Tetrahedron Asymmetry

Synthesis of [2.2]paracyclophane-based bidentate oxazoline–carbene ligands for the asymmetric 1,2-silylation of N-tosylaldimines ()
Publication date: Available online 26 May 2017 Source:Tetrahedron: Asymmetry Author(s): Xichao Wang, Zhen Chen, Wenzeng Duan, Chun Song, Yudao Ma A series of novel oxazoline-substituted imidazolium salts with planar and central chirality has been successfully synthesized and applied to copper-catalyzed enantioselective 1,2-silylation of N-tosylaldimines. The oxazoline–carbene copper complex generated in situ by the reaction of the oxazoline-substituted imidazolium and Cu2O demonstrated an exceptionally high catalytic activity in the asymmetric 1,2-silylation of N-tosylaldimines, affording chiral α-amino silanes with excellent yields and enantioselectivities. Graphical abstract image
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Chemo-enzymatic synthesis of (R)-5-hydroxymethyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate, a potential chiral building block for multicyclic terpenoids ()
Publication date: Available online 26 May 2017 Source:Tetrahedron: Asymmetry Author(s): Kazuaki Kuwata, Kengo Hanaya, Takeshi Sugai, Mitsuru Shoji The chemo-enzymatic synthesis of (R)-5-hydroxymethyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate, a potential chiral building block for polycyclic terpenoids containing a five–membered ring having isopropyl and angular methyl substituents, such as erinacin A and dolatriol, was achieved over 11 steps from ethyl 2-oxocyclopentane-1-carboxylate. The key synthetic precursor for this triflate was ethyl (1S,2R)-2-hydroxycyclopentanecarboxylate (>99% ee), which was prepared by a lipase-catalyzed enantioselective hydrolysis of the corresponding racemic acetate. The antipodal (S)-triflate is expected to be the synthetic intermediate for another group of terpenoids involving hamigeran B and stolonidiol. Enantiomerically pure (1R,2S)-hydroxyester (>99% ee) was prepared in high yield using the asymmetric reduction of the oxoester with commercially available carbonyl reductase, “Chiralscreen® OH”-E001. Graphical abstract image
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3-Menthoxybiphenyl-4-carboxylic acid: a versatile resolving agent and reagent for determination of the absolute configuration of benzylic alcohols ()
Publication date: Available online 26 May 2017 Source:Tetrahedron: Asymmetry Author(s): Shunsuke Kuwahara, Nobuyoshi Tasaki, Yuri Suzuki, Mizuki Nakagawa, Mari Ikeda, Yoichi Habata A versatile reagent for the chiral resolution and determination of the absolute configuration of benzylic alcohols, (−)-3-menthoxybiphenyl-4-carboxylic acid, is reported. (−)-3-menthoxybiphenyl-4-carboxylic acid was condensed with racemic benzylic alcohols to yield diastereomeric 3-menthoxybiphenyl-4-carboxylic esters, which were separated by reversed-phase HPLC. The absolute configurations of the 3-menthoxybiphenyl-4-carboxylic esters were unambiguously determined by exciton-coupled circular dichroism. Hydrolysis of the 3-menthoxybiphenyl-4-carboxylic esters yielded enantiopure alcohols, and their absolute configurations were simultaneously determined. Graphical abstract image
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A convenient stereoselective synthesis of 5-hydroxy-3-oxoesters and 3-hydroxy-5-oxoesters ()
Publication date: Available online 24 May 2017 Source:Tetrahedron: Asymmetry Author(s): Anna Żądło-Dobrowolska, Joerg H. Schrittwieser, Barbara Grischek, Dominik Koszelewski, Wolfgang Kroutil, Ryszard Ostaszewski A biocatalytic approach was employed for the asymmetric reduction of sterically demanding ketones to prepare 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates. Screening a collection of microorganisms led to the identification of stereocomplementary microbial strains that provide access to both enantiomers of 3-hydroxy-5-oxo-5-phenylpentanoates and 5-hydroxy-3-oxo-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). Moreover, the application of Saccharomyces cerevisiae gave two diastereomers of 3,5-dihydroxy-5-phenylpentanoates with high enantiomeric excess (up to 99% ee). The applicability of the identified strains was demonstrated by transforming the obtained dihydroxy ester into the chemically valuable lactone (4S,6R)-tetrahydro-4-hydroxy-6-phenyl-pyran-2-one. Graphical abstract image
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An improved synthesis of (20S)-camptothecin and its analogue via an asymmetric α-hydroxylation with a chiral organocatalyst ()
Publication date: Available online 23 May 2017 Source:Tetrahedron: Asymmetry Author(s): Xinlong Wang, Lingjun Xu, Fangjun Xiong, Yan Wu, Fener Chen An efficient and stereocontrolled synthesis of (20S)-camptothecin and an analogue has been developed. The key feature of this synthesis is the organocatalyzed asymmetric α-hydroxylation of the lactone precursor 4 to construct its stereocenter, providing tricyclic hydroxylactone 2 in 90% yield and with 88% enantioselectivity. The precursor 4 was efficiently synthesized from the known pyridine 5 in three steps. Graphical abstract image
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A planar chiral six-membered cyclic (amino)(ferrocenyl)carbene and its sulfur adduct ()
Publication date: Available online 23 May 2017 Source:Tetrahedron: Asymmetry Author(s): Risa Yasue, Masaru Miyauchi, Kazuhiro Yoshida A planar chiral ferrocene-fused cyclic aldimine was synthesized and a series of iminium salts were divergently prepared from it. The new carbene was generated from a salt by simple deprotonation with a strong base and identified by a carbene trapping experiment with sulfur. The sulfur adduct was fully characterized and its crystal structure implied that the new carbene would create an excellent chiral environment when used as a catalyst or a ligand in catalytic asymmetric synthesis. Graphical abstract image
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Study of a new ‘chiral proton’ organocatalyst with hydrolase activity: application in azlactone racemic dynamic resolution ()
Publication date: Available online 22 May 2017 Source:Tetrahedron: Asymmetry Author(s): Ángel L. Fuentes de Arriba, Omayra H. Rubio, Luis Simón, Victoria Alcázar, Laura M. Monleón, Francisca Sanz, Joaquin R. Morán For the first time, a 1,3-ketoenol system is described as an acid catalyst with hydrolytic activity. The combination of an enol and a pyridine/benzimidazole supported on a benzofuran skeleton allowed the creation of a novel bifunctional organocatalyst, which has been applied in azlactone racemic dynamic resolution. In spite of the moderate enantioselectivities obtained, the catalyst constitutes a novel concept in the field of chiral Brønsted acid catalysis. Graphical abstract image
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Asymmetric biosynthesis of intermediates of anti-HIV drugs ()
Publication date: Available online 19 May 2017 Source:Tetrahedron: Asymmetry Author(s): Yiyuan Wang, Yingxiu Cao, Yuanxiu Li, Jiayu Jin, Jinliang Li, Hao Song Human immunodeficiency virus (HIV) infection is the fifth most common cause of death and many new HIV infections occur every year. The prevalence of HIV also seriously affects the quality of a patient’s life. More than forty anti-HIV drugs have been put into clinical uses, many of which are chiral molecules with multiple stereogenic centers, for example abacavir, lamivudine, zidovudine, stavudine, tenofovir, atazanavir. However, the chemical synthesis of these chiral intermediates have the disadvantages of low enantiomeric purity and complex synthetic steps. The benefits of asymmetric biosynthesis of chiral drugs include high enantiomeric excess (e.e.), good product selectivity, mild reaction conditions, and less side effects. The biosynthesis of the chiral intermediates of these anti-HIV drugs is thus particularly important. Herein, we review the different sources of enzymes and microbial cells for the asymmetric biosynthesis of the above chiral anti-HIV drug intermediates. We also review recent biotechnology progress in engineering these enzymes and microbial cells with improved biocatalytic activities, including enzyme and cell immobilization, surface display of enzymes, and directed evolution of enzymes. These biotechnology processes enable the efficient biosynthesis of these chiral intermediates, facilitating the industrial production of anti-HIV drugs with reduced costs. Graphical abstract image
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Enzyme mediated kinetic resolution of δ-hydroxy-α,β-unsaturated esters as a route to optically active δ-lactones ()
Publication date: Available online 19 May 2017 Source:Tetrahedron: Asymmetry Author(s): Dominik Koszelewski, Daniel Paprocki, Anna Brodzka, Ryszard Ostaszewski A novel synthetic route to optically active saturated and unsaturated δ-lactones based on enzymatic kinetic resolution and ring-closing metathesis reactions has been proposed. The influence of temperature, co-solvent, organic additives and the substrate structure on the catalytic behavior of selected hydrolases was studied. The substantial impact of the organic co-solvent and surfactant type on the enzymatic activity and enantioselectivity was observed providing enantiomerically pure δ-hydroxy-α,β-unsaturated esters. The established protocol combining enzymatic kinetic resolution with ring closing metathesis was successfully applied in the synthesis of the enantiomerically pure (6R)-phenyl-5,6-dihydro-2H-pyran-2-one which plays crucial role in the synthesis of the number of bioactive compounds. Graphical abstract image
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Stereoselective Michael-alkylation and Michael-oxidation reactions of chiral 1,3-dioxolanones ()
Publication date: Available online 19 May 2017 Source:Tetrahedron: Asymmetry Author(s): Hao-Chun Liao, Kuan-Jen Yao, Yi-Chou Tsai, Biing-Jiun Uang A highly diastereoselective Michael-alkylation/oxidation methodology has been developed for the synthesis of optically active α-hydroxy-1,5-diester subunits. Inverse stereochemistry at the C2′ position could be achieved by using a Michael acceptor equipped with a suitable group followed by a highly stereoselective protonation. This methodology has been applied to the enantioselective synthesis of the upper fragment of (+)-retusine. Graphical abstract image
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2-Cyano-2-indolylpropanoic acid as a chiral derivatizing agent for the absolute configuration assignment of secondary alcohols and primary amines by 1H NMR and VCD ()
Publication date: Available online 19 May 2017 Source:Tetrahedron: Asymmetry Author(s): Claudia I. Bautista-Hernández, Nayely Trejo-Carbajal, Erick A. Zúñiga-Estrada, Alberto Aristeo-Dominguez, Myriam Meléndez-Rodríguez, Oscar R. Suárez-Castillo, Maricruz Sánchez-Zavala, Julián Cruz-Borbolla, Martha S. Morales-Ríos, Pedro Joseph-Nathan A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of 1H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a chiral derivatizing agent is presented. DFT calculations were carried out to demonstrate the anisotropic effect of the indole skeleton on the chiral alcohol or the amine fragment. Vibrational circular dichroism (VCD) measurements of the above series indicated a VCD bisignated couplet resulting from the interaction of the ester carbonyl group and the CN group. The absolute configuration assignments were further tested by X-ray diffraction analysis. Graphical abstract image
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Synthesis of the enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene, one of the major components of the sex pheromone of Ectropis oblique Prout ()
Publication date: Available online 19 May 2017 Source:Tetrahedron: Asymmetry Author(s): Jie Yu, Feng Guo, Yun-Qiu Yang, Hui-Hui Gao, Ru-Yan Hou, Xiao-Chun Wan Both enantiomers of (3Z,9Z)-cis-6,7-epoxy-3,9-octadecadiene, one of which is the major component of the sex pheromone of Ectropis oblique Prout, were synthesized in 23% overall yield for the (−)-(6S,7R)-enantiomer and 18% yield for the (+)-(6R,7S)-isomer. This protocol uses a sequential regioselective ring-opening strategy and provides a convenient and reliable access to other structurally related insect sex pheromones. Preliminary biological studies revealed that (−)-(6S,7R)-2a was roughly as active as the natural pheromone, while racemic (±)-2 was less bioactive and (+)-2b was much less bioactive. Graphical abstract image
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Editorial board ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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Graphical contents list ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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Contributors to this issue ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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Current applications of organocatalysts in asymmetric aldol reactions: An update ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5 Author(s): Majid M. Heravi, Vahideh Zadsirjan, Mahzad Dehghani, Nastaran Hosseintash The aldol reaction is one of the most important carbon–carbon bond formations in synthetic organic chemistry. An enantioselective aldol reaction should provide an enantioenriched product. The organocatalytic asymmetric aldol reaction via an in situ generated enamine intermediate is one of the most powerful synthetic tools to achieve enantiomerically pure products. This approach is often used to obtain chiral β-hydroxycarbonyl compounds with excellent enantioselectivity. In this report, we update our previous review regarding the applications of organocatalysts in asymmetric aldol reactions leading to chiral β-hydroxycarbonyl compounds as versatile synthetic motifs frequently found in pharmaceutically desired intermediates and biologically active naturally occurring compounds. Graphical abstract image
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Recent advances in asymmetric multicomponent reactions (AMCRs) ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5 Author(s): Tahereh Ahmadi, Ghodsi Mohammadi Ziarani, Parisa Gholamzadeh, Hoda Mollabagher Asymmetric multicomponent reactions (AMCRs) include the reaction of three or more reactants simultaneously to produce chiral products that they have some advantages containing simple procedures, saving time and energy, and being environmentally friendly processes. AMCRs have seen much development and their potent synthetic approaches are discussed in this review. Graphical abstract image
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Short syntheses of (−)-clavaminol A and deacetyl (+)-clavaminol H ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5 Author(s): Tian Jin, Lu Zhao, Maolin Huang, Yan Yue, Zhe-Bin Zheng, Won-Hun Ham Concise stereoselective syntheses of (−)-clavaminol A and deacetyl (+)-clavaminol H have been achieved from simple starting materials. Highlights of the synthesis for (−)-clavaminol A include a highly diastereoselective chelation-controlled hydride reduction of an amino ketone to give the anti amino alcohol directly, and NaBH4-mediated dehalogenation. The main synthetic approach for deacetyl (+)-clavaminol H features a highly diastereoselective chelation-controlled hydride reduction of the amino ketone to construct the anti amino alcohol and a palladium catalyzed hydrogenation reaction at the final step. Graphical abstract image
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Plant-mediated asymmetric reduction of 1-(3,4-dimethylphenyl)ethanone ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5 Author(s): Dubravko Pavoković, Renata Buđa, Fran Andrašec, Marin Roje, Marina Cvjetko Bubalo, Ivana Radojčić Redovniković Bioreduction mediated by plants is a highly selective and environmentally friendly approach to synthesise optically active alcohols. Herein the bioreduction of 1-(3,4)-dimethylphenyl)ethanone to the corresponding chiral alcohol 1-(3,4-dimethylphenyl)ethanol has been evaluated using nine different vegetables roots as biocatalysts. The chiral alcohol was prepared in yields ranging from 44.1% to 88.2%, and with enantiomeric excess up to 97.2% for the (S)-enantiomer. Sugar beet was the most promising among the tested vegetables roots. Therefore, sugar beet cell cultures (normal and transformed) were obtained and tested for the reduction as well, yielding the corresponding alcohol in the range from 62.1% to 88.2% yield and with enantiomeric excesses of >99%. Based on these results reported, there are no profound differences in the reductive capacity of undifferentiated cells and organs of the same plant species (sugar beet). Due to overall advantages of using cell cultures, we have highlighted this approach as a promising method for preparation of enantiomerically pure 1-(3,4-dimethylphenyl)ethanol. Graphical abstract image
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Resolution, absolute configuration and antifilarial activity of coumarinyl amino alcohols ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5 Author(s): Priyanka, Sweta Misra, Shailja Misra-Bhattacharya, Ray J. Butcher, Diksha Katiyar The resolution of racemic coumarinyl amino alcohols 5–10 was achieved by using the inexpensive and readily accessible chiral resolving agent N-carbethoxy-l-proline (S)-11. Direct esterification of rac-5–10 with (S)-11 furnished diastereomeric esters, which were easily separated by column chromatography. The obtained diastereomers yielded the desired enantiopure coumarinyl amino alcohols (S)-(+)-5–10 and (R)-(−)-5–10 in good yields with high enantiomeric excess on saponification. The absolute configurations were determined by X-ray crystal analysis and/or by comparison of the specific rotations. Furthermore, in in vitro antifilarial motility inhibition assays, enantiopure coumarins (S)-(+)-9, (R)-(−)-9 and (S)-(+)-10, (R)-(−)-10 were found to be less efficient in affecting the viability of macrofilariae of Brugia malayi than their racemic forms 9 and 10, respectively, indicating the synergistic effect of the enantiomers in evoking antifilarial action. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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Cumulative author index ()
Publication date: 15 May 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 5
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A carbohydrate-derived trifunctional scaffold for DNA-encoded libraries ()
Publication date: Available online 5 May 2017 Source:Tetrahedron: Asymmetry Author(s): Amalia M. Estévez, Felix Gruber, Alexander L. Satz, Rainer E. Martin, Hans Peter Wessel For the generation of DNA-encoded libraries, a central scaffold containing three exit vectors with defined chirality was devised starting from commercially available tri-O-acetyl-glucal. This scaffold may be connected to the DNA barcode at any of the three different exit vectors, thus making it a versatile approach as this readily leads to three different libraries. For one of the three possibilities, the compatibility with the DNA tag was demonstrated. The reactions include amide bond formation, Boc deprotection, urea formation, azide reduction and reductive alkylation. Graphical abstract image
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Copper(II) complexes of 2-(pyridine-2-yl)imidazolidine-4-thione derivatives for asymmetric Henry reactions ()
Publication date: Available online 5 May 2017 Source:Tetrahedron: Asymmetry Author(s): Gabriela Nováková, Pavel Drabina, Jan Svoboda, Miloš Sedlák The preparation of a new series of 2-(pyridine-2-yl)imidazolidine-4-thione derivatives is described. Their corresponding copper(II) complexes were found to be highly enantioselective catalysts for asymmetric Henry reactions (up to 98% ee). Immobilization of these complexes by anchoring onto Merrifield™ resin with respect to their use as recyclable catalysts was subsequently performed. The heterogeneous catalysts prepared in this way were tested in the asymmetric Henry reactions and showed high catalytic activity; they can be easily recycled, although their enantioselectivities were only moderate (∼50% ee). Graphical abstract image
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Editorial board ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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Graphical contents list ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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Contributors to this issue ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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A review on the synthetic approaches of rivaroxaban: An anticoagulant drug ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Tanzeela Abdul Fattah, Aamer Saeed Rivaroxaban is an effective and potent oral anti-coagulant drug approved by US FDA in 2008 and is widely used in the treatment of thromboembolic ailments, deep venous thrombosis, pulmonary embolism, myocardial infarction, cerebral stroke, angina pectoris, and transitory ischemic attacks. This review comprehensively provides an overview of the various asymmetric synthetic methods employed for the synthesis of rivaroxaban in high yields and stereoselectivity describing the various chiral synthons used in the synthetic process along with pros and cons of each method. In addition, methods for the industrial production of rivaroxaban have been highlighted in the manuscript. Graphical abstract image
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Synthesis of chiral aza-bis(oxazolines) derived from (+)-camphor ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Jaime González, Diego Martínez-Otero, Bernardo A. Frontana-Uribe, Erick Cuevas-Yañez Two novel chiral structurally azabis(oxazoline) ligands were synthesized using (+)-camphor as the starting material. Each of the ligands was prepared through the corresponding aminoalcohols. The structures of some crystalline derivatives were unambiguously established by X-ray analysis. Graphical abstract image
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Solvent free, fast and asymmetric Michael additions of ketones to nitroolefins using chiral pyrrolidine–pyridone conjugate bases as organocatalysts ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Chandan K. Mahato, Mrinalkanti Kundu, Animesh Pramanik New chiral organocatalysts are envisaged based on a pyrrolidine–pyridone conjugate and synthesized from commercially available proline employing standard protocols. These catalysts were found to be useful for asymmetric Michael additions of ketones to nitroolefins to afford the desired products in very good yields (up to 98%) with excellent diastereo- and enantioselectivities (>97:3 syn/anti and up to 98% ee) in very short reaction time compared with the existing reports. Graphical abstract image
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Acylative kinetic resolution of racemic aromatic β-hydroxy esters catalyzed by chiral nucleophilic N-(1-arylethyl)benzoguanidines ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Akira Yamada, Kenya Nakata, Isamu Shiina An efficient acylative kinetic resolution of racemic aromatic β-hydroxy esters with cyclohexanecarboxylic anhydride was achieved using newly designed (R)-N-methylbenzoguanidine ((R)-NMBG) derivatives. A series of (R)-NMBG derivatives was synthesized by modifying the original (R)-NMBG catalyst with the introduction of branched N-substituents containing a stereogenic center, and their catalytic performance was evaluated. (R,R)-N-(1-(β-1-Naphthyl)ethyl)benzoguanidine [(R,R)-NβNpEtBG] was found to function as an efficient acyl transfer catalyst for the reaction of a broad variety of substrates, regardless of the substituent type and substitution pattern. Graphical abstract image
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Pd-catalyzed enantioselective C–H arylation of phosphinamides with boronic acids for the synthesis of P-stereogenic compounds ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Yuan-Hui Chen, Xu-Long Qin, Jing Guan, Zhi-Jun Du, Fu-She Han A Pd-catalyzed enantioselective C–H arylation of phosphinamides with aryl boronic acids is presented. With readily affordable amino acid derivatives as chiral ligands, the reaction proceeded efficiently to afford the P-stereogenic phosphinamides in up to 75% yield and with 99% ee under mild conditions. Most importantly, the reaction could be performed on a large scale for various substrates. This method provides an alternative and reliable way for accessing P-stereogenic phosphinamides. Graphical abstract image
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New N,N-diamine ligands derived from (−)-menthol and their application in the asymmetric transfer hydrogenation ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Piotr Roszkowski, Jan.K. Maurin, Zbigniew Czarnocki Natural (−)-menthol was applied to construction of mono-N-tosylated-1,2-diamine derivatives. The O-tosylation and elimination of the tosylate of the menthol intermediate led to trans-p-menth-2-ene. The unsaturated menth-2-ene was next transformed into a mixture of N-tosylaziridines, which upon reaction with sodium azide gave four isomeric azides. The reduction of the formed tosylazides on Pd/C gave new chiral mono-N-tosylated-1,2-diamines, which were used as ligands in the asymmetric transfer hydrogenation protocol on aromatic ketones and endocyclic imine. Graphical abstract image
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1,1,1-Trifluoropropan-2-ammonium triflate enantiomers: stereoselective synthesis and direct use in reaction with epoxides ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Gemma Packer, Julien Malassis, Neil Wells, Mark Light, Bruno Linclau A three-step synthesis of enantiomerically enriched 1,1,1-trifluoro-2-propanamine based on the use of a chiral sulfinamide auxiliary is described. The reduction of the geometrically pure Z-sulfinimine (NOE, HOE) with NaBH4 or l-Selectride leads to the corresponding (R)- or (S)-configured amine derivatives (X-ray crystallographic analysis) with 92–96% de. The typical models to explain the stereoselection for these reducing agents fail to rationalize the obtained stereoselectivities, and an in situ imine isomerization is proposed to occur. The direct use of the hydrochloric acid salt (with excess Et3N) of this poorly nucleophilic amine for epoxide opening reactions is not possible due to the higher nucleophilicity of chloride. Hence, a novel triflate salt is introduced, synthesized through ready sulfinamide hydrolysis with trimethylsilyl triflate, which can be used directly, without the need of isolating the pure amine beforehand. Graphical abstract image
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Biotransformation of 3-azidomethyl-4-phenyl-3-buten-2-one and analogs by Saccharomyces cerevisiae: New evidence for an SN2′ mechanism ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Bruno R.S. de Paula, Dávila Zampieri, J. Augusto R. Rodrigues, Paulo J.S. Moran (Z)-3-XCH2-4-(C6H5)-3-buten-2-one enones (X=SCN, N3, SO2Me, OC6H5) were synthesized and submitted to biotransformations using whole Saccharomyces cerevisiae cells. The enone (X=SCN) produced (R)-4-(phenyl)-3-methylbutan-2-one (R)-6 with 93% ee and enones (X=N3, SO2Me, OC6H5) yielded a mixture of (R)-6 and the corresponding CC bond reduction products. Biotransformation with enone (X=N3) mediated by Saccharomyces cerevisiae resulted in two products via two different routes: (i) the ketone (R)-4-azido-3-benzylbutan-2-one in 28% yield and with >99% ee by CC bond reduction; (ii) ketone (R)-6 in 51% yield and with 95% ee via cascade reactions beginning with azido group displacement by the formal hydride from flavin mononucleotide in an SN2′ type reaction followed by reduction of the newly formed CC bond. Graphical abstract image
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Stereocontrolled self-assembly of luminescent lanthanide helicates and their enantiodifferentiation using Δ-TRISPHAT as the NMR resolving agent ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Ting Zhang, Guang-Lu Zhang, Li-Peng Zhou, Xiao-Qing Guo, Qing-Fu Sun Self-assembled supramolecular lanthanide constructs have great potential in luminescent bioprobes/sensors. Stereoselectivity on the lanthanide assemblies is needed to facilitate chiroptical probes and sensors. Herein we report the stereocontrolled synthesis of M2L3-type (M=metal ion, L=organic ligand) lanthanide triple-helicates using a chiral-induction strategy, where the periphery point-chirality [(R,R) or (S,S)] of the organic ligands was transferred into the metal centered chirality (ΔΔ or ΛΛ), thus leading to the formation of topological chiral (P or M) helicates. Moreover, commercially available Δ-TRISPHAT proved to be an effective NMR chiral resolving agent to differentiate between the two enantiomers of the helicate. Graphical abstract image
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Diastereoselective cycloaddition of (S)-N-(1-phenylethylimino)trifluoropropionate and trifluoroethylphosphonate with diazomethane ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Yuliya V. Rassukana, Ludmyla V. Bezgubenko, Oleg V. Stanko, Eduard B. Rusanov, Irina B. Kulik, Petro P. Onys'ko The cycloaddition reaction of (S)-(α-phenylethylimino)trifluoropropionate with diazomethane leads to a diastereomeric mixture (4.5:1) of 5-trifluoromethyl-1,2,3-triazoline-5-carboxylates. Enantiopure diastereomers were isolated by column chromatography and converted into their respective non-racemic 2-trifluoromethyl-aziridine-2-carboxylates and carboxylic acids. The absolute configuration of newly formed stereogenic centers was determined by XRD analysis. The stereoselective reaction between (S)-N-(α-phenylethyl)trifluoroacetimidoylphosphonate and diazomethane produces a diastereomeric mixture (2.5:1) of 5-trifluoromethyltriazoline-5-phosphonates readily separated by column chromatography in diastereomerically pure forms. Graphical abstract image
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Application of sulfonyl chlorides and chiral amines in the efficient synthesis of nonracemic sulfinamides ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Karolina Kamińska, Elżbieta Wojaczyńska, Jacek Skarżewski, Andrzej Kochel, Jacek Wojaczyński A simple protocol that allows the preparation of separable epimeric sulfinamides from chiral amines and sulfonyl chlorides reduced in situ with triphenylphosphine in the presence of KOH is described. Using this method, tosyl chloride and nosyl chloride were successfully reacted with α-substituted primary amines to give five diastereomeric pairs, in certain cases accompanied by a small amount of the corresponding sulfonamide. Enantiopure products were isolated by column chromatography. The obtained enantiomerically pure sulfinamides were tested as organocatalysts in the asymmetric epoxide ring opening. Graphical abstract image
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Asymmetric synthesis of 1,4-disubstituted 3-methylidenedihydroquinolin-2(1H)-ones ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Marlena Pięta, Jacek Kędzia, Jakub Wojciechowski, Tomasz Janecki A series of enantiomerically pure or highly enriched (R)- or (S)-3-methylidenetetrahydroquinolin-2-ones was readily prepared by highly diastereoselective Michael additions of various Grignard reagents to quinolin-2(1H)-ones, containing an (R,R)- or (S,S)-di(1-phenylethylamino)phosphoryl group as chiral auxiliary, followed by Horner-Wadsworth-Emmons olefination of formaldehyde. An efficient synthesis of the starting (R,R)- and (S,S)-3-({di[(1-phenylethyl)amino]}phosphoryl)-1-alkyl-quinolin-2(1H)-ones is also described. The relative and absolute configurations of the intermediate adducts and final methylidenequinolinones were established by NMR and X-ray analysis. Graphical abstract image
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Hydrolase-mediated resolution of the hemiacetal in 2-chromanols: The impact of remote substitution ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4 Author(s): Declan P. Gavin, Aoife Foley, Thomas S. Moody, U.B. Rao Khandavilli, Simon E. Lawrence, Pat O'Neill, Anita R. Maguire Hydrolase-catalysed dynamic kinetic resolutions of chroman-2-ol and 3-methyl chroman-2-ol can be effected with up to 88% conversion and 92% ee through the use of organic solvents. Extension to the resolution of the tolterodine precursor 1 proved more challenging. The presence of the remote phenyl substituent had a significant impact on the resolution and it was not possible to achieve high enantioselectivity together with efficient conversion from the focussed panel of enzymes screened. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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Cumulative author index ()
Publication date: 15 April 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 4
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Editorial board ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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Graphical contents list ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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Contributors to this issue ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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Evolution of synthetic routes towards homochiral Tapentadol ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Piotr P. Graczyk, Olga Zbrojkiewicz, Sven Nerdinger Analysis of the literature shows that the development of synthetic approaches to Tapentadol, an agonist of the μ-opioid receptor and norepinephrine reuptake inhibitor, has followed four, partially overlapping, phases. The most advanced approaches, based on stereoselective syntheses, appeared only after 2010. The majority of the chemistry examples presented in this review come from patent applications and as such have not been subjected to rigorous peer review, but may serve well as an inspiration to organic chemists for solving analogous synthetic problems. Graphical abstract image
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Enantioselective Michael addition of aldehydes to nitroolefins catalyzed by pyrrolidine-HOBt ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Togapur Pavan Kumar, Mohammad Abdul Sattar, Sthanikam Siva Prasad, Kothapalli Haribabu, Cirandur Suresh Reddy The oxytriazole catalyst “pyrrolidine-HOBt” developed for asymmetric Michael addition of cyclohexanone to nitroolefins is now evaluated for the asymmetric Michael addition of aldehydes to nitroolefins under similar reaction conditions. The results of this study indicate that, the oxytriazole catalyst “pyrrolidine-HOBt” is equally effective in promoting the Michael addition of aldehydes to nitroolefins on employing benzoic acid as an additive. The desired products, γ-nitrocarbonyl compounds were obtained in good yields and high enantioselectivities. Graphical abstract image
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Stereoselective synthesis of tacalcitol via (R)-MeCBS catalyzed borane reduction ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Hengrui Zhang, Wei Guo, Zhijie Fang A novel and efficient approach for the synthesis of 1α, 24(R)-dihydroxyvitamin D3 (tacalcitol) starting from readily available enone 1 has been achieved with high stereoselectivity. The key step involved in the synthesis of tacalcitol was the stereoselective reduction of enone 1 using borane as the reducing agent, and the effects of the critical reaction parameters such as temperature, various borane complexes have been examined. Finally, tacalcitol was obtained in five steps from enone 1 with an overall yield of 32% and a ratio of 24-R/S =95/5. Graphical abstract image
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