, 1 and Li[O(tBu)] form a diadduct, whereas Li[SMe] gives a B⋯B-bridged monoadduct. In the three remaining cases, the crystal lattices contain monoadducts of 1 with one tri- and one tetracoordinate boron atom.Graphical abstractImage 1
       
  • Synthesis and theoretical study of pyrrole formiate derivatives through
           ring contraction of 1,4-dihydropyridines
    • Abstract: Publication date: Available online 15 November 2018Source: TetrahedronAuthor(s): Qiangwen Fan, Runzhi Sun, Zhichang Zhao, Hong Yan Pyrrole formiate derivatives were synthesized through ring contraction of corresponding 3-carboxylate-1,4-dihydropyridines (3-CDHPs) mediated by 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO). 2-Carboxylate-3-aryl-1H-pyrroles (2) and 3-carboxylate-4-aryl-1H-pyrroles (3) were obtained under readily accessible reaction conditions. To gain deep insights into this transformation, DFT calculations were carried out to establish the plausible reaction mechanism. The result revealed that the processes, including release of hydrogen, coupling with TEMPO, ring-opening of DHP scaffold, cleavage of ON bond in TEMPO moiety, fabrication of pyrrole scaffold and dissociation of formyl were incorporated in the transformation, which was confirmed further by the characterization of a byproduct and the detection of key intermediates using the LC-MS method.Graphical abstractAn alternative method for synthesizing pyrrole derivatives from corresponding 1,4-dihydropyrines is reported and detailed mechanism study of such transformation is performed by DFT calculations.Image 1
       
  • β-Shielded Michael systems whose H–C(sp2) deprotonation and
           1,2-addition reactions compete for organolithiums
    • Abstract: Publication date: Available online 15 November 2018Source: TetrahedronAuthor(s): Rudolf Knorr, Barbara Schmidt, Johannes Freudenreich, Therese von Roman Steric shielding of an α,β-unsaturated nitrile R2C = CH–CN by tert-alkyl β-substituents (R) prevented 1,4-additions of organolithiums and showed a remarkably solvent-dependent selectivity of tert-butyllithium (tBuLi): 1,2-addition at CN and α-deprotonation occurred almost equally fast in THF, while CN addition was exclusive in Et2O. The resultant N-lithioimine was cleanly α-deprotonated (albeit with unusual slowness) in situ by an excess of tBuLi. The imine was hydrolyzed to produce an enone R2C = CH–C(R') = O with bulky substituents R and R', which admitted CO addition but did not undergo α-deprotonation by mesityllithium, n-butyllithium (nBuLi), and even the very strong base tBuLi. 2,4,6-Tri-tert-butylphenyllithium (“Mes*Li”) did not add or deprotonate the enone. With N-lithio-2,2,6,6-tetramethylpiperidine (LTMP) as the catalyst, however, Mes*Li achieved α-deprotonation simultaneously with the known Mes* radical rearrangement and a subsequent carbonyl addition. With KOH or KOtBu as a base in [D6]DMSO (but not in DOCH3), the enone accomplished a rapid α-H/α-D exchange reaction at rt.Graphical abstractImage 1
       
  • Copper-catalyzed intramolecular redox reaction: Asymmetric synthesis of
           chiral 2-(1H-pyrrol-1-yl)-mandelic acid esters
    • Abstract: Publication date: Available online 15 November 2018Source: TetrahedronAuthor(s): Hong-Jin Du, Chao Lin, Xiaoan Wen, Qing-Long Xu An efficient approach to chiral α-hydroxy acid esters by Lewis acid-mediated asymmetric [1,5]-hydride shift and isomerization of 2-(3-pyrroline-1-yl)arylketone acid ester has been achieved in up to 96% yield and 94% ee. This protocol would be applied in the synthesis of chiral α-hydroxy acid derivatives with simplicity and high enantioselectivity.Graphical abstractImage 1
       
  • Copper(I)-catalyzed benzylic C(sp3)–H geminal difunctionalization:
           Successive oxidative intramolecular amidation and hydroxylation
    • Abstract: Publication date: Available online 15 November 2018Source: TetrahedronAuthor(s): Zhiguo Zhang, Songnan Wang, Chunfang Hu, Nana Ma, Guisheng Zhang, Qingfeng Liu A selective copper(I)-catalyzed benzylic C(sp3)–H geminal difunctionalization reaction of a benzylic-type sp3 carbon was developed. This novel strategy allowed simultaneous introduction of amide and hydroxyl group in a highly selective and efficient way via successive oxidative intramolecular amidation and hydroxylation. This method was also applied to the synthesis of 3-hydroxy-2,3-dihydro-1H-pyrrolo[3,4-b]quinoxalinones from readily available 3-methyl-N-substituted quinoxaline-2-carboxamides in moderate to good yields. The five-membered cyclic hemiaminal moiety of the pyrrolo[3,4-b]quinoxalinones can serve as an intermediates for subsequent transformations into other useful functional groups.Graphical abstractImage 1
       
  • P-stereogenic wide bite angle diphosphine ligands
    • Abstract: Publication date: Available online 14 November 2018Source: TetrahedronAuthor(s): Christine F. Czauderna, Alexandra M.Z. Slawin, David B. Cordes, Jarl Ivar van der Vlugt, Paul C.J. Kamer Two modular synthetic approaches for the preparation of novel wide bite angle diphosphine ligands containing stereogenic P-atoms have been developed, leading to compounds (S,S)-2,2′-bis(methylphenylphosphino)diphenyl ether (L1) and (S,S)-2,2′-bis(ferrocenylphenylphosphino)diphenyl ether (L2) in very good diastereomeric ratios. Both protocols involve diphenyl ether as backbone and (2RP,4SC,5RC)-(+)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine borane (RP)-5 as initial auxiliary to induce chirality at phosphorus. The absolute configuration of intermediates (S,S)-9-(BH3)2 and (R,R)-10-(BH3)2 as well as the ligands (S,S)-L1-BH3 and (S,S)-L2 was determined by X-ray crystallographic analysis.Graphical abstractImage 1
       
  • An efficient Fe(III)-catalyzed 1,6-conjugate addition of para-quinone
           methides with fluorinated silyl enol ethers toward β,β-diaryl
           α-fluorinated ketones
    • Abstract: Publication date: Available online 14 November 2018Source: TetrahedronAuthor(s): Yong-Jia Hao, Xiao-Si Hu, Jin-Sheng Yu, Feng Zhou, Ying Zhou, Jian Zhou Reported here is a highly efficient 1,6-conjugate addition of fluorinated silyl enol ethers to para-quinone methides, allowing facile access to a range of β,β-diaryl α-fluorinated ketones with good to high yields. Fe(OTf)3 was identified as the optimal catalyst, with the loading of 3 mol%. Notably, this represent the first 1,6-conjugate addition with fluorinated silyl enol ethers. The synthetic potential of the resulting adducts is also demonstrated.Graphical abstractImage 1
       
  • Graphical abstract TOC
    • Abstract: Publication date: 13 December 2018Source: Tetrahedron, Volume 74, Issue 50Author(s):
       
  • Graphical abstract TOC cont'd
    • Abstract: Publication date: 13 December 2018Source: Tetrahedron, Volume 74, Issue 50Author(s):
       
  • Graphical abstract TOC
    • Abstract: Publication date: 13 December 2018Source: Tetrahedron, Volume 74, Issue 50Author(s):
       
  • Formal synthesis of actinoranone using a one-pot semipinacol
           rearrangement/wittig reaction
    • Abstract: Publication date: Available online 14 November 2018Source: TetrahedronAuthor(s): Martina Menger, Mathias Christmann Here, we report a formal synthesis of the marine cytotoxic meroterpenoid actinoranone. Key steps include a semipinacol rearrangement/Wittig reaction sequence and a chiral pool approach for the syntheses of the tetralone and the ocatalin fragments, respectively. The presented route provides access to the natural product in 14 steps in the longest linear sequence.Graphical abstractImage 1
       
  • Novel concurrent redox cascades of (R)- and (S)-carvones enables access to
           carvo-lactones with distinct regio- and enantioselectivity
    • Abstract: Publication date: Available online 13 November 2018Source: TetrahedronAuthor(s): Naseem Iqbal, Jon D. Stewart, Peter Macheroux, Florian Rudroff, Marko D. Mihovilovic Within this study, we investigated a one-pot enzymatic redox cascade composed of different enoate reductases (5 EREDs from diverse bacterial origins) and various Baeyer-Villiger monooxygenases (4 BVMOs) with complementary regioselectivity that enabled access to six out of eight carvo-lactone stereoisomers starting from readily available natural carvones. Applicability of this two-step cascade was demonstrated by preparative scale experiments yielding up to 76% of the desired chiral carvolactone.Graphical abstractImage 1
       
  • A synthesis of cephalostatin 1
    • Abstract: Publication date: Available online 13 November 2018Source: TetrahedronAuthor(s): Yong Shi, Qing Xiao, Quan Lan, Da-Hai Wang, Lan-Qi Jia, Xiao-Hu Tang, Tao Zhou, Min Li, Wei-Sheng Tian A synthesis of cephalostatin 1 from hecogenin is described in detail. The gram-scale synthesis of south part features a Baeyer–Villiger oxidation of hecogenin to 16,20-diol, a selective oxidation of C16OH with Dess–Martin periodinane, a Rh(I)-catalyzed C15C16 double bond shift to C14C15 position, and a Hg(OAc)2-mediated spiroketal formation from cyclic enol ethers with alkenyl side chain at 2-position. Key transformations in the synthesis of north part, also on gram scale, include an abnormal Baeyer–Villiger oxidation of hecogenin to the corresponding dinorcholanic lactone, where a catalytic amount of iodine acts as a traceless and catalytic switch, an umpolung of steroidal 22-aldehyde to forge C22C23 bond with good stereochemical control, a cascade spiroketal-forming process to establish DEF rings in one operation, and a selective oxidation of C3OH. There are also other noteworthy transformations that, although not used in our final route, are valuable and could be applied to other syntheses, including: intra- or intermolecular SN2′ processes of C14-heteroatom-substituted C15C16 alkenes, an unprecedented rearrangement of β-adduct of D-ring dienes and singlet oxygen, a chelation-controlled methylallylation of C23 aldehyde, and so on.Graphical abstractImage 1
       
  • Astolides A and B, antifungal and cytotoxic naphthoquinone-derived polyol
           macrolactones from Streptomyces hygroscopicus
    • Abstract: Publication date: Available online 13 November 2018Source: TetrahedronAuthor(s): Vera A. Alferova, Roman A. Novikov, Olga P. Bychkova, Eugene A. Rogozhin, Maxim V. Shuvalov, Igor A. Prokhorenko, Vera S. Sadykova, Alexander B. Kulko, Lyubov G. Dezhenkova, Elena A. Stepashkina, Mikhail A. Efremov, Olga N. Sineva, Gulnara Kh. Kudryakova, Aleksander S. Peregudov, Pavel N. Solyev, Yaroslav V. Tkachev, Galina B. Fedorova, Larisa P. Terekhova, Anton P. Tyurin, Aleksey S. Trenin Two new natural compounds, astolides A,B, were isolated from Streptomyces hygroscopicus collected from the alkaline soil obtained from Saratov region, Russia. The structures were elucidated by interpretation of UV spectroscopic, MS, 1D and 2D NMR data. The relative configurations were determined by analysis of NOESY/ROESY spectra and coupling constants. The isolated compounds were evaluated for their inhibitory activity against bacteria, fungi and yeasts and showed pronounced antifungal activity. Both compounds are noticeably cytotoxic, being active against doxorubicin-resistant human leukemia cell line.Graphical abstractTwo new natural products astolides A,B from Streptomyces hygroscopicus show pronounced antifungal and cytotoxic activity.Image 1
       
  • Nucleophilic 5-endo-trig cyclization of 2-(trifluoromethyl)allylic metal
           enolates and enamides: Synthesis of tetrahydrofurans and pyrrolidines
           bearing exo-difluoromethylene units
    • Abstract: Publication date: Available online 13 November 2018Source: TetrahedronAuthor(s): Takeshi Fujita, Masahiro Hattori, Masaaki Matsuda, Ryutaro Morioka, Tanner C. Jankins, Masahiro Ikeda, Junji Ichikawa Ketones and imines bearing a 2-(trifluoromethyl)allylic moiety successfully underwent nucleophilic 5-endo-trig cyclization via their metal enolates and enamides. O- or N-Cyclization proceeded exclusively in each case to afford the corresponding five-membered heterocycles with both exo-difluoromethylene and exo-alkylidene units. On treatment with potassium hexamethyldisilazide (KHMDS) or lithium diisopropylamide (LDA), 2-(trifluoromethyl)allylic ketones or imines provided the corresponding tetrahydrofurans or pyrrolidines bearing a Z-alkylidene group with perfect or substantial stereoselectivity, respectively.Graphical abstractImage 1
       
  • An improved synthesis of pennogenin
    • Abstract: Publication date: Available online 13 November 2018Source: TetrahedronAuthor(s): Ran Gao, Yong Shi, Wei-Sheng Tian An improved synthesis of pennogenin, a bioactive component of Chinese herb “Chonglou” (Paris), is described. A ring-switching process opened the ring E of diosgenin and allowed the use of a hydroxyl-directed diboration/oxidation to introduce C17α-OH, hence eliminating the use of OsO4. This strategy might be rendered to synthesize similar steroids with C17α-OH.Graphical abstractImage 1
       
  • Working with Sir Derek H. R. Barton. “Chemistry, through Chemistry
           and For Chemistry”
    • Abstract: Publication date: Available online 12 November 2018Source: TetrahedronAuthor(s): Jeffrey I. Seeman The author reports on his experience as editor of Derek H. R. Barton's autobiography, Some Recollections of Gap Jumping, and video documentary of Barton less than a year before his death on March 16, 1998.Graphical abstractImage 1
       
  • Higher-order cycloaddition reactions: A computational perspective
    • Abstract: Publication date: Available online 12 November 2018Source: TetrahedronAuthor(s): Teresa A. Palazzo, Karl Anker Jørgensen Higher-order cycloaddition reactions are more common in the chemical literature now than ever before. With this class of reactions, we see a prime example of experimental and computational science working together to drive innovation. Here, we present a brief overview of some of the computational developments with a focus on how this work has driven experiment and vice versa.Graphical abstractImage 1
       
  • Unusual formation of novel highly substituted
           N-(3-indolyl)-imidazoles
    • Abstract: Publication date: Available online 9 November 2018Source: TetrahedronAuthor(s): Ji Qu, Mohan Bhadbhade, Naresh Kumar, David StC. Black Treatment of 3-amidoindoles with phosphoryl chloride leads to a dimerization of the resulting iminochlorides to form tetrasubstituted imidazoles in moderate yield. One indole ring undergoes ring-opening to allow the formation of the imidazole ring. This strategically simple synthesis considerably expands the scope of delivering N-indolylimidazoles.Graphical abstractImage 1
       
  • From one to two quaternary centers: Ester or nitrile α-alkylation applied
           to bioactive alkaloids
    • Abstract: Publication date: Available online 8 November 2018Source: TetrahedronAuthor(s): Nicholas Voute, Andrew R. Neal, Federico Medda, Craig A. Johnston, Alexandra M.Z. Slawin, Nicholas J. Westwood The synthesis of all-carbon quaternary centers remains a challenge. Here we describe studies on the formation of two adjacent all-carbon quaternary centers in the context of the planned synthesis of the bioactive natural products perophoramidine and the communesins. In one approach the key step involves ester-alkylation using either allyl bromide or formaldehyde as the electrophile. An unexpected rapid auto-oxidation reaction during the synthesis of the alkylation substrates limited the scalability of this approach. In a second route, alkylation of a nitrile-containing precursor was planned. The use of the TosMIC reagent on a complex substrate gave the nitrile for alkylation. The assignment of the relative stereochemistry of the products was done through the extensive use of small molecule X-ray crystallography.Graphical abstractImage 1
       
  • Graphical abstract TOC
    • Abstract: Publication date: 6 December 2018Source: Tetrahedron, Volume 74, Issue 49Author(s):
       
  • Graphical abstract TOC cont'd
    • Abstract: Publication date: 6 December 2018Source: Tetrahedron, Volume 74, Issue 49Author(s):
       
  • Graphical abstract TOC
    • Abstract: Publication date: 6 December 2018Source: Tetrahedron, Volume 74, Issue 49Author(s):
       
  • A new fluorescence probe based on diarylethene with a benzothiazine unit
           for selective detection of Cd2+
    • Abstract: Publication date: Available online 8 November 2018Source: TetrahedronAuthor(s): Zhen Wang, Shiqiang Cui, Shouyu Qiu, Shouzhi Pu A novel photochromic diarylethene derivative containing a benzothiazine unit has been synthesized. Its photochromism and fluorescent selectivity to metal ions were studied in detail in methanol solution. Under the stimulation of Cd2+ ions, the derivative showed a significant fluorescence enhancement and obvious red shift, accompanied by the fluorescent color changed from dark purple to bright blue. The 1: 1 stoichiometry between the derivative and Cd2+ was verified by titration experiments and high resolution mass spectrometry. In addition, a molecular logic circuit was designed with the emission intensity at 476 nm as output and the stimuli of Cd2+/EDTA and UV/vis as inputs.Graphical abstractImage 1
       
  • Recyclable alkylated fac-Ir(ppy)3 complex as a visible-light photoredox
           catalyst for the synthesis of 3-trifluoromethylated and
           3-difluoroacetylated coumarins
    • Abstract: Publication date: Available online 7 November 2018Source: TetrahedronAuthor(s): Xiaodan Zhang, Yaming Li, Xinyu Hao, Kun Jin, Rong Zhang, Chunying Duan A recyclable fac-tris(heptadecanyl-2-phenylpyridine) iridium [fac-Ir(hdppy)3] photocatalyst was synthesized. The hexane-phase-selective solubility of fac-Ir(hdppy)3 in a thermomorphic multicomponent solvent (TMS) allowed its easy recycling by automatic liquid/liquid separation at room temperature. The excellent catalytic and recoverable activities of fac-Ir(hdppy)3 were demonstrated via trifuoromethylation and difluoroacetylation reactions of phenyl 3-phenylpropiolate under visible-light irradiation in a TMS system.Graphical abstractImage 1
       
  • Selective synthesis of oxazoles and pyrazines from
           α-bromo-1-phenylethanone using a by-product-promoted strategy
    • Abstract: Publication date: Available online 6 November 2018Source: TetrahedronAuthor(s): Changhui Liu, Jiateng Zhao, Yu Qiao, Wenbo Huang, Zhonghao Rao, Yanlong Gu Oxazoles and pyrazines are fundamental heterocycles that widely found in natural products or drugs. In this work, a selective strategy for oxazoles and pyrazines synthesis using α-bromo-1-phenylethanone and ammonium acetate as starting materials was reported. This methodology features mild reaction conditions, readily accessible starting materials and good chemoselectivity. Mechanistic study indicates that this reaction involves a by-product-promoted (BPP) process for the formation of oxazole, that is, the in-situ formed hydrogen bromide (HBr) during the reaction promotes the whole tandem process.Graphical abstractImage 1
       
  • Harnessing sun for catalyst and sensitizer free regio- and
           stereo-selective [2+2] cycloaddition
    • Abstract: Publication date: Available online 6 November 2018Source: TetrahedronAuthor(s): Kunal Kumar Jha, Sanjay Dutta, Saibal Sar, Subhabrata Sen, Parthapratim Munshi Presence of cyclobutane rings in bioactive natural products makes them a popular synthetic target. Most common strategy for synthesizing cyclobutanes is [2+2] cycloaddition, which is usually facilitated by using ultraviolet radiation and catalysts. Herein we report the design and synthesis of densely functionalized cyclobutanes by alleviating these drawbacks and using sunlight. Further, we identified the putative mechanism of the transformation based on kinetic, fluorescence and crystallographic studies and evaluated biological activities of the products against MCF7 cell lines. The rational design of the olefinic substrates was based on their UV–vis spectra. The generic aspect of the reaction was elucidated by the syntheses of diverse analogs of cyclobutanes. Further, crystal structures and UV–vis spectra of the olefinic partners assisted us in rationalizing the stereoselectivity of the heterodimers. We believe this energy-efficient mild approach will provide a substantial contribution to the existing repertoire of strategies to regio- and stereoselectively access cyclobutanes.Graphical abstractImage 1
       
  • Application of vinylogous carbamates and vinylogous aminonitriles to the
           regiospecific synthesis of uniquely functionalized pyrroles and quinolones
           
    • Abstract: Publication date: Available online 5 November 2018Source: TetrahedronAuthor(s): John T. Gupton, Evan Crawford, Matt Mahoney, Evan Clark, Will Curry, Annie Lane, Alex Shimozono, Veronica Moore-Stoll, Kristen Elofson, Wen Juekun, Micah Newton, Scott Yeudall, Elizabeth Jaekle, Rene Kanters, James A. Sikorski Pyrroles and quinolones represent core structures, which are routinely found in both natural and synthetic bioactive substances. Consequently, the development of efficient and regiospecific methods for the preparation of such heterocycles with unique functionality is of some importance. We describe herein the regiospecific synthesis of 1,2,3,4-tetrasubstituted pyrroles containing polar substituents and such products are prepared from vinylogous carbamates and vinylogous aminonitriles. We also describe the regiospecific synthesis of 3-aryl containing 1,3,6-trisubstituted quinolones from vinylogous carbamates. The use of an amine exchange reaction to prepare precursors for the pyrrole and quinolone forming cyclizations represents a key factor in the strategy.Graphical abstractImage 1
       
  • The 2-acetylthioethyl ester group: A versatile protective group for
           P-OH-groups
    • Abstract: Publication date: Available online 5 November 2018Source: TetrahedronAuthor(s): Jens C. Markwart, Frederik R. Wurm Phosphodiesters are bridging elements in nucleic acids. In nature and synthesis, their negative charge protects them from hydrolysis and controls their solubility profile. RNA is a promising material for gene technology but cellular uptake is low due to negative charges. Synthetic oligonucleotides were delivered into cells by a prodrug approach relying on the enzymatic release of the polyphosphodiester oligonucleotides. In synthetic chemistry, a protective group for the POH functionality is often necessary, e.g. due to solubility or chemical incompatibility. Several methods for POH protection were proposed, but often with low selectivity or harsh conditions. Here, we present the 2-acetylthioethyl group as a versatile protective group for low molecular weight or polymeric phosphodiesters, which can be cleaved under acidic conditions in water or by hydrazine in THF to release the POH-functionality, but olefins remain intact. This straightforward use allows designing various synthetic polyphosphodiesters, e.g. for flame-retardant or dispersants.Graphical abstractImage 1
       
  • Deconvolution of E/Z tetrahydroisoquinoline amide rotamers and conformers
           from a marine-derived Streptomyces strain
    • Abstract: Publication date: Available online 5 November 2018Source: TetrahedronAuthor(s): Vanessa M. Nepomuceno, Hiyoung Kim, Yuanqing Ding, Hongbing Liu, Mark Sadek, Daneel Ferreira, Sesselja Omarsdottir, Brian T. Murphy A collaborative program to discover new specialized metabolites from aquatic environments of Iceland led to the deconvolution of tetrahydroisoquinoline amide E/Z rotamers [(E/Z)-N-acetyl-MY336-a; 1] and conformers produced by a Streptomyces sp. All structures were elucidated by NMR and MS analysis, and interpretation of electronic circular dichroism (ECD) data. ECD and optical rotation (OR) simulations permitted the unequivocal assignment of the absolute configuration of compound 1 and provided an important example of delineating the spectroscopic contributions of equilibrating rotamers and boat/chair conformers of a common natural product scaffold.Graphical abstractImage 1
       
  • Recent Development of Catalytic Trifluoromethoxylation Reactions
    • Abstract: Publication date: Available online 13 September 2018Source: TetrahedronAuthor(s): Katarzyna N. Lee, Johnny W. Lee, Ming-Yu Ngai Trifluoromethoxy (OCF3) group exhibits unique properties, which render it a highly desirable structural motif in life and materials sciences. The numbers of newly synthesized trifluoromethyl ethers are booming as new synthetic methods are constantly being developed to access these valuable compounds. This Review summarizes recent catalytic approaches towards preparation of trifluoromethyl ethers. Alkene, allylic, benzylic, and aryl trifluoromethoxylation reactions are discussed herein.Graphical abstractImage 1
       
  • Colour switching with photochromic vinylidene-naphthofurans
    • Abstract: Publication date: Available online 2 November 2018Source: TetrahedronAuthor(s): Diogo Costa, Céu M. Sousa, Paulo J. Coelho A series of novel photochromic vinylidene-naphthofurans with extended conjugation, and a free hydroxyl function, were easily prepared using the Suzuki reaction. After silanization, these dyes were embedded in ormosil matrices affording solid and transparent materials that acquire different colourations (violet, green, bluish), reversibly, when exposed to the UV (Sun) light, for 2 min, at room temperature. The presence of an extra phenyl ring in some positions affects both the λmax of absorption of the photochromic compounds in the uncoloured closed and open coloured form. After removal of the light source the materials lose progressively their coloration returning to the initial uncoloured state in less than 15 min at room temperature.Graphical abstractImage 1
       
  • C23+fragment+of+biselyngbyolide+A+and+B+enabled+by+transition+metal+catalysis&rft.title=Tetrahedron&rft.issn=0040-4020&rft.date=&rft.volume=">Stereoselective synthesis of the C14C23 fragment of biselyngbyolide A and
           B enabled by transition metal catalysis
    • Abstract: Publication date: Available online 2 November 2018Source: TetrahedronAuthor(s): Rakesh G. Thorat, Bailey A. Brooks, Brandon Nichols, Andrew M. Harned Transition metal catalysis has enabled the highly stereoselective and protecting group-free synthesis of the C14C23 fragment of the apoptosis-inducing natural products biselyngbyolide A and B. A Pd-catalyzed Stille reaction between a vinyl stannane and a crotyl carbonate formed the skipped diene with complete control of the trisubstituted bond and excellent control over the branched/linear products. A Cu-catalyzed Stahl oxidation was used to form the requisite aldehyde needed for a Ag-catalyzed asymmetric allylation. The latter provided the final fragment with excellent stereochemical control.Graphical abstractImage 1
       
  • Enantiopure (P)- and
           (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5]helicenediols and their
           helicene analogues: Synthesis, amplified circularly polarized luminescence
           and catalytic activity in asymmetric hetero-Diels–Alder reactions
    • Abstract: Publication date: Available online 1 November 2018Source: TetrahedronAuthor(s): Lei Fang, Meng Li, Wei-Bin Lin, Chuan-Feng Chen Three pairs of enantiopure (P)- and (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5]helicenediols (ArOH-H[5]HOLs), and enantiomers (P)- and (M)-3,14-bis(o-hydroxyphenyl)benzo[5]helicene-diols (PhOH-[5]HOLs) were designed and synthesized. It was found that compared with ArOH-H[5]HOLs, PhOH-[5]HOLs not only showed obvious red-shifts in both absorption and emission spectra, but also exhibited more intense CPL with amplified glum, which might be attributed to the more rigid structure of PhOH-[5]HOLs. However, rigid PhOH-[5]HOLs was less effective in the catalytic asymmetric hetero-Diels–Alder (HAD) reactions than those of ArOH-H[5]HOLs with the flexible tetrahydro[5]helicene backbone that could adjust conformation to suit the substrates. Therefore, the helical chirality amplification and chirality transfer could be efficiently achieved by adjusting the rigid and flexible structures of helical molecules, which might provide a useful strategy to optimize the structure of helicence derivatives for their applications in chiroptical materials and asymmetric catalysis.Graphical abstractImage 1
       
  • Rhodium(III)-catalyzed C-H alkylation of heterocycles with allylic
           alcohols in water: A reusable catalytic system for the synthesis of
           β-aryl ketones
    • Abstract: Publication date: Available online 1 November 2018Source: TetrahedronAuthor(s): Xiang Li, Feng Zhang, Dan Wu, Yirui Liu, Gan Xu, Yanli Peng, Zixiong Liu, Yuxin Huang A highly efficient, green and sustainable protocol for rhodium(III)-catalyzed C-H alkylation of heterocycles with allylic alcohols has been achieved, which affords a series of β-aryl ketones in high yields. The reaction proceeds smoothly in water under air, and works well with heterocycles such as indoles, indolines, pyrroles and carbazoles. Notably, the expensive rhodium catalyst in water could be easily separated from the organic products, and reused for at least five times without loss of its catalytic activity and selectivity, which is a promising, green and sustainable pathway for the synthesis of β-aryl ketones. To the best of our knowledge, this is the first example for the reuse of expensive rhodium catalyst in water.Graphical abstractImage 1
       
  • Recent advances in the functionalization of allenes via radical process
    • Abstract: Publication date: Available online 31 October 2018Source: TetrahedronAuthor(s): Guanyinsheng Qiu, Jun Zhang, Kaida Zhou, Jie Wu This review is focused on the recent advances in the functionalization of allenes via radical process. Different radical partners including carbon radicals and heteroatom radicals are discussed in the reactions of allenes. Generally, the radical formed in situ would attack the allene at the central carbon leading to allyl radical intermediate. However, the formation of alkenyl radical intermediate from allene could be observed as well in some cases with high regioselectivity and stereoselectivity.Graphical abstractRecent advances in the functionalization of allenes via radical process are summarized. Different radical partners including carbon radicals and heteroatom radicals are discussed in the reactions of allenes.Image 1
       
  • Acid-mediated four-component tandem cyclization: Access to multifused
           1,3-benzoxazine frameworks
    • Abstract: Publication date: Available online 31 October 2018Source: TetrahedronAuthor(s): Jungang Wang, Rongrong Zhou, Shiyi Zhuang, Anxin Wu An acid-mediated multicomponent reaction has been developed for the direct synthesis of multifused 1,3-benzoxazine derivatives from simple and readily available arylglyoxal monohydrates and 2-aminobenzyl alcohols under mild conditions. This novel protocol is proposed to proceed through intramolecular poly-heterocyclizations, thus leading to the formation of three new rings and six new chemical bonds, including four C−N and two C−O bonds.Graphical abstractImage 1
       
  • Copper catalysed cross-dehydrogenative coupling (CDC) reaction of
           4-thiazolidinone with terminal alkyne
    • Abstract: Publication date: Available online 31 October 2018Source: TetrahedronAuthor(s): Mohammedumar M. Shaikh, Anuj P. Patel, Kishor H. Chikhalia Cross dehydrogenative coupling (CDC) strategy has been employed for C-alkynylation of 4-thiazolidinone with terminal alkyne under copper catalysis. Present reaction involves coupling of C(sp3) adjacent to sulfur of 4-thiazolidinone with C(sp) of terminal alkyne under CDC strategy is unprecedented to the best of our knowledge. Significant functional group tolerance, considerable yield and DFT study for mechanism make this synthetic task more interesting and compatible.Graphical abstractImage 1
       
  • Asymmetric synthesis of D-fagomine and its diastereoisomers
    • Abstract: Publication date: Available online 31 October 2018Source: TetrahedronAuthor(s): Stephen G. Davies, Ai M. Fletcher, Matthew S. Kennedy, Paul M. Roberts, James E. Thomson A divergent strategy for the asymmetric syntheses of D-fagomine and three of its diastereoisomers has been developed. The diastereoselective conjugate addition of an enantiopure lithium amide to an α,β-unsaturated ester was used as the key step to install the correct configuration required for the C(5)-stereogenic centre within the targets. In situ enolate oxidation generated the corresponding anti-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both D-fagomine and D-3-epi-fagomine. Subsequent epimerisation of this key anti-α-hydroxy-β-amino ester upon oxidation and diastereoselective reduction gave the corresponding syn-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both D-4-epi-fagomine and D-5-epi-fagomine. Elaboration of both α-hydroxy-β-amino esters upon reduction to the corresponding aldehydes followed by aldol reaction generated the requisite C(3)-stereogenic centres within the target compounds, then cyclisation and deprotection gave the enantiopure iminosugars in good overall yields, as single diastereoisomers (>99:1 dr).Graphical abstractImage 1
       
  • Hyperbranched polymers with aggregation-induced emission property for
           solution-processed white organic light-emitting diodes
    • Abstract: Publication date: Available online 30 October 2018Source: TetrahedronAuthor(s): Dongyu Wu, Tiaomei Zhang, Jing Sun, Yuling Wu, Xiaoqing Liao, Guojing Lu, Jingjing Yang, Hua Wang, Lu Li, Bingshe Xu In this work, a new series of hyperbranched polymers of PFTPE-Ir(piq)3-X(X = 1, 5, 10) were designed and synthesized, in which tris(1-phenylisoquinoline)iridium(Ш) (Ir(piq)3) acts as red emission core and PFTPE acts as branches. The photophysical study reveals that these hyperbranched polymers exhibit aggregation-induced emission (AIE) characteristic, inducing in much higher photoluminescent quantum yield (ΦY) in neat film than that in dilute tetrahydrofuran (THF) solution. The white-light OLEDs using PFTPE-Ir(piq)3-X as emission layer show rather weaker efficiency roll-off. Especially, the white-light OLED based on PFTPE-Ir(piq)3-5 as emission layer shows a maximum luminance of 4686 cd/m2, a maximum luminous efficiency of 2.43 cd/A, a maximum external quantum efficiency of 1.08% and the Commission Internationale de l’Eclairage coordinate of (0.26, 0.36).Graphical abstractA series of hyperbranched copolymers were designed and synthesized, achieving the aggregation-induced emission (AIE) and a Commission International de l'Eclairage coordinate of (0.33, 0.34). Image 1
       
  • A computational study on the stereoselective reduction of cyclic ketones
           by LiAl(OR)3H in THF
    • Abstract: Publication date: Available online 30 October 2018Source: TetrahedronAuthor(s): Gerald J. Tanoury, Stephanie Roeper As part of the development of the ketone reduction step for the drug substance manufacturing process of VX-222, the mechanism for stereoselective reduction of model compound 4-tert-butylcyclohexanone by LiAlH(OMe)3 with explicit THF mono- and bissolvation was studied computationally with three DFT functionals (B3LYP, B3LYP-D3 and M06-2X). The calculations provide a detailed and quantitative description of the stepwise mechanism for this polarized reaction: C-H bond formation followed by Al-O bond formation.Graphical abstractImage 1
       
  • Photoredox mediated annelation of iododifluoromethylated alcohols with
           1,1-diarylethylenes
    • Abstract: Publication date: Available online 29 October 2018Source: TetrahedronAuthor(s): Liubov I. Panferova, Grigory N. Chernov, Vitalij V. Levin, Vladimir A. Kokorekin, Alexander D. Dilman A method for the synthesis of 3,3-difluorotetrahydrofurans from iododifluoromethylated alcohols and 1,1-diarylethylenes is described. The reaction is performed under irradiation with 400 nm light emitting diodes in the presence of a cationic iridium(III) photocatalyst, [Ir(ppy)2(dtbbpy)]PF6, substoichiometric amounts of triphenylphosphine and sodium trifluoroacetate as a base.Graphical abstractImage 1
       
  • Three-step synthesis of chiral and sterically hindered amino alcohols
           based on cyclic enol phosphates
    • Abstract: Publication date: Available online 29 October 2018Source: TetrahedronAuthor(s): Krzysztof Owsianik, Ewa Krawczyk, Grażyna Mielniczak, Marek Koprowski, Lesław Sieroń The new synthesis of chiral and sterically hindered 1,2-amino alcohols derivatives of 2-methyl-indane and 1,2,3,4-tethrahydrophenanthrene based on cyclic enol phosphates were investigated. The desired products were obtained using three step procedure: oxidation of accessible enol phosphates, transformation α-hydroxy ketones into corresponding oximes and finally reduction of the last one to 1,2-amino alcohols. The optimal conditions of all stages to obtain products with high enantioselectivity or diastereomeric ratio were found and elaborated. The structures and absolute configurations of (3R)-2,3-dihydro-3-hydroxy-1H-phenanthren-4-one and corresponding oxime were confirmed by X-ray analysis.Graphical abstractImage 1
       
  • A metal-free, hypervalent iodine(III)-induced tandem oxidative
           cycloisomerization based process for preparation of fluorescent diethyl
           5,5′-diaryl-2,2′-bifuran-4,4′-dicarboxylates
    • Abstract: Publication date: Available online 29 October 2018Source: TetrahedronAuthor(s): Lin Mei-Huey, Yang Tsung-Jung A new method has been developed for concise synthesis of diethyl 5,5′-diaryl-2,2′-bifuran-4,4′-dicarboxylates. The preparative pathway begins with bis-C-alkylation reaction of the β-ketoester and 1,4-dibromobut-2-yne followed by hypervalent iodine (III)-mediated oxidative cycloisomerization reaction of the formed symmetric γ-alkynyl-diketones. The novel diethyl 5,5′-diaryl-2,2′-bifuran-4,4′-dicarboxylates, formed by using this process were found to possess unique fluorescence properties.Graphical abstractImage 1
       
  • Activation of dihydrogen by 1,4,2,5-diazadiborinine
    • Abstract: Publication date: Available online 29 October 2018Source: TetrahedronAuthor(s): Baolin Wang, Rei Kinjo Activation of dihydrogen (H2) by 1,4,2,5-diazadiborinine is reported. Under the heating condition, treatment of 1,4,2,5-diazadiborinine with H2 results in the cleavage of HH bond, to afford product 2, which was fully characterized by NMR and IR spectroscopy as well as X-ray diffraction and HRMS analysis. In the presence of borane dimethylsulfide complex (BH3·SMe2), 2 readily isomerizes to 3 under the mild reaction condition.Graphical abstractImage 1
       
  • Eremophilane-type sesquiterpenoids in a deep-sea fungus Eutypella sp.
           activated by chemical epigenetic manipulation
    • Abstract: Publication date: Available online 28 October 2018Source: TetrahedronAuthor(s): Siwen Niu, Dong Liu, Zongze Shao, Peter Proksch, Wenhan Lin Cultivation of a deep-sea-derived fungus Eutypella sp. MCCC 3A00281 by a chemical epigenetic manipulation using suberohydroxamic acid (SBHA), a histone deacetylase inhibitor (HDI), resulted in the significant change of the metabolite profile. Chromatographic application of the extended metabolites led to the isolation of a total of 30 eremophilane-type sesquiterpenoids, of which 26 were identified as new entities namely eutyperemophilanes A-Z (1–26). Their structures were established by extensive analyses of the 1D and 2D NMR, and HRESIMS data, as well as the modified Mosher's method, X-ray crystallography, and ECD data for the assignment of their absolute configurations. Most eremophilanes from the fungal strain showed a trans-fusion of rings A and B, uncommonly found from nature. All compounds were evaluated for the inhibitory effects toward the nitric oxide (NO) production that was induced by lipopolysaccharide (LPS) in RAW 264.7 macrophage cells, while compounds 9 and 10 exerted significant inhibition.Graphical abstractImage 1
       
  • Total synthesis of (−)-cleistenolide and formal synthesis of herbarumin
           I via a diastereoselective modulable allylation
    • Abstract: Publication date: Available online 28 October 2018Source: TetrahedronAuthor(s): Pol Karier, Gheorghe C. Catrinescu, Nicolas Diercxsens, Koen Robeyns, Michael Singleton, István E. Markó A modulable tin based allylation method for the synthesis of 1,2,3-triols is described. The optimization of the reaction was aided by 1H and 119Sn low temperature NMR spectroscopic investigations, which support the formation of two cyclic intermediates after transmetallation. Depending on the nature of the Lewis acid, either syn/anti or anti/syn configured triols could be obtained with good stereocontrol. To demonstrate the value of this methodology and the resulting scaffolds, they were used to install the signature triol motifs of (−)-cleistenolide and of herbarumin I.Graphical abstractImage 1
       
  • Cross-dehydrogenative coupling strategy for phosphonation and cyanation of
           secondary N-alkyl anilines by employing
           2,3-dichloro-5,6-dicyanobenzoquinone
    • Abstract: Publication date: Available online 27 October 2018Source: TetrahedronAuthor(s): Qing Liu, Shuchen Yu, Liangzhen Hu, Muhamad Ijaz Hussain, Xiaohui Zhang, Yan Xiong The cross-dehydrogenative coupling strategy for metal-free phosphonation and cyanation of secondary N-alkyl anilines has been developed firstly under mild reaction conditions. Based on detailed optimization of reaction conditions, the substrate generality of N-alkyl anilines and various hydrogen phosphonates has been investigated, and a series of versatile α-aminophosphonates and α-aminonitriles were therefore furnished in good to excellent yields. A plausible collective reaction mechanism through dehydrogenation to imine formation, then to respective α-aminophosphonates and α-aminonitriles was proposed.Graphical abstractImage 1
       
  • Cyclobutane-based peptides / terpyridine conjugates: Their use in metal
           catalysis and as functional organogelators
    • Abstract: Publication date: Available online 27 October 2018Source: TetrahedronAuthor(s): Oriol Porcar-Tost, Bernat Pi-Boleda, Jordi García-Anton, Ona Illa, Rosa M. Ortuño Two new conjugates, hcptpyDP and hcptpyTP, of a terpyridine derivative incorporating artificial peptide moieties, have been synthesized and their use in the preparation of metal catalysts and organogelators has been investigated. Ru(II) complexes derived from these ligands showed electrochemical behavior and activity as catalysts in the epoxidation of olefins similar to that of Beller's catalyst. As organogelators, these conjugates were able to gelate a variety of solvents, from toluene to methanol, with satisfactory mgc (minimum gelation concentration) values. The presence of 4′-(4-carboxy)phenylterpyridine (hcptpy) moiety allows tuning the gelling properties and also influences the supramolecular self-assembling mode to produce chiral aggregates with respect to parent peptides DP and TP. In the case of the conjugates, π−π interactions provided by the aromatic moieties cooperate with inter-molecular hydrogen bonding between NH and CO in the amide groups. Further properties of peptide/terpyridine conjugates are under investigation in view of future applications.Graphical abstractImage 1
       
  • One-pot synthesis of carbohydrate exo-cyclic enones and hemiketals with
           6,8-dioxabicyclo-[3.2.1]octane moieties. Serendipitous formation of a
           spironolactone when 2-pyridinecarboxaldehyde is used as the reactant. Part
           II
    • Abstract: Publication date: Available online 26 October 2018Source: TetrahedronAuthor(s): Rachael E. Hohol, Holly Arcure, Zbigniew J. Witczak, Roman Bielski, Kristin Kirschbaum, Peter Andreana, Donald E. Mencer A library of exo-cyclic carbohydrate enones 2–13 were prepared via a base-catalyzed, highly stereoselective aldol condensation of dihydrolevoglucosenone 1 (cyrene) with various aromatic aldehydes. In the case of 4-chlorobenzaldehyde as a reactant, under conditions of the aldol condensation, exo-cyclic enone 9 and a secondary product 9A was isolated. When 2-pyridinecarboxaldehyde was used as a reactant, an unexpected spironolactone 19 was exclusively observed. 1H NMR, 13C NMR, MS analyses and single-crystal x-ray diffraction of the representative enone 9, the secondary product 9A, hemiketal 18, and spironolactone 19 unequivocally confirms the structural assignments. Mechanistic insights leading to the synthesized products are also proposed and discussed.Graphical abstractImage 1
       
  • Oxidative cross-coupling of allyl(trimethyl)silanes with aryl boronic
           acids by palladium catalysis
    • Abstract: Publication date: Available online 26 October 2018Source: TetrahedronAuthor(s): Zhibing Zhou, Zhen-Lin Hou, Fan Yang, Bo Yao The first oxidative cross-coupling of allylsilanes with aryl boronic acids has been developed by palladium catalysis. The reaction between β-substituted allyl(trimethyl)silanes and a wide range of aryl boronic acids afforded allylarenes in moderate to good yields and excellent selectivity. On the basis of experimental results and literature reports, it was suggested that the reaction might start from transmetalation of aryl boronic acid with AgOAc followed by transmetalation with Pd(II) to give an arylpalladium acetate complex as a key intermediate. This intermediate underwent either electrophilic addition/desilylation or transmetalation with allylsilane and subsequent reductive elimination to give the final product.Graphical abstractImage 1
       
  • A domino approach to pyrazino- indoles and pyrroles using vinyl selenones
    • Abstract: Publication date: Available online 26 October 2018Source: TetrahedronAuthor(s): Martina Palomba, Luca Sancineto, Francesca Marini, Claudio Santi, Luana Bagnoli Herein we disclose an efficient and flexible approach to biologically relevant 3,4-dihydropyrazino[1,2-a]indol-1(2H)ones and 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)ones through a domino Michael/intramolecular nucleophilic substitution pathway using potassium hydroxide in dichloromethane. Variously substituted vinyl selenones and 1H-indole-2-carboxamides or 1H-pyrrole-2-carboxamides have been employed with success in chemo and regio-selective processes. The introduction of an amino acid portion on the amidic function is well tolerated without racemization.Graphical abstractImage 1
       
  • Three novel Cu(II), Cd(II) and Cr(III) complexes of
           6−Methylpyridine−2−carboxylic acid with thiocyanate: Synthesis,
           crystal structures, DFT calculations, molecular docking and α-Glucosidase
           inhibition studies
    • Abstract: Publication date: Available online 26 October 2018Source: TetrahedronAuthor(s): Davut Avcı, Sümeyye Altürk, Fatih Sönmez, Ömer Tamer, Adil Başoğlu, Yusuf Atalay, Belma Zengin Kurt, Necmi Dege Novel complexes of 6−methylpyridine−2−carboxylic acid and thiocyanate {[Cu(NCS)(6-mpa)2], (1); [Cd(NCS)(6-mpa)]n, (2); [Cr(NCS)(6-mpa)2·H2O], (3)} were synthesized, and their structures were characterized by XRD analysis, FT–IR and UV–Vis spectroscopic techniques. The inhibitory activities of the synthesized complexes (1–3) on α-glucosidase were determined by using genistein reference compound. Furthermore, the optimized geometry and vibrational harmonic frequencies for the complexes 1–3 were obtained by DFT/HSEh1PBE/6–311G(d,p)/LanL2DZ level. Electronic spectral properties were examined by using TD-DFT/HSEh1PBE/6–311G(d,p)/LanL2DZ level with CPCM model. Additionally, major contributions to the electronic transitions were determined via Swizard program. The refractive index, linear optical and non−nonlinear optical parameters of the complexes 1–3 were investigated at HSEh1PBE/6–311G(d,p) level. The docking studies of the complexes 1–3 to the binding site of the target protein (the template structure S. cerevisiae isomaltase are fulfilled. Lastly, natural bond orbital analysis was used to investigate inter- and intra-molecular bonding and interaction among bonds.Graphical abstractImage 1
       
  • Highly stereoselective construction of tetrahydroquinolines via cascade
           aza-Michael-Michael reaction: Formal [4+2] cycloaddition of
           β,γ-unsaturated α-ketoesters with 2-aminochalcones
    • Abstract: Publication date: Available online 25 October 2018Source: TetrahedronAuthor(s): Cong Duan, Yongqi Yao, Ling Ye, Zhichuan Shi, Zhigang Zhao, Xuefeng Li An efficient cascade aza-Michael-Michael sequence for the preparation of tetrahydroquinolines has been established. Three contiguous stereogenic centers are created with high levels of enantioselectivities (79–99% ee) and exclusive diastereoselectivities in the presence of a bifunctional squaramide. This approach is compatible with a broad range of β,γ-unsaturated α-ketoesters and 2-aminochalcones. Our protocol indicated that β-site of β,γ-unsaturated α-ketoester is an available pro-nucleophilic site.Graphical abstractImage 1
       
  • New efficient synthesis of 1H-imidazo-[4,5-c]quinolines by a sequential
           Van Leusen/Staudinger/aza-Wittig/ carbodiimide-mediated cyclization
    • Abstract: Publication date: Available online 25 October 2018Source: TetrahedronAuthor(s): Zhi-Rong Guan, Zi-Ming Liu, Ming-Wu Ding A new efficient synthesis of multisubstituted 1H-imidazo-[4,5-c]quinoline derivatives via sequential van Leusen/Staudinger/aza-Wittig/carbodiimide-mediated cyclization was developed. Azides 4, obtained from Van Leusen reaction of 2-azidobenzaldehyde 1, amine 2 and TosMIC (tosylmethyl isocyanide) 3, reacted with triphenyl phosphine to produce iminophosphorane 5. A tandem aza-Wittig reaction of iminophosphorane 5 with isocyanate generated 1H-imidazo-[4,5-c]quinoline 7 through carbodiimide intermediate 6 in moderate to good yield.Graphical abstractImage 1
       
  • Syntheses of thallusin analogues and their algal morphogenesis-inducing
           activities
    • Abstract: Publication date: Available online 24 October 2018Source: TetrahedronAuthor(s): Hirofumi Yamamoto, Yuichi Takagi, Naoto Yamasaki, Tadashi Mitsuyama, Yusuke Kasai, Hiroshi Imagawa, Yutaro Kinoshita, Naohiro Oka, Masanori Hiraoka Thallusin is the only known natural product that induces cell differentiation followed by formation of a thallus during the growth of green macroalgae such as Monostroma and Ulva. Herein, various thallusin analogues based on the terpen skeleton were synthesized to study the structure−activity relationships of thallusin. The potency of the synthetic analogues was investigated in an experimental assay, which demonstrated that the 19-methyl group in thallusin is essential for potent morphogenesis-inducing activity.Graphical abstractImage 1
       
  • Tosylmethylisocyanide (TosMIC) [3+2] cycloaddition reactions: A facile Van
           Leusen protocol for the synthesis of the new class of spirooxazolines,
           spiropyrrolines and Chromeno[3,4-c]pyrrols
    • Abstract: Publication date: Available online 24 October 2018Source: TetrahedronAuthor(s): Ahmad Shaabani, Heshmatollah Sepahvand, Ayoob Bazgir, Hamid Reza Khavasi The reactivity and chemo-, regio- and diastreo-selectivity of tosylmethyl isocyanides (TosMIC) are investigated in Van Leusen type [3 + 2] cycloaddition reactions with the various activate cyclic ketones and double CC bonds in the synthesis of spirooxazolines, spiropyrrolines and chromeno[3,4-c]pyrrols in good to excellent yields under catalyst-free conditions without any activation at ambient temperature.Graphical abstractImage 1
       
  • From imidates to vinyl-1,2,4-tiazoles: Synthesis, mechanistic aspects and
           first issues of their reactivity
    • Abstract: Publication date: Available online 24 October 2018Source: TetrahedronAuthor(s): Safa Azzouni, Abderrahmen Abdelli, Anne Gaucher, Youssef Arfaoui, Mohamed Lotfi Efrit, Damien Prim The reaction of variously substituted acylimidates with hydrazine derivatives represents an efficient and easy to set synthetic entry towards 5-vinyl-1,2,4-triazole derivatives. The construction of the triazole ring allows the installation of variety of substituent combination at the N(1), C(3) and C(5) positions of the five-membered heterocycle in good to high yields. The method reveals selective towards 5-vinyl-1,2,4-triazoles avoiding the potential formation of seven- and five-membered side-products as supported by theoretical calculations and NMR experiments. First lines of Pd-catalyzed arylation of the vinyl fragment towards 5-styryl-1,2,4-triazoles and Cu-catalyzed arylation at the N(1) site are finally described.Graphical abstractImage 1
       
  • Vinyl nosylates as partner in copper and silver co-catalyzed Sonogashira
           cross-coupling reactions
    • Abstract: Publication date: Available online 23 October 2018Source: TetrahedronAuthor(s): Nicolas P. Cheval, Barbara Hoffmann, Anna Dikova, Fatih Sirindil, Philippe Bertus, Aurélien Blanc, Jean-Marc Weibel, Patrick Pale Vinyl nosylates, readily obtained from β-dicarbonyl derivatives, could be efficiently engaged in Sonogashira cross-coupling reactions, either cocatalyzed by copper or silver salts. The para-nitrobenzenesulfonate (nosylate) group allows this coupling to be performed under very mild conditions (room temperature). These new leaving group and mild conditions could be applied to the synthesis of acetylenic coumarinyl derivatives and to the total synthesis of an acetylenic monoterpene natural product, named cleviolide.Graphical abstractImage 1
       
  • A novel fluorescent probe for formaldehyde based-on monomer-excimer
           conversion and its imaging in live cells
    • Abstract: Publication date: Available online 23 October 2018Source: TetrahedronAuthor(s): Baichuan Han, Jin Sun, Kai Chen, Zhiyong Chen, Minhua Huang, Zhenzhong Gao, Xianfeng Hou A novel fluorescent probe was developed for formaldehyde, which can be synthesized by one-step Buchwald–Hartwig reaction. When hydrazino-group of probe reacted with formaldehyde, hydrophobic reaction product aggregates into nanoparticles and results in the blue fluorescence due to the monomer-excimer effect. With enough sensitivity, high selectivity, good stability in physiological pH range and excellent biocompatibility, this probe can image formaldehyde in living cells.Graphical abstractImage 1
       
  • Study on the green click-chemistry synthesis of
           4-trifluoroacetyl-1,2,3-triazoles
    • Abstract: Publication date: Available online 23 October 2018Source: TetrahedronAuthor(s): Jie Han, Jian-Xiong Ran, Xiu-Ping Chen, Zhong-Hua Wang, Fan-Hong Wu A metal-free and solvent free click-chemistry procedure has been revealed for the synthesis of 4-trifluoroacetyl-1,2,3-triazoles from corresponding azides and alkyne with high yield and selectivity. The pure products could be easily obtained via crystallization of the reaction mixture (standing for 1 day). Among the 4-trifluoroacetyl-1,2,3-triazoles, 3ba showed the best anticancer activity against HepG2 cell with IC50 of 0.0267 μmol/ml. This method has the advantages of less pollution, low cost, simple treatment and more efficiency.Graphical abstractImage 1
       
  • An efficient PyAOP-based C 4-amination method for direct access of
           oxidized 5MedC derivatives
    • Abstract: Publication date: Available online 22 October 2018Source: TetrahedronAuthor(s): Xiu-An Zheng, Hua-Shan Huang, Rui Kong, Wei-Jie Chen, Shan-Shan Gong, Qi Sun In the past decade, synthetic oxidized 5-MedC nucleosides and their derivatives have become essential tools for epigenetic research. The low efficacy of both conventional and newly reported BOP methods on C4-amination of these specific oxidized 5-MedU substrates urged us to systematically investigate how the nature of onium salt-based coupling reagents affects the C4-amination of pyrimidine nucleobases and lead us to the findings that different onium coupling reagents result in the formation of distinctive activation intermediates and PyAOP is much more potent than BOP in both activation and aminolysis steps. Direct amination without the need of ribose protection, ultrafast activation, tolerance to aqueous N-nucleophiles, and excellent yields for diverse oxidized 5MedC derivatives are the advantages of this PyAOP-based C4-amination method.Graphical abstractImage 1
       
  • Rh(III)-catalyzed C-H activation of primary benzamides and tandem
           cyclization with cyclic 2-diazo-1,3-diketones for the synthesis of
           isocoumarins
    • Abstract: Publication date: Available online 22 October 2018Source: TetrahedronAuthor(s): Xinwei He, Guang Han, Youpeng Zuo, Yongjia Shang A simple and efficient Rh(III)-catalyzed C-H activation and tandem intramolecular cyclization for the synthesis of isocoumarins has been developed. The protocol uses easily available primary benzamides and cyclic 2-diazo-1,3-diketones as starting materials. This reaction proceeds via C-C and C-O bond formation in a single reaction vessel, and the corresponding isocoumarins were obtained in moderate to excellent yields (58%–97%). The well established protocol showed high functional group tolerance, which provided an efficient and alternative route to isocoumarin backbone.Graphical abstractImage 1
       
  • Asymmetric synthesis of 7-aza-phomopsolide E and its C-4 epimer
    • Abstract: Publication date: Available online 22 October 2018Source: TetrahedronAuthor(s): Alhanouf Z. Aljahdali, Seth A. Freedman, Miaosheng Li, George A. O'Doherty A flexible, enantioselective route to highly functionalized α,β-unsaturated δ-lactones has been applied to the synthesis of 7-aza-phomopsolide E and its C-4 epimer. This approach relies on the application of the Noyori asymmetric hydrogenation of furyl ketone to produce the secondary furyl alcohol in high enantioexcess, which can be stereoselectively transformed into α,β-unsaturated-δ-lactones by a short, highly diastereoselective oxidation and reduction sequence. DCC and acid chloride couplings were used to introduce the side chains of the two natural product analogs.Graphical abstractImage 1
       
  • Inclusion and selectivity of amides by p-terphenyl derivative bearing
           adamantanecarboxylic acid
    • Abstract: Publication date: Available online 21 October 2018Source: TetrahedronAuthor(s): Masatoshi Kawahata, Kiyoe Matsui, Tadashi Hyodo, Masahide Tominaga, Kentaro Yamaguchi Hydrogen-bonding compound (1), which is composed of p-terphenyl and adamantanecarboxylic acid, acted as a host molecule for three amides, respectively, forming crystals. Crystals containing the amides (1a and 1b) were produced from N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF) in 1:2 host:guest complexation stoichiometry, respectively, whereas guest-free crystals (1c) were generated from N-methylformamide (NMF). In the crystal structures of 1a and 1b, carboxylic acids of 1 interact with oxygen atoms of the amide guests through hydrogen bonds to afford network and layer architectures. Crystals 1a and 1b were given from equimolar binary mixtures of DMF or DEF and NMF, respectively. Further, from a mixture of DMF and DEF, guest-inclusion crystals 1d different from 1a and 1b were formed, where DMF was preferentially accommodated. Competition experiments revealed that the selectivity order of 1 for the amide guests was DMF > DEF ≫ NMF.Graphical abstractImage 1
       
  • Highly enantioselective Michael/cyclization tandem reaction between
           dimedone and isatylidene malononitriles
    • Abstract: Publication date: Available online 19 October 2018Source: TetrahedronAuthor(s): Jia-Long Hu, Feng Sha, Qiong Li, Xin-Yan Wu A highly enantioselective Michael/cyclization tandem reaction between dimedone and isatylidene malononitriles has been developed. With 5 mol% of bifunctional organocatalyst C15, chiral spiro[2-amino-4H-pyran-oxindole] derivatives were obtained in excellent yields (97–99%) with excellent enantioselectivities (up to > 99% ee).Graphical abstractImage 1
       
  • Synthesis and characterization of N-heterocyclic carbene complexes of
           1,3,2-dioxaborolane-4,5-dione (NHC-boryl oxalates)
    • Abstract: Publication date: Available online 19 October 2018Source: TetrahedronAuthor(s): Daniel A. Bolt, Steven J. Geib, Dennis P. Curran NHC-boranes react with oxalic acid in acetonitrile slowly at room temperature and rapidly at 80 °C to form NHC-boryl oxalates. For example, heating of 1,3-dimethylimidazol-2-ylidene borane with oxalic acid in acetonitrile (80 °C, 2 h) provides the cyclic NHC-boryl oxalate derived from two sequential acid/base reactions in 59% isolated yield. The new NHC-boryl oxalates are robust white solids that are formally complexes of 1,3,2-dioxaborolane-4,5-dione, itself an unknown heterocycle.Graphical abstractImage 1
       
  • Nickel-catalyzed regio- and stereoselective hydrophosphinylation of
           internal ynamides with H-phosphinates
    • Abstract: Publication date: Available online 19 October 2018Source: TetrahedronAuthor(s): Atsushi Kinbara, Haruka Kasai, Kaede Sato, Yuri Watanabe, Takehiro Yamagishi A method for the catalytic hydrophosphinylation of internal ynamides with H-phosphinates has been developed for the first time. The protocol employing the catalyst generated from NiBr2 and PPh3 could be applied to several types of ynamides and H-phosphinates, affording (E)-β-aminovinylphosphinates in a highly regio- and stereoselective manner.Graphical abstractImage 1
       
  • Synthesis of trisubstituted olefins via nickel-catalyzed decarboxylative
           hydroalkylation of internal alkynes
    • Abstract: Publication date: Available online 18 October 2018Source: TetrahedronAuthor(s): Xiao-Yu Lu, Jing-Song Li, Mei-Lan Hong, Jin-Yu Wang, Wen-Jing Ma A novel NiH-catalyzed decarboxylative hydroalkylation of internal alkynes has been developed. Trisubstituted olefins were obtained in moderate to good yields with good regioselectivities. The reaction involves cis addition of NiH to the internal alkyne. The reaction shows good functional-group tolerance.Graphical abstractImage 1
       
  • Indole-substituted 2,4-diamino-5,8-dihydropyrido[2,3-d]pyrimidines from
           one-pot process and evaluation of their ability to bind dopamine receptors
           
    • Abstract: Publication date: Available online 18 October 2018Source: TetrahedronAuthor(s): Ricardo D. Enriz, Rodrigo D. Tosso, Sebastián A. Andújar, Nuria Cabedo, Diego Cortés, Manuel Nogueras, Justo Cobo, Didier F. Vargas, Jorge Trilleras A series of novel 7-indole substituted 2,4-diamino-5,8-dihydropyrido[2,3-d]pyrimidine analogous to the 2,4-diaminopteridine core were synthesized by the three-component one-pot cyclocondensation between 2,4,6-triaminopyrimidine, 3-(2-cyanoacetyl)indole and aromatic aldehydes. The reactions, which exhibited good performance, proceeded in EtOH using indium (III) chloride as catalyst under microwave irradiation, in short reaction times. On the basis of certain structural similarity of these compounds with known ligands of the D2 dopamine receptors (D2DR), the study of these compounds as possible ligands of dopamine D2 and D1 receptors was carried out. Three of them showed moderate affinity to D2-DR since the Ki D1/D2 ratio reached values of 40, 65 and 31 for compounds 4c, 4k and 4j, respectively. Finally, molecular modeling studies revealed stronger molecular interactions of such derivatives with the D2DR than with D1DR, what agrees with the experimental data, and gives an additional support to the observed selectivity to the D2DR.Graphical abstractImage 1
       
  • Synthesis and structure revision of litseaone A
    • Abstract: Publication date: Available online 18 October 2018Source: TetrahedronAuthor(s): Hideaki Kageji, Naoki Mori, Hirosato Takikawa, Hidenori Watanabe Litseaone A, isolated from the stem barks of Litsea rubescens and Litsea pedunculata, is a chalcone derivative with a novel spiro-epoxide moiety. The structural revision of litseaone A was achieved by the racemic synthesis of the proposed structure and the asymmetric synthesis of the revised structure. The major tautomeric structure of litseaone A and the relative stereochemistry at the epoxide carbon center were also clarified.Graphical abstractImage 1
       
  • From isonitrile to nitrile via ketenimine intermediate:
           Palladium-catalyzed 1,1-carbocyanation of allyl carbonate by
           α-isocyanoacetate
    • Abstract: Publication date: Available online 18 October 2018Source: TetrahedronAuthor(s): Guanyinsheng Qiu, Charlotte Sornay, David Savary, Sheng-Cai Zheng, Qian Wang, Jieping Zhu A palladium-catalyzed 1,1-carbocyanation of allyl carbonate by α-quaternary α-isocyanoacetate was developed. Formation of ketenimine followed by homolysis of the C-N bond and recombination of the resulting caged radical pair was proposed to account for the formation of the unusual coupling product, the β-cyano-γ,δ-unsaturated ester.Graphical abstractImage 1
       
  • Synthesis of zinc 20-ethenylated bacteriochlorophyll-d analogs and their
           self-aggregation in an aqueous micelle solution
    • Abstract: Publication date: Available online 17 October 2018Source: TetrahedronAuthor(s): Hitoshi Tamiaki, Ayaka Wada, Masashi Kishi Zinc complexes of 3-hydroxymethyl-131-oxo-chlorins possessing a vinyl or its trans-substituted group at the 20-position were prepared through regioselective bromination and successive palladium-catalyzed cross-coupling reactions from naturally occurring chlorophyll-a. The synthetic zinc chlorophyll-a derivatives self-aggregated in an aqueous Triton X-100 micelle solution to give red-shifted and broadened electronic absorption bands, which were similar to those of bacteriochlorophyll-c/d self-aggregates in the main light-harvesting antenna systems of green photosynthetic bacteria. Because of the sterically demanded perpendicular orientation of the (un)substituted ethenyl group to the chlorin π-system, the present model compounds had less J-aggregation ability in a slipped π–π interaction fashion than the corresponding saturated ethyl-type analogs, while halogenations at the terminal of the 20-vinyl group enhanced the ability due to their electron-withdrawing effect.Graphical abstractImage 1
       
  • Synthesis and photophysical properties of
           azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-diones: Azulene
           analogs of tryptanthrin
    • Abstract: Publication date: Available online 17 October 2018Source: TetrahedronAuthor(s): Chieko Kogawa, Asuka Fujiwara, Ryuta Sekiguchi, Taku Shoji, Jun Kawakami, Masaaki Okazaki, Shunji Ito Azulene analog of tryptanthrin, azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-dione, was successfully prepared by the condensation reaction of azuleno[2,1-b]pyrrole-2,3-dione with isatoic anhydride in the presence of sodium hydride or diisopropylethylamine (DIPEA). Its 2-halo derivatives were also obtained in high yields by the condensation reaction with 5-haloisatoic anhydrides in the presence of DIPEA. Reactivity toward electrophilic reagents was revealed by halogenation with N-bromosuccinimide (NBS) or N-iodosuccinimide (NIS) to afford 12-halo derivatives in high yields. Among the halo derivatives, 2-iodo and 12-iodo derivatives were reactive enough to afford phenylethynyl derivatives under Pd-catalyzed Sonogashira cross-coupling conditions. Within the phenylethynyl derivatives, only 12-phenylethynyl derivative was transformed into its 1,1,4,4-tetracyanobutadiene (TCBD) derivative by the reaction with TCNE. Amphoteric redox properties of the novel azulene analogs of tryptanthrin were characterized by spectroscopic and voltammetric analyses.Graphical abstractImage 1
       
  • Synthesis of isochromans via Fe(OTf)2-catalyzed
           Oxa-Pictet–Spengler cyclization
    • Abstract: Publication date: Available online 17 October 2018Source: TetrahedronAuthor(s): Jimei Zhou, Chao Wang, Dong Xue, Weijun Tang, Jianliang Xiao, Chaoqun Li Fe(OTf)2 has been found to be an efficient catalyst for the Oxa-Pictet–Spengler cyclization reaction leading to isochromans. A series of substituted isochromans were obtained with good to excellent isolated yields by coupling β-arylethanols with aldehydes or ketals under the catalysis of 1 mol% of Fe(OTf)2 at 70 °C. Using a cheap, less-toxic catalyst with water as the only byproduct, this iron-catalyzed Oxa-Pictet–Spengler reaction can be considered environmentally-friendly and atom-economic.Graphical abstractImage 1
       
  • A convenient and mild cyclocondensation using water-soluble aldehydes in
           water
    • Abstract: Publication date: Available online 16 October 2018Source: TetrahedronAuthor(s): Taku Kitanosono, Soo Min Cho, Shū Kobayashi The use of negatively charged aluminosilicate layers and Lewis acidic cations embedded therein allowed efficient cyclocondensation of bisamines with water-soluble aldehydes to be achieved in water. The protocol does not involve acidic or reflux conditions, thereby avoiding undesired byproduct formation. The use of water as a reaction medium is indispensable to ensure high reaction yields.Graphical abstractTo create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered.Image 1
       
  • Synthesis and further transformations of 8-chloro-3,4-dihydroisoquinoline
    • Abstract: Publication date: Available online 11 October 2018Source: TetrahedronAuthor(s): Csilla Hargitai, Tamás Nagy, Judit Halász, Györgyi Koványi-Lax, Gábor Németh, Gyula Simig, Balázs Volk Two procedures for the synthesis of barely accessible 8-chloro-3,4-dihydroisoquinoline were investigated. The first approach is based on a directed ortho-lithiation of N-pivaloyl meta-chlorophenylethylamine, followed by formylation and subsequent ring closure under acidic conditions. In the second, more advantageous variant, the N-hydroxyethyl ortho-chlorobenzylamine intermediate undergoes a Friedel-Crafts reaction, and the resulting tetrahydro derivative is oxidized with N-bromosuccinimide. The 8-chloro-3,4-dihydroisoquinoline key intermediate is then applied in Suzuki reactions to give various 8-aryl-3,4-dihydroisoquinolines, which are finally treated with alkyl and aryllithiums to give 1-substituted 8-aryl-1,2,3,4-tetrahydroisoquinolines. These novel 1,2,3,4-tetrahydroisoquinoline derivatives can be used as building blocks in the synthesis of potential drug candidates.Graphical abstractImage 1
       
  • Isatin N-protected ketimines with nitromethane catalyzed by chiral binol
           linked monomeric macrocyclic Cu(II)–salen complex
    • Abstract: Publication date: Available online 2 October 2018Source: TetrahedronAuthor(s): Tusharkumar Menapara, Raj kumar Tak, S. Saravanan, Rukhsana I. Kureshy, Noor-ul H. Khan, B. Ganguly, Mrinal Kanti Si Chiral Cu-1B generated in situ was used as an efficient catalyst for the synthesis of β-nitroamines in high yield (88%) with excellent enantioselectivity (ee up to 99%) at RT in absence of co-catalyst via asymmetric aza-Henry reaction of various isatin derived N-Boc ketimines with nitromethane. This catalytic system did not work well with other nitroalkanes under the above optimized reaction conditions. To examine this catalytic behaviour, quantum chemical DFT calculations were performed with the nucleophiles (CH2NO2− and CH3CHNO2−) for the conversion of 1a to 2a using macrocyclic Cu-1B complex. The DFT calculated results have shown that the reaction with CH2NO2− is more favourable than the corresponding CH3CHNO2−. The calculated activation barriers suggest that the reaction with CH2NO2− is ∼8.0 kcal/mol energetically favoured than CH3CHNO2−. This catalytic protocol was further used to obtain chiral β-diamines (a building block for pharmaceuticals) at gram scale. In order to elucidate the reaction mechanism of asymmetric aza Henry reaction kinetic experiments were performed with different concentrations of the catalyst Cu-1B, nitromethane and 1g as the representative substrate. The reaction of isatin N-Boc ketimine was first order with respect to the concentration of the catalyst and the nitromethane but did not depend on the initial concentration of the substrate. A possible mechanism for the aza Henry reaction was proposed.Graphical abstractImage 1
       
  • Formal [4 + 1] cycloaddition strategy for the synthesis of
           dihydrobenzofurans via Michael addition of 2-(2-nitrovinyl)-phenols and
           malonate esters (C1 synthon) and subsequent iodine-catalyzed oxidative
           annulation
    • Abstract: Publication date: Available online 21 September 2018Source: TetrahedronAuthor(s): Jiaying Leng, Jiang Meng, Xiaoyan Luo, Wei-Ping Deng A novel [4 + 1] cycloaddition protocol for the synthesis of dihydrobenzo(naphtho)furan skeletons from readily available 2-(2-nitrovinyl)-phen(naphth)ols and malonate esters via a tandem Michael addition/iodine-catalyzed oxidative annulation has been developed. This method provides a new and facile application of malonate esters as 1,1-nucleophilic/electrophilic type C1 synthons without a pre-functionalization step and the plausible reaction mechanism is proposed.Graphical abstractImage 1
       
  • Efficient and facile strategy to substituted 2-aminothiazoles via ring
           opening of α-nitroepoxides
    • Abstract: Publication date: Available online 6 September 2018Source: TetrahedronAuthor(s): Yue Zhu, Qilin Wang, Haofan Luo, Guolin Zhang, Yongping Yu A novel and efficient reaction has been developed to synthesize a set of substituted 2-aminothiazoles from α-nitroepoxides and ammonium thiocyanate. This reaction could proceed smoothly at mild condition, to afford products for a wide range of substrates with good to excellent yields. A possible mechanism has also been proposed.Graphical abstractImage 1
       
 
 
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