Tetrahedron Asymmetry

New N,N-diamine ligands derived from (−)-menthol and their application in the asymmetric transfer hydrogenation ()
Publication date: Available online 21 March 2017 Source:Tetrahedron: Asymmetry 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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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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S-Substituted-2-mercaptobenzthiazolium-based chiral ionic liquids: efficient organocatalysts for enantioselective sodium borohydride reductions of prochiral ketones ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Avtar Singh, Harish Kumar Chopra Novel chiral ionic liquids having chirality in their cationic part have been synthesized for evaluation of their catalytic potential as organocatalysts in sodium borohydride reduction of prochiral ketones to yield optically active secondary alcohols. The chiral ionic liquids have been synthesized from the reaction of (−)-menthol or (−)-borneol, chloroacetic acid and S-methyl/benzyl-2-mercaptobenzthiazole. The synthesized chiral ionic liquids have been characterized by 1H, 13C NMR and Mass spectrometry. Moderate to excellent enantiomeric excess (ee>99%) has been obtained in asymmetric sodium borohydride reduction of prochiral ketones using these salts as chiral catalysts. Graphical abstract image
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Synthesis of p-coumaroylquinic acids and analysis of their interconversion ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Anggy Lusanna Gutiérrez Ortiz, Federico Berti, Luciano Navarini, Angelo Monteiro, Marina Resmini, Cristina Forzato The synthesis of four isomers of p-coumaroylquinic acids was performed by esterification of p-acetylcoumaroylchloride with a suitably protected (−)-quinic acid. All isomers have been characterized by means of NMR spectroscopy and circular dichroism. Acyl migration was observed in the synthesis of 3-O-p-coumaroylquinic acid and 4-O-p-coumaroylquinic acid. Calculations on the most stable conformations of all isomers have also been performed to explain the acyl migration observed during the synthesis procedure. Graphical abstract image
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Silver-catalyzed diastereo- and enantioselective Michael additions of 2-oxazoline- and 2-thiazoline-4-carboxylate to nitroalkenes ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Akihiro Koizumi, Yukiko Matsuda, Ryosuke Haraguchi, Shin-ichi Fukuzawa The silver/ThioClickFerrophos (a chiral ferrocenyl P,S-ligand)-catalyzed Michael additions of 2-oxazoline- and thiazoline-4-carboxylate to nitroalkenes were highly anti-selective and enantioselective and produced the corresponding adducts in high yields. Graphical abstract image
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Efficient resolution of profen ethyl ester racemates by engineered Yarrowia lipolytica Lip2p lipase ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Doriane Gérard, Marc Guéroult, Leticia Casas-Godoy, Jean-Stéphane Condoret, Isabelle André, Alain Marty, Sophie Duquesne Enzyme-catalyzed enantiomer discrimination is still a great challenge for the development of industrial pharmaceutical processes. For the resolution of ibuprofen, naproxen and ketoprofen racemates, three major anti-inflammatory drugs, only lipases from Candida rugosa present a high selectivity if solvent and surfactant use is discarded. However, their catalytic activities are too low. In the present work, we demonstrate that the lipase Lip2p from the yeast Yarrowia lipolytica has a higher catalytic activity than C. rugosa lipases to hydrolyze the ethyl esters of ibuprofen, naproxen and ketoprofen, but its selectivity is not sufficient [E =52 (S); 11 (S) and 1.5 (R) respectively]. The enantioselectivity was further improved by site-directed mutagenesis, targeted at the substrate binding site and guided by molecular modelling studies. By investigating the binding modes of the (R)- and (S)-enantiomers in the active site, two amino acid residues located in the hydrophobic substrate binding site of the lipase, namely residues 232 and 235, were identified as crucial for enantiomer discrimination and enzyme activity. The (S) enantioselectivity of Lip2p towards ethyl ibuprofen esters was rendered infinite (E ≫300) by replacing V232 by an A or C residue. Substitution of V235 by C, M, S, or T amino acids led to a great increase in the (S)-enantioselectivity (E ≫300) towards naproxen ethyl ester. Finally, the variant V232F enabled the efficient kinetic resolution of ethyl ketoprofen ester enantiomers [(R)-enantiopreference; E ≫300]. In addition to the increase in selectivity, a remarkable increase in velocity by 2.6, 2.7 and 2.5times, respectively, was found for ibuprofen, naproxen and ketoprofen ethyl esters. Graphical abstract image
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Synthesis and crystal structure of (S)-pindolol ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Alexander A. Bredikhin, Zemfira A. Bredikhina, Alexey V. Kurenkov, Dmitry B. Krivolapov Racemic 3-(4-indolyloxy)-1,2-propanediol 2 has been effectively resolved into (S)- and (R)-enantiomers by a preferential crystallization procedure. Non-racemic (S)-2 was converted into (S)-4-(2,3-epoxypropoxy)-1H-indole (S)-4 via a Mitsunobu reaction and then into (S)-pindolol (S)-1. The crystalline (S)-1 was studied by single crystal X-ray diffraction. A large number of symmetry independent molecules (Z′=6) led to a weakening of the system of strong intermolecular hydrogen bonds, which combined with a loose packing (PI=64.6%), may be the cause of the abnormally low melting point of (S)-1 as compared with rac-1. Graphical abstract image
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Enantioselective synthesis of fatty acid amide hydrolase inhibitors with 1,3-disubstituted butan-2-one scaffold ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Tom R. Sundermann, Matthias Lehr Fatty acid amide hydrolase is a key enzyme in the inactivation of the analgesic and anti-inflammatory endocannabinoid anandamide. Previously, the chiral compound 1-(1H-benzotriazol-1-yl)-3-(4-phenylphenoxy)butan-2-one was identified as a potent inhibitor of fatty acid amide hydrolase and is therefore of interest as a potential agent against pain and inflammation. Two different approaches for the enantioselective synthesis of fatty acid amide hydrolase inhibitors with a 1,3-disubstituted butan-2-one scaffold were carried out. The first one uses the chiral epoxide 2-[1-(4-phenylphenoxy)ethyl]oxirane with an (R)- or (S)-configuration at the exocyclic stereocenter as central intermediates. These substances were obtained by separation of the non-stereoselectively synthesized epoxide into its racemic diastereomers by reversed phase chromatography followed by Jacobsen’s hydrolytic kinetic resolution of each enantiomer with the (S)-configured oxirane ring. Furthermore, a chiral pool based enantioselective synthesis was developed. In that case, the starting compound for both target enantiomers was methyl 3,4-O-isopropylidene-l-threonate. In comparison to the first approach, the chiral pool synthesis consisted of more steps, but generated the enantiomers with much better enantiomeric excess. Biological evaluation showed that the (R)-enantiomer inhibits isolated fatty acid amide hydrolase with a 200-fold higher activity than the (S)-enantiomer. Graphical abstract image
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Using enantioselective dispersive liquid–liquid microextraction for the microseparation of trans-cyclohexane-1,2-diamine enantiomers ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Majid Hashemi, Mohammad Reza Hadjmohammadi A new chiral separation system effective for the enantioselective extraction of racemic trans-cyclohexane-1,2-diamine is presented. Enantioselective dispersive liquid–liquid microextraction has been used for the chiral microseparation of trans-cyclohexane-1,2-diamine, with a chiral azophenolic crown ether being identified as a versatile chiral selector. The influence of various process conditions on the extraction performance was studied experimentally. It was found that the operational selectivity in one extraction step is mainly related to the type and volume of the solvents, chiral selector concentration, extraction time, temperature of sample solution, and pH. At optimum conditions (300μL of diethyl ether as the extraction solvent 1mL of methanol as the disperser solvent, with 5mmolL−1 chiral selector concentration, pH of the sample equal to 4.5, 30min extraction time and a temperature of 10°C), the distribution ratio of (R,R)- and (S,S)-trans-cyclohexane-1,2-diamine was 18.3 and 1.8, respectively, while the enantioselectivity value of 10.2 was found at the optimum condition. Graphical abstract image
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Solvent-induced chirality switching in the enantioseparation of regioisomeric hydroxyphenylpropionic acids via diastereomeric salt formation with (1R,2S)-2-amino-1,2-diphenylethanol ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Koichi Kodama, Jun Nagata, Nobuhiro Kurozumi, Hiroaki Shitara, Takuji Hirose The enantioseparation of three hydroxyphenylpropionic acid isomers via diastereomeric salt formation with (1R,2S)-2-amino-1,2-diphenylethanol has been demonstrated. The racemates of all three acid isomers were successfully separated with high efficiency (0.56–0.84) after single crystallization. For 2-hydroxy-3-phenylpropionic acid 4, the configuration of the less-soluble salt was controlled by the crystallization solvent: the (R)-4 salt was crystallized from water, while 2-propanol afforded the (S)-4 salt. The chiral recognition mechanism of the three acids was discussed based on the crystal structures of the diastereomeric salts. Graphical abstract image
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Chiral terpene auxiliaries IV: new monoterpene PHOX ligands and their application in the catalytic asymmetric transfer hydrogenation of ketones ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Anna Kmieciak, Marek P. Krzemiński New PHOX ligands, derived in three steps from (1R,2S,3R,5R)-3-amino-apopinan-2-ol 1 and (1R,2R,3S,5R)-3-amino-pinan-2-ol 2 were applied as chiral ligands for the formation of ruthenium catalysts. The catalysts were used in asymmetric transfer hydrogenations of prochiral ketones producing the corresponding alcohols in moderate to high yields and enantioselectivity. Graphical abstract image
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Enantioselective enzymatic resolution of racemic alcohols by lipases in green organic solvents ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Abderahmane Belafriekh, Francesco Secundo, Stefano Serra, Zeineddine Djeghaba The effects of two eco-friendly solvents, 2-methyltetrahydrofuran (MeTHF) and cyclopentyl methyl ether (CPME), on the enzyme activity and enantioselectivity of Novozym 435, Candida rugosa lipase (CRL), Porcine pancreas lipase (PPL), Lipase AK, Lipase PS, and Lipozyme, a series of commercial lipases, in the enantioselective transesterfications of racemic menthol, racemic sulcatol and racemic α-cyclogeraniol were studied. Vinyl acetate was chosen as the acyl donor and the reactions were carried out at water activity 0.06. The activity of lipases in CPME was similar to that observed in other largely employed organic solvents [toluene and tert-butyl methyl ether (MTBE)], and was slightly lower in MeTHF. However, for most of the lipases tested, the enantioselectivity was higher in the eco-friendly solvents. Lipase AK exhibited a high enantioselectivity (E =232) for the resolution of racemic menthol but the reaction rate was low. Lipase formulation (the enzyme was frozen and lyophilized in potassium phosphate buffer without and with 5% (w/v) of sucrose, d-mannitol, or methoxy poly(ethylene glycol)) was tested with this lipase in order to improve its activity, which increased up to 4.5 times, compared to the untreated enzyme. CALB was found to be a useful biocatalyst for the resolution of racemic sulcatol, where high activity and enantioselectivity were obtained (E ≥1000). For the resolution of the racemic primary alcohol α-cyclogeraniol, most of the lipases tested were active but not enantioselective, except lipase PS which displayed a moderate enantioselectivity (E =19). The effect of the presence of a low percentage of two ionic liquids (ILs) 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]) (5% (v/v)) and 1-Butyl-3-methylimidazoliumtetrafluoroborate ([BMIM][BF4]) (1% (v/v)) in the medium was also investigated. Only in the case of CRL the ILs slightly increased the enantioselectivity from E =91 to E =103 and E =120 for [BMIM][TFSI] and [BMIM][BF4], respectively. However, in all cases ILs caused a decrease of enzyme activity. Graphical abstract image
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Design, stereoselective synthesis and computational calculations of novel hybrid compounds via Pauson-Khand reactions ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3 Author(s): Selçuk Gümüş, Nezir Aslan, Nalan Nuriye Büyükadalı, Ayşegül Gümüş A series of novel chiral hybrid compounds between benzofuran and bicyclic cyclopentenone and also benzothiophene and bicyclic cyclopentenone have been designed and synthesized. Chiral enynes derived from enantiomerically enriched homoallyl and homopropargyl alcohols were converted into bicyclic cyclopentenone structures by intramolecular Pauson-Khand reactions. This strategy provides a facile access to various bicyclic cyclopentenones substituted with benzofuran or benzothiophene ring systems in good yields. In addition to the experimental work, the ground state geometries of the hybrid compounds were optimized using Density Functional Theory applications at the B3LYP/6-31G(d,p) level in order to obtain information about the 3D geometries and electronic structure. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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Cumulative author index ()
Publication date: 15 March 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 3
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A review on the synthetic approaches of rivaroxaban: An anticoagulant drug ()
Publication date: Available online 11 March 2017 Source:Tetrahedron: Asymmetry 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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Editorial board ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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Graphical contents list ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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Contributors to this issue ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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The role of hydrazide compounds in asymmetric synthesis ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Ghodsi Mohammadi Ziarani, Vaezeh Fathi Vavsari Asymmetric synthesis is one of the important topics in organic synthesis. Hydrazide compounds are valuable substrates in the fields of both chemical reactions and medicinal chemistry due to their chemical reactivity and biological activities, respectively. In this review, the role of hydrazides as substrates and/or chiral catalysts are investigated in the asymmetric organic reactions to gain chiral products. Graphical abstract image
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Stereoselective synthesis of modified cysteines ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Jaime Gracia-Vitoria, Iñaki Osante, Carlos Cativiela This review provides an overview of the literature concerning the stereoselective synthesis of a large group of modified cysteines. The different synthetic approaches are classified according to the bonds formed to build the cysteine backbone skeleton. Graphical abstract image
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First total synthesis of the highly potent antitumor lactones 8-chlorogoniodiol and parvistone A: Exploiting a bioinspired late-stage epoxide ring-opening ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Perla Ramesh, Yarram Narasimha Reddy, Thatikonda Narendar Reddy, Navuluri Srinivasu The first protecting group-free total syntheses of the highly potent antitumor chlorinated styryllactone secondary metabolites 8-chlorogoniodiol, parvistone A, and one analogue 8-epi-parvistone A, have been accomplished from commercially available trans-cinnamaldehyde in five steps with high overall yields. The chlorine-bearing stereogenic center of these silent secondary metabolites was introduced via a bioinspired late-stage regioselective epoxide ring-opening strategy. Maruoka asymmetric allylation, acrylation, ring-closing metathesis and asymmetric epoxidation, greatly facilitate the synthesis of the key intermediates goniothalamin oxide and (6S,7S,8S)-isogoniothalamin oxide. Graphical abstract image
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Assignment of the absolute configuration of hydroxy acids using 1H NMR spectroscopy: a simple and rapid approach ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Sandeep Kumar Mishra, N. Suryaprakash A simple, rapid and highly effective protocol for assigning the absolute configuration of various chiral α-hydroxy acids and their derivatives has been established by involving the coupling of 2-formylphenylboronic acid with (R)-[1,1-binaphthalene]-2,2-diamine, and 2-formylphenylboronic acid with (S)-[1,1-binaphthalene]-2,2-diamine as chiral derivatizing agents. The absence of aliphatic peaks from the derivatizing agent together with the large chemical shift separation between the discriminated diastereomer peaks, with a systematic change in the direction of the displacement of peaks for an enantiomer in a particular diastereomer complex, allows the unambiguous assignment of absolute configuration. Graphical abstract image
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Highly enantioselective Biginelli reactions using methanopyroline/thiourea – based dual organocatalyst systems: asymmetric synthesis of 4-substituted unsaturated aryl dihydropyrimidines ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Han Yu, Peng Xu, Huihong He, Jun Zhu, Hualin Lin, Sheng Han A series of novel chiral 3,4-dihydropyrimidin-2-(1H)-ones and -thiones (DHPMs) was developed via asymmetric Biginelli reactions catalyzed by a methanopyroline/thiourea – based dual organocatalyst system, providing excellent yield (90–96%) and high enantioselectivities (92–99% ee). Furthermore, novel epoxides with three stereogenic centers are disclosed, which might have application in the field of drugs and pharmaceuticals. Graphical abstract image
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Convenient synthesis of memantine analogues containing a chiral cyclopropane skeleton as a sigma-1 receptor agonist ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Tetsuya Ezawa, Yuya Kawashima, Takuya Noguchi, Seunghee Jung, Nobuyuki Imai We have achieved a convenient enantioselective synthesis of memantine analogues containing a chiral cyclopropane skeleton as a sigma-1 receptor agonist in 19–40% overall chemical yields from the corresponding 2-arylbut-2-ene-1,4-diols with moderate to excellent asymmetric yields via regioselective acetylation using porcine pancreas lipase, catalytic enantioselective Simmons-Smith reactions, and amidation in aqueous organic solvent. This synthetic route is more efficient and less expensive than conventional methods. Graphical abstract image
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Enantioselective chlorinative aldol reaction of α-substituted acroleins catalyzed by chiral phosphine oxides ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Shunsuke Kotani, Takuya Hanamure, Hirono Nozaki, Masaharu Sugiura, Makoto Nakajima The enantioselective chlorinative aldol reaction of α-substituted acroleins with aldehydes catalyzed by chiral phosphine oxides is described. A hypervalent silicon complex-derived chloride adds to the α-substituted acroleins to form the corresponding silyl enol ethers in situ, which subsequently reacts with aldehydes to produce the α-chloromethyl aldol adducts bearing a quaternary stereogenic center in good yields and stereoselectivities. When activated by a phosphine oxide catalyst, trichlorosilyl triflate acts as an effective promoter for the chlorinative aldol reaction as well as the chloride source; this discovery enabled the enantioselective chlorinative aldol reaction of α-substituted acroleins. Graphical abstract image
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Total syntheses of 9-epoxyfalcarindiol and its diastereomer ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Yun Zhou, Yanli Huang, Shuoning Li, Pengfei Yang, Jiangchun Zhong, Jingwei Yin, Kaijie Ji, Yanqing Yang, Ning Ye, Lifeng Wang, Mingan Wang, Min Wang, Qinghua Bian The first total syntheses of 9-epoxyfalcarindiol 1a and its diastereomer 1b have been achieved. Central to our approach were the Zn-cyclopropane-based amino alcohol catalyzed enantioselective alkynylation of acrolein, the diastereoselective addition of a diynic ester to an epoxy aldehyde, and the asymmetric Sharpless epoxidation of allylic alcohol catalyzed with L-(+)-diethyl tartrate and Ti(OiPr)4. Graphical abstract image
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Stereoselective E/Z-photoisomerization of cyclooctene using 2,4-pentanediol chiral tether ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Kuifeng Song, Morifumi Fujita, Tadashi Okuyama, Takashi Sugimura The photoisomerization, epoxidation, and cyclopropanation of chiral 2,4-pentanediol tethered cyclooctene were explored to examine the stereocontrollability of the tether. Photoisomerization of (2R,4R)-2,4-pentanediol-tethered cyclooctene achieved a de of 20% at a high Z/E ratio of 0.80 at 25°C, while (2S,4R)-2,4-pentanediol-tethered cyclooctene yielded a lower de in spite of an even higher Z/E ratio. The epoxidation and cyclopropanation of 2,4-pentanediol tethered cyclooctene resulted in lower stereoselectivity compared with those of vinyl ether. We propose that the low de of the reactions of 2,4-pentanediol tethered cyclooctene is not attributable to the low stereocontrollability of 2,4-pentanediol tether, but due to the conformational multiplicity of the reactant site. Graphical abstract image
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Organocatalytic enantioselective conjugate addition of aldehydes to maleimides in deep eutectic solvents ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Jesús Flores-Ferrándiz, Rafael Chinchilla The conjugate enantioselective addition of aldehydes, mainly α,α-disubstituted, to maleimides leading to enantioenriched succinimides, has been achieved in recyclable deep eutectic solvents at room temperature. Enantiomerically pure carbamate-monoprotected trans-cyclohexane-1,2-diamines are used as organocatalysts, affording high yields and up to 94% ee of the final succinimides. The product can be extracted from the deep eutectic solvent, which retains the chiral organocatalyst, allowing both the solvent and catalyst to be reused. Graphical abstract image
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An investigation towards the diastereoselective synthesis of 3-acetoxy/methoxy/phthalimido-β-lactams using chiral imines ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Aman Bhalla, Garima Modi, S.S. Bari, Anu Kumari, Dipika Narula, Shiwani Berry The efficient diastereoselective synthesis of 3-acetoxy/methoxy/phthalimido-β-lactams 2/2′, 3/3′ and 4/4′ respectively was performed using chiral imines 1 obtained from chiral amines. Factors (solvent, temperature, substituent, steric bulk) influencing the stereoselectivity and the diastereomeric ratio were also studied in detail. The diastereoselectivity of the two isomers was determined from the ratio of integral values of doublets of C3–H and C4–H and from the integral values of H in –CH(Me/Et)Ph/Np of the two diastereomers. Representative pairs of cis-diastereomers were separated by efficient column chromatography. Graphical abstract image
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‘On water’ organocatalyzed enantioselective synthesis of highly functionalized cyclohexanones with an all-carbon quaternary centre from allylidene malononitriles and enones ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Ganga B. Vamisetti, Raghunath Chowdhury, Mukesh Kumar, Sunil K. Ghosh An organocatalyzed endo [4+2] cycloaddition between enones as pro-diene and allylidene malononitrile as dienophile leading to cyclohexanones with two 1,3-related stereogenic centres and an all-carbon quaternary centre has been developed. The reactions were performed under ‘green reaction’ conditions using water as the reaction medium and ambient conditions. When allylidene cyanoacetate was used as the dienophile, cyclohexanones with three contiguous stereogenic centres, one of which is an all-carbon quaternary centre, were formed. The products were obtained in high yield and with acceptable diastereo- and enantioselectivity. Graphical abstract image
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Enantioselective synthesis of new chiral 2-aziridinyl phosphonates and studies of their biological activities ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Özdemir Dogan, Sıdıka Polat Çakır, Nurzhan Beksultanova, Nurten Altanlar, Duygu Şimşek, Hasan Karabıyık A new series of chiral aziridinyl phosphonates has been synthesized and evaluated for antibacterial and antifungal activities. For the synthesis, a Gabriel-Cromwell reaction was used to form aziridinyl phosphonates in 52–83% yield. In order to evaluate antibacterial and antifungal activities, MIC values were measured. Although most of the compounds showed insignificant activity, two of them provided low to moderate antifungal activity. Graphical abstract image
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Novel MOP-type H8-binaphthyl monodentate phosphite ligands and their applications in transition metal-catalyzed asymmetric 1,4-conjugate additions and hydroformylations ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Mi Tian, Zeng-bo Pang, Hai-feng Li, Lai-lai Wang A new series of monodentate phosphites based on the rigid, axially chiral monoesterified H8-BINOL, which are easy to prepare from the readily accessible phosphorylating reagents (S a)- or (R a)-1,1′-binaphthyl-2,2′-diylchlorophosphite and (S a)- or (R a)-1,1′-H8-binaphthyl-2,2′-diylchlorophosphite, have been synthesized. All ligands were purified on a silica gel column under a nitrogen atmosphere with moderate yields, and were white solids and air-stable at room temperature. These ligands afforded good to excellent enantioselectivities in the Cu-catalyzed 1,4-conjugate addition of 2-cyclohexenone with nucleophiles Et2Zn (96% ee) and with Ph2Zn (65% ee), 2-cyclopentenone with Et2Zn (95% ee), 2-cycloheptenone with Et2Zn (76% ee), and 5,6-dihydro-2H-pyran-2-one with Et2Zn (90% ee). In the Rh-catalyzed asymmetric hydroformylation of styrene, these ligands showed a chemoselectivity of >99% in aldehydes, and a satisfactory branched over linear ratio (96/4). Moreover, the sense of the enantiodiscrimination of the products was mainly determined by the configuration of the BINOL-based or H8-BINOL-based phosphocycle. Graphical abstract image
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Enantioselective synthesis of (2R,13R,8Z)-2,13-diacetoxy-8-heptadecene, the major component of the sex pheromone of the pear leaf midge, Dasineura pyri ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Yun Zhou, Pengfei Yang, Shuoning Li, Lifeng Wang, Jingwei Yin, Jiangchun Zhong, Yanhong Dong, Shangzhong Liu, Min Wang, Qinghua Bian The first enantioselective synthesis of (2R,13R,8Z)-2,13-diacetoxy-8-heptadecene 1, the major component of the sex pheromone of the pear leaf midge, Dasineura pyri, has been achieved. The key steps include the (R,R)-BINOL/Ti(OiPr)4 catalyzed alkynylzinc addition to an unsaturated aldehyde, the ring-opening of the chiral epoxide with a Grignard reagent, and the partial reduction of an acetylenic diol ester to a (Z)-olefinic diol ester with hydrogen and P2-Ni. Graphical abstract image
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Stereoselective de novo synthesis of (5R)-3,4:5,6-di-O-isopropylidene-d-ribo-hexos-5-ulo-5,2-furanose ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Estefanía Dibello, Leopoldo Suescun, Gustavo A. Seoane, Daniela Gamenara A concise and stereoselective de novo synthesis of the protected oxidized sugar (5R)-3,4:5,6-di-O-isopropylidene-d-ribo-hexos-5-ulo-5,2-furanose is described. The synthetic sequence involves a stereoselective proline-catalyzed aldol reaction of an orthogonally protected l-glyceraldehyde derivative and 2,2-dimethyl-1,3-dioxan-5-one, to obtain 5-O-acetyl-6-O-benzyl-1,3-isopropylidene-l-psicose as a key intermediate, and the final product in 5 steps and 38% yield. Graphical abstract image
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Synthesis of enantiopure cyclic amino acid derivatives via a sequential diastereoselective Petasis reaction/ring closing olefin metathesis process ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Veronika A. Morozova, Irina P. Beletskaya, Igor D. Titanyuk A novel approach to the synthesis of enantiopure cyclic amino esters is reported. The utilization of allylboronic acid together with (S)-α-methylbenzylamine as a chiral auxiliary in the Petasis/Mannich reaction led to the formation of allylglycine derivatives in good yield and with high diastereoselectivity. Subsequent esterification, N-allylation followed by ring-closing metathesis (RCM) reaction enabled the preparation of enantiomerically pure cyclic α-amino acid derivatives. Graphical abstract image
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Enantioselective NHC-catalysed redox [4+2]-hetero-Diels-Alder reactions using α-aroyloxyaldehydes and unsaturated ketoesters ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): James E. Taylor, Alyn T. Davies, James J. Douglas, Gwydion Churchill, Andrew D. Smith N-Heterocyclic carbene (NHC)-catalysed redox [4+2]-hetero-Diels-Alder reactions of α-aroyloxyaldehydes with either β,γ-unsaturated α-ketoesters or α,β-unsaturated γ-ketoesters generates substituted syn-dihydropyranones in good yield with excellent enantioselectivity (up to >99:1 er). The product diastereoselectivity is markedly dependent upon the nature of the unsaturated enone substituent. The presence of either electron-neutral or electron-rich aryl substituents gives excellent diastereoselectivity (up to >99:5 dr), while electron-deficient aryl substituents give reduced diastereoselectivity. In these cases, the syn-dihydropyranone products are more susceptible to base-promoted epimerisation at the C(4)-position under the reaction conditions, accounting for the lower diastereoselectivity obtained. Graphical abstract image
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The stereochemistry of the 1,3-dipolar cycloadditions of diazomethane to pseudoguaianolides ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Adriana Ortiz-León, J. Martín Torres-Valencia, J. Jesús Manríquez-Torres, José G. Alvarado-Rodríguez, Carlos M. Cerda-García-Rojas, Pedro Joseph-Nathan The 1,3-dipolar cycloaddition of diazomethane to the sesquiterpene lactones, parthenin, coronopilin, and psilostachyin, gave their respective spiropyrazolines with complete chemoselectivity, while the diastereoselectivity in favour of the (11S)-stereoisomer was 86–98%. Similarly, mexicanin I acetate, helenalin, and helenalin acetate provided the (11R)-diastereoisomer. When helenalin and its acetate were treated with a large excess of diazomethane, they afforded their respective dipyrazolines with 98% diastereoselectivity in favour of the (2R,3S,11R)-diastereoisomer. All compounds were characterized by their physical and spectroscopic properties and their absolute configuration was established by X-ray diffraction analysis calculating the Flack and Hooft parameters. Graphical abstract image
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Enantioseparation of (RS)-atenolol with the use of lipases immobilized onto new-synthesized magnetic nanoparticles ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): Adam Sikora, Dorota Chełminiak-Dudkiewicz, Marta Ziegler-Borowska, Michał Piotr Marszałł The enzymatic method was used for the direct resolution of racemic atenolol. The catalytic activities of commercially available lipases from Candida rugosa (MY and OF) immobilized onto new-synthesized chitosan magnetic nanoparticles [Fe3O4-CS-Et(NH2)2, Fe3O4-CS-Et(NH2)3] in the kinetic resolution of racemic atenolol were compared. The best results were obtained by using Candida rugosa lipase OF immobilized onto Fe3O4-CS-Et(NH2)3. Additionally, the enzyme reusability was investigated. It was established that even after 5 reaction cycles, both lipases from Candida rugosa maintained their high catalytic activities and operational stabilities. This approach is extremely important from an economical point of view, because it allows for a direct cost reduction of the biotransformation. Graphical abstract image
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Enantioselective alkylation of aromatic aldehydes with (+)-camphoric acid derived chiral 1,3-diamine ligands ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2 Author(s): M. Elisa Silva Serra, Dina Murtinho, Victória Paz A series of chiral 1,3-diamine ligands derived from (+)-camphoric acid were prepared from the reaction of 1,3-diamino-1,2,2-trimethylcyclopentane with aromatic aldehydes, followed by reduction of the corresponding diimines. These newly synthesized ligands were tested in the enantioselective alkylation of benzaldehyde with diethylzinc, giving 1-phenyl-1-propanol with enantiomeric ratios of up to 86:14. Our most selective ligand, derived from 2-methoxybenzaldehyde, was also tested in the alkylation of several aromatic aldehydes and product alcohols with enantiomeric ratios of up to 93.5:6.5 being observed in 2h at room temperature in the presence of 5mol% ligand. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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Cumulative author index ()
Publication date: 15 February 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 2
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Editorial board ()
Publication date: 15 January 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 1
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