- Investigation of Electrostatic Interactions towards Controlling Silylation-Based Kinetic Resolutions
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Electrostatic interactions between a silylated isothiourea intermediate and an ester π system were explored by determining how variations in sterics and electronics affect the selectivity of a silylation-based kinetic resolution. Sterics on the π systems affect the selectivity factors of alkyl 2-hydroxycyclohexanecarboxylates, resulting in a strong correlation of selectivity factors to Charton values. Induction effects of electron-withdrawing substituents on phenyl esters significantly enhance selectivity supporting an edge to face π–π interaction. The linear free energy relationships that were uncovered will aid in future incorporation of intermolecular electrostatic interactions towards controlling asymmetric reactions.
- Zhang, Tian,Redden, Brandon K.,Wiskur, Sheryl L.
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supporting information
p. 4827 - 4831
(2019/08/12)
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- Copper-catalyzed, stereoconvergent,: Cis -diastereoselective borylative cyclization of ω -mesylate- α, β -unsaturated esters and ketones
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The Cu(i)-catalyzed stereoconvergent borylative cyclization of ω-mesylate-α,β-unsaturated compounds is facilitated by a simple Cu-bisphosphine catalyst. This reaction provides a novel route to cis-β-boron-substituted five- and six-membered carbocycle and heterocycle esters. Mechanistic studies indicate that stereoconvergence and cis-substitution likely stem from the rapid enolation of the borylcopper adduct with the substrate double bond and the formation of a five-membered intermediate, respectively.
- Zuo, Ya-Jie,Chang, Xiao-Tong,Hao, Zhi-Ming,Zhong, Chong-Min
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p. 6323 - 6327
(2017/08/10)
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- Candida antarctica lipase B-catalyzed reactions of β-hydroxy esters: Competition of acylation and hydrolysis
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The ester function of ethyl cis-(±)-2-hydroxycyclopentane-1- carboxylate [(±)-1] and ethyl (±)-5-hydroxycyclopent-1- enecarboxylate [(±)-2] was demonstrated to undergo hydrolysis, as a side-reaction, during asymmetric (E > 200) O-acylation with Candida antarctica lipase B (CAL-B) as catalyst and vinyl acetate as acyl donor in t-BuOMe at 30 C. This competition of acylation and undesirable hydrolysis draws attention to CAL-B-catalyzed non-hydrolytic resolutions where the substrates contain any hydrolysable functions. Enantiomerically enriched cis-2-hydroxycyclopentane-1-carboxylic acid (ee = 90%) and 5-hydroxycyclopent-1- enecarboxylic acid (ee = 47%) were prepared through de novo CAL-B-catalyzed hydrolysis of (±)-1 and (±)-2 with added H2O in t-BuOMe at 30 C.
- Forro, Eniko,Galla, Zsolt,Fueloep, Ferenc
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- Modular synthesis of the ClickFerrophos ligand family and their use in rhodium- and ruthenium-catalyzed asymmetric hydrogenation
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A series of diphosphine ClickFerrophos ligands (CF), based on a triazoleferrocene backbone, was synthesized in a four-step sequence via click chemistry methodology. In addition to the four previously synthesized ligands CF1, CF4, CF7 and CF10, six novel C
- Oki, Hiroshi,Oura, Ichiro,Nakamura, Tatsuhito,Ogata, Kenichi,Fukuzawa, Shin-ichi
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experimental part
p. 2185 - 2191
(2010/03/03)
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- Chiral Diphosphonites as Ligands in the Ruthenium-Catalyzed Enantioselective Reduction of Ketones, B-Ketoesters and Ketimines
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Chiral ruthenium complexes are disclosed, obtained by reaction of a ruthenium salt with a chiral diphosphonite. Chiral diols with the general structure given in scheme 1 are preferably used as chiral diphosphonites. Said ruthenium complexes can be simply and economically obtained and provide high enantioselectivity on reduction of ketones, β-ketoesters and ketimines.
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Page/Page column 8-9
(2008/12/04)
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- ClickFerrophos: New chiral ferrocenyl phosphine ligands synthesized by click chemistry and the use of their metal complexes as catalysts for asymmetric hydrogenation and allylic substitution
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The new ferrocenyl P,P- and P,N-ligands 5 and 6 (collectively, "ClickFerrophos") were readily prepared in four steps using Click Chemistry methodology, starting from the commercially available aminoferrocene 1. Rhodium and ruthenium complexes of ClickFerrophos 5 were effective catalysts for the hydrogenation of alkenes and ketones, respectively, producing products with up to 99.7% ee. The analogous palladium complex with 6 worked well for asymmetric allylic alkylation.
- Fukuzawa, Shin-Ichi,Oki, Hiroshi,Hosaka, Mitsuteru,Sugasawa, Jun,Kikuchi, Satoshi
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p. 5557 - 5560
(2008/09/17)
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- Asymmetric hydrogenation of β-keto esters using chiral diphosphonites
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The BINOL-derived diphosphonite having an achiral backbone based on diphenyl ether is a readily accessible and cheap ligand for the enantioselective Ru-catalyzed hydrogenation of β-keto esters (ee = 95-99%).
- Reetz, Manfred T.,Li, Xiaoguang
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p. 1157 - 1160
(2007/10/03)
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- A recombinant ketoreductase tool-box. Assessing the substrate selectivity and stereoselectivity toward the reduction of β-ketoesters
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The substrate selectivity and stereoselectivity of a series of ketoreductases were evaluated toward the reduction of two sets of β-ketoesters. Both the structural variety at β-position and the substituent at α-position greatly affected the activity and stereoselectivity of these ketoreductases. For the first set of β-ketoesters, at least one ketoreductase was found that catalyzed the formation of either (d) or (l) enantiomer of β-hydroxyesters from each substrate with high optical purity, with the only exception of ethyl (d)-3-hydroxy-3-phenylpropionate. For the second set of β-ketoesters with α-substituents, the situation is more complex. More commonly, a ketoreductase was found that formed one of the four diastereomers in optically pure form, with only a few cases in which enzymes could be found that formed two or more of the diastereomers in high optical purity. The continued development of new, more diverse ketoreductases will create the capability to produce a wider range of single diastereomers of 2-substituted-3-hydroxy acids and their derivatives.
- Zhu, Dunming,Mukherjee, Chandrani,Rozzell, J. David,Kambourakis, Spiros,Hua, Ling
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p. 901 - 905
(2007/10/03)
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- Is the ring conformation the most critical parameter in lipase-catalysed acylation of cycloalkanols?
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CAL-B catalysed the resolution of several five and six-membered cyclic β-hydroxy esters efficiently with the exception of the cis-cyclohexanol (±)-4. When employing molecular modelling techniques the conformation turned out to be the most important determ
- Levy, Laura M.,Lavandera, Ivan,Gotor, Vicente
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p. 2572 - 2577
(2007/10/03)
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- New efficient synthesis of Taniaphos ligands: Application in ruthenium- and rhodium-catalyzed enantioselective hydrogenations
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A third generation of Taniaphos 1,5-diphosphine ferrocene ligands with the new and interesting (SFc,3S)- and (RFc,3R)-configurations has been prepared. With these ligands, the ruthenium-catalyzed hydrogenation of C=O bonds proceeded with high diastereo- and enantioselectivity (up to >99% de and 97% ee). Good results were also obtained for the rhodium-catalyzed hydrogenation of C=C (up to 96% ee) and C=N bonds (up to 65% ee).
- Tappe, Katja,Knochel, Paul
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- Lipase-catalysed resolution of cyclic cis- and trans-β-hydroxy esters
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Lipases A and B from Candida antarctica are shown to be highly efficient and complementary biocatalysts for the resolution of five- to seven-membered cyclic β-hydroxy esters by O-acylation. Using this procedure, all four stereoisomers of each one are obtained in enantiopure form and very high yields.
- Levy, Laura M.,Dehli, Juan R.,Gotor, Vicente
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p. 2053 - 2058
(2007/10/03)
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- Synthesis of a new class of chiral 1,5-diphosphanylferrocene ligands and their use in enantioselective hydrogenation
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A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position α to the ferrocene moiety. In many cases, both enantiomeric β-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group.
- Ireland, Tania,Tappe, Katja,Grossheimann, Gabi,Knochel, Paul
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p. 843 - 852
(2007/10/03)
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- 3,3'-bis(diphenylphosphino)-1,1'-disubstituted-2,2'-biindoles: Easily accessible, electron-rich, chiral diphosphine ligands for homogeneous enantioselective hydrogenation of oxoesters
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Racemic (±)-3,3'-bis(diphenylphosphinyl)-1,1'-dimethyl-2,2'-biindole (1c) (N-Me-2-BINPO) and (±)-3,3'-bis(diphenylphosphinyl)-1,1'-bis(methoxymethyl)-2,2'-biindole (1d) (N-MOM-2-BINPO) were synthesized in satisfactory yields following a three-step reaction sequence, starting from indole. Resolution of racemic 1c and 1d was achieved through fractional crystallization of their diastereomeric adducts with optically active dibenzoyl tartaric acids, followed by alkaline decomplexation of the diastereomerically pure salts. Their trichlorosilane reduction gave enantiopure phosphines (+)- and (-)-(1a) (N-Me-2-BINP) and (+)- and (-)-(1b) (N-MOM-2-BINP). The electrochemical oxidative potential of 1a and 1b was found to be 0.52 and 0.60 V, respectively. Both the enantiomers of (1a) were tested as ligands of Ru(II) in asymmetric hydrogenation reactions of α- and β-oxoesters. Reactions were found to be outstandingly fast and enantioselection quite good. Comparative kinetic experiments on the hydrogenation reaction of methyl acetoacetate carried out with 1a, 1c, BINAP, and other biheteroaromatic diphosphines as ligands of Ru(II) demonstrated that all the reactions follow a first-order kinetic. A linear relationship was found between the kinetic constant log and the electrochemical oxidative potential of the diphosphine ligand.
- Benincori,Piccolo,Rizzo,Sannicolo
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p. 8340 - 8347
(2007/10/03)
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- Rhodium-catalyzed reformatsky-type reaction
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(equation presented) A novel Reformatsky-type reaction was developed using RhCl(PPh3)3 and diethylzinc. Inter- and intramolecular Reformatsky-type reactions were achieved efficiently under mild reaction conditions to give β-hydroxy esters.
- Kanai, Kazuo,Wakabayashi, Hitoshi,Honda, Toshio
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p. 2549 - 2551
(2007/10/03)
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- Enantioselective ruthenium-mediated hydrogenation: Developments and applications
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A general preparation of chiral ruthenium(II) catalysts and the homogeneous enantioselective hydrogenation of prochiral olefins and keto groups are presented. Some applications to the synthesis of biologically active compounds are reported.
- Ratovelomanana-Vidal, Virginie,Genet, Jean-Pierre
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p. 163 - 171
(2007/10/03)
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- A chemoenzymatic preparation of both enantiomers of ω-hydroxymethyl-substituted lactones
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(R)- and (S)-δ-hydroxymethyl valerolactone and ε-hydroxymethyl caprolactone were prepared as tert-butyldiphenylsilyl derivatives, in good yield and high enantiomeric purities, in a 5 step sequence, starting from the microbial stereospecific reduction of ethyl 2-oxocyclopentane or 2-oxocyclohexane carboxylates respectively.
- Buisson, Didier,Azerad, Robert
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- A Formal Synthesis of Ptaquilosin. The Aglycon of a Potent Bracken Carcinogen Ptaquiloside
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A formal synthesis of racemic and optically active ptaquilosin has been achieved from the commercially available methyl 2-oxocyclopentanecarboxylate.
- Cossy, Janine,Ibhi, Said,Kahn, Philippe H.,Tacchini, Laura
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p. 7877 - 7880
(2007/10/02)
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- Stereoselective Reduction of Thiocarbonyl Compounds with Baker's Yeast
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Alkyl esters of 3-thioxo-butanoic, -pentanoic and -hexanoic acid, 2-thioxo-1-cyclopentanecarboxylic acid ethyl ester, and 2-octanethione have been reduced with baker's yeast to give optically active thiols.The reductions parallel those of the oxygen analogues with respect to rate and diastereo- and enantioselectivity but, generally, the enantiomeric excess (ee) values are smaller.The influence of experimental variables such as substrate concentration, physiological condition of the yeast (resting/fermenting, fresh/dry/frozen), substrate modification, and addition of inhibitors on stereoselectivity has been studied.The formation of S-products was favoured by small substrate concentrations, use of dry or frozen yeast, and by addition of R-enzyme inhibitors (ethyl acrylate and biacetyl).The yields of thiol products are limited by extensive hydrolysis of the thioxo groups of all substrates used.In order to make meaningful comparisons of enantiomeric preferences in baker's yeast reduction of different substrates it is suggested that the maximum ee values reached below certain (substrate dependent) substrate/yeast ratios are used.
- Nielsen, Jens Kaergaard,Madsen, Joergen Oegaard
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p. 403 - 410
(2007/10/02)
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- Dynamic kinetic resolution of cyclic β-ketoesters with preformed or prepared in situ chiral diphosphine-ruthenium (II) catalysts
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The reduction of racemic β-keto esters having the tetralone structure by chiral ruthenium(II) catalysts is realized with an ideal kinetic dynamic resolution. Remarkably, high anti selectivity approaching 100% and enantioselectivity (up to 97%) using atrop
- Genet,Pfister,Ratovelomanana-Vidal,Pinel,Laffitte
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p. 4559 - 4562
(2007/10/02)
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- Optically active compounds, liquid crystal compositions comprising said compounds and liquid crystal optical modulators using said compositions
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The invention relates to optically active compounds represented by the general formula STR1 wherein R1, R2, Q1, Q2, Q3, STR2 and M are defined as in the specification, methods and intermediates for th
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- Development of new 6-membered chelating chiral bisphosphine ligands for rhodium-catalyzed asymmetric hydrogenation
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A new chiral 1,3-bisphosphine, (1R,2R)-1-diphenylphosphino-2-(diphenylphosphinomethyl)cyclopentane, which was designed to form the favorable skew conformation of the six-membered chelate with rhodium, was developed. Its rhodium complex was found to be one of the most efficient catalysts known for asymmetric hydrogenation of amino acid precursors. Further improvement of this ligand was also attempted for catalytic asymmetric hydrogenation of prochiral ketones to clarify the enantioselective mechanism.
- Inoguchi,Fujie,Yoshikawa,Achiwa
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p. 2921 - 2926
(2007/10/02)
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- Reduction of acyl enolates of alpha-substituted beta-keto esters by bakers' yeast.
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Enol esters of 2-substituted-3-oxoalkanoates of (Z)-configuration were reduced by bakers' yeast to chiral 2-substituted-3-hydroxyalkanoates. The syn-selectivities of this reaction increased compared with those of the reduction of the corresponding racemic
- Ohta,Kobayashi,Sugai
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p. 489 - 493
(2007/10/02)
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- Asymmetric Syntheses of (-)-Malyngolide and (-)-Frontalin by Utilizing Bakers' Yeast Reduction of S-Ethyl 2-Cyclopentanonecarboxylthioate
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Bakers' yeast reduction of S-ethyl 2-cyclopentanonecarboxylthioate affords optically pure S-ethyl (1R,2S)-2-hydroxycyclopentanecarboxylthioate which is stereoselectively converted into (-)-malyngolide and (-)-frontalin.
- Sato, Toshio,Maeno, Hajime,Noro, Tomohiro,Fujisawa, Tamotsu
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p. 1739 - 1742
(2007/10/02)
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- DIASTEREOSELECTIVE AND ENANTIOSELECTIVE MICROBIAL REDUCTION OF CYCLIC alpha-ALKYL beta-KETOESTERS
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The reduction of racemic cyclopenta- and cyclohaxanone 2-carboxyesters by various yeast and mould strains was shown to produce different amounts of isomeric beta-hydroxyesters with predominant (1S) stereochemistry.With several strains, only one optically
- Buisson, Didier,Azerad, Robert
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p. 2631 - 2634
(2007/10/02)
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