- 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)
-
- Chemoenzymatic approaches to the synthesis of the (1S,2R)-isomer of benzyl 2-hydroxycyclohexanecarboxylate
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We examined ten strains of cultured whole-cell yeasts for the asymmetric reduction of commercially available ethyl 2-oxocyclohexanecarboxylate, and found that the (1S,2S)-stereoisomer of ethyl 2-hydroxycyclohexanecarboxylate was the major stereoisomer produced by Williopsis californica JCM 3600. The ethyl group of the ester was then substituted with a benzyl group with low volatility and increased hydrophobicity to facilitate the isolation of the expected product. Incubation with W. californica furnished benzyl (1S,2S)-2-hydroxycyclohexanecarboxylate (>99.9% ee) in 51.0% yield together with its (1R,2S)-isomer (>99.9% ee) in 35.4% yield. Upon treatment of the same substrate bearing the benzyl ester with a screening kit of purified overexpressed carbonyl reductases (Daicel Chiralscreen OH), two enzymes (E031, E078) furnished the (1R,2S)-isomer as the major product. With another enzyme (E007), the (1S,2R)-isomer was obtained, but its ee was very low (25.6%). The highly enantiomerically enriched (1S,2S)-isomer obtained by W. californica was transformed to the (1S,2R)-isomer (>99.9% ee), whose availability until now has been low, in 43.3% yield over two steps involving tosylation and subsequent inversive attack with tetrabutylammonium nitrite.
- Tsunekawa, Ryuji,Hanaya, Kengo,Higashibayashi, Shuhei,Shoji, Mitsuru,Sugai, Takeshi
-
-
- BIARYL PYRAZOLES AS NRF2 REGULATORS
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The present invention relates to biaryl pyrazole compounds, methods of making them, pharmaceutical compositions containing them and their use as NRF2 regulators.
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-
Page/Page column 455
(2017/08/01)
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- New Route to Stabilize Ruthenium Nanoparticles with Non-Isolable Chiral N-Heterocyclic Carbenes
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Ru nanoparticles (RuNPs) stabilized by non-isolable chiral N-heterocyclic carbenes (NHCs), namely SIDPhNp ((4S,5S)-1,3-di(naphthalen-1-yl)-4,5-diphenylimidazolidine) and SIPhOH ((S)-3-((1S,2R)-2-hydroxy-1,2-diphenylethyl)-1-((R)-2-hydroxy-1,2-diphenylethyl)-4,5-dihydro-3H-imidazoline), have been synthesized through a new procedure that does not require isolation of the free carbenes. The obtained RuNPs have been characterized by state-of-the-art techniques and their surface chemistry has been investigated by FTIR and solid-state MAS NMR upon the coordination of CO, which indicated the presence of free and reactive Ru sites. Their catalytic activity has been tested in various hydrogenation reactions involving competition between different sites, whereby interesting differences in selectivity were observed, but no enantioselectivity.
- Martnez-Prieto, Luis Miguel,Ferry, Anglique,Lara, Patricia,Richter, Christian,Philippot, Karine,Glorius, Frank,Chaudret, Bruno
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p. 17495 - 17502
(2016/01/25)
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- Enantioselective ketoester reductions in water: A comparison between microorganism-and ruthenium-catalyzed reactions
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In the search for green chemistry methods for the enantioselective reduction of ketoesters Saccharomyces cerevisiae-and ruthenium-catalyzed reactions in water have been investigated. The highest enantiomeric excesses for the reduction of α-and β-ketoesters have been obtained by S. cerevisiae. Chiral ruthenium catalysts are active for the reduction of all ketoesters with low to moderate enantioselectivities depending on the nature of the substrate and ligand. Interestingly, for several substrates both enantiomers of the hydroxyesters have been obtained according either to the catalytic method or to the structure of the ligand.
- Zeror, Saoussen,Collin, Jacqueline,Fiaud, Jean-Claude,Zouioueche, Louisa Aribi
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experimental part
p. 1211 - 1215
(2010/10/20)
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- Synthesis and characterization of the enantiomerically pure cis- and trans-2,4-dioxa-3-fluoro-3-phosphadecalins as inhibitors of acetylcholinesterase
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The title compounds, the P(3)-axially- and P(3)-equatorially-substituted cis- and trans-configured 3-fluoro-2,4-dioxa-3-phosphadecalin 3-oxides (= 3-fluoro-2,4-dioxa-3-phosphabicyclo[4.4.0]decane 3-oxides) have been prepared (ee > 99%) and fully character
- Waechter, Michael,Rueedi, Peter
-
experimental part
p. 283 - 294
(2010/04/23)
-
- Effects of methyl substituents on the activity and enantioselectivity of homobenzotetramisole-based catalysts in the kinetic resolution of alcohols
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Substitution of the tetrahydropyrimidine ring in the enantioselective acyl transfer catalyst homobenzotetramisole (HBTM) 6 with methyl groups exerts a dramatic influence on its performance in the kinetic resolution of secondary alcohols. The syn-3-methyl analogue of HBTM (9a) has proved to be superior to the parent compound in terms of catalytic activity, enantioselectivity, and synthetic accessibility.
- Zhang, Yuhua,Birman, Vladimir B.
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supporting information; scheme or table
p. 2525 - 2529
(2009/12/28)
-
- Homobenzotetramisole: An effective catalyst for kinetic resolution of aryl-cycloalkanols
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Homobenzotetramisole (HBTM), a ring-expanded analogue of the previously reported catalyst BTM, displays higher catalytic activity and a different structure-selectivity profile. It displays good enantioselectivities in kinetic resolution of secondary benzylic alcohols but is particularly effective for 2-aryl-substituted cycloalkanols.
- Birman, Vladimir B.,Li, Ximin
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supporting information; experimental part
p. 1115 - 1118
(2009/04/07)
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- Carbonylative ring opening of terminal epoxides at atmospheric pressure
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(Chemical Equation Presented) The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2-(CO) 8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.
- Denmark, Scott E.,Ahmad, Moballigh
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p. 9630 - 9634
(2008/03/17)
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- Reductions of cyclic β-keto esters by individual Saccharomyces cerevisiae dehydrogenases and a chemo-enzymatic route to (1R,2S)-2-methyl-1-cyclohexanol
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Twenty purified dehydrogenases cloned from bakers' yeast (Saccharomyces cerevisiae) and expressed as fusion proteins with glutathione (S)-transferase were tested for their ability to reduce three homologous cyclic β-keto esters. The majority of dehydrogenases reduced ethyl 2-oxo-cyclopentanecarboxylate, yielding a pair of diastereomeric alcohols with consistent (1R)-stereochemistry. Ethyl 2-oxo-cyclohexanecarboxylate reductions afforded only cis-alcohol enantiomers. Ethyl 2-oxo-cycloheptanecarboxylate was accepted by two enzymes in the collection, and both yielded mainly the cis-(1R,2S)-alcohol. Escherichia coli cells overexpressing the YDL124w gene were used in a dynamic kinetic resolution of ethyl 2-oxo-cyclohexanecarboxylate to produce the key intermediate in a chemo-enzymatic synthesis of (1R,2S)-2-methyl-1-cyclohexanol, an important chiral building block.
- Padhi, Santosh Kumar,Kaluzna, Iwona A.,Buisson, Didier,Azerad, Robert,Stewart, Jon D.
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p. 2133 - 2138
(2008/02/11)
-
- 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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- Method for producing optically active 2-hydroxycycloalkanecarboxylic acid ester
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There is disclosed a method for producing optically active 2-hydroxycycloalkanecarboxylic acid characterized by the steps of: allowing 2-oxocycloalkanecarboxylic acid ester to react with a transformant or a dead cell artificially provided with an ability to asymmetrically reduce 2-oxocycloalkanecarboxylic acid ester to optically active 2-hydroxycycloalkanecarboxylic acid ester and an ability to regenerate a coenzyme on which an enzyme having the former ability depends; and collecting the produced optically active 2-hydroxycycloalkanecarboxylic acid ester.
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-
- Stereoselective bioreduction to a chiral building block on a kilogram scale
-
The highly stereoselective bioreduction of ethyl cyclohexanone-2-carboxylate (1) on a kilogram scale is described. Ethyl(1S,2S)-trans-2-hydroxycyclohexane carboxylate (2) was prepared in 56% yield with a diastereomeric ratio (dr) of 99:1 and an enantiomer
- Jablonski-Lorin, Christelle,Melillo, Vito,Hungerbuehler, Ernst
-
p. 574 - 576
(2007/10/03)
-
- Synthesis of a new class of chiral 1,5-diphosphanylferrocene ligands and their use in enantioselective hydrogenation
-
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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- 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)
-
- Stereoselective synthesis of novel anti-MRSA tricyclic carbapenems (trinems)
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(4S)-Hydroxymethyltrinem 3 was prepared via stereoselective aldol-type reaction with optically pure (R)-2-t-butyldimethylsilyloxymethylcyclohexanone ((R)-16). (4S)-Hydroxymethyltrinem 3 was converted into various kinds of trinem derivatives with anti-MRSA activity by using the Mitsunobu reaction. (C) 2000 Elsevier Science Ltd.
- Kanno, Osamu,Kawamoto, Isao
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p. 5639 - 5648
(2007/10/03)
-
- Catalytic asymmetric acylation of racemic secondary alcohols with benzoyl chloride in the presence of a chiral diamine
-
Nonenzymatic kinetic resolution of racemic secondary alcohols is an efficient synthetic method to obtain optically active compounds in organic chemistry. Catalytic asymmetric acylation of racemic secondary alcohols has been successfully performed with achiral benzoyl chloride in the presence of only 0.3 mol% of chiral diamine (3) derived from (S)-proline, combined with 0.5 equivalent of triethylamine. This asymmetric acylation of various racemic cyclic secondary alcohols, 5, 6, or 8 membered cycloalkanols (1a-1c), hydroxyesters (1d and 1e), and bromohydrins (1f and 1g) gave the corresponding optically active benzoates (84-97% ee) and unreacted alcohols (79-95% ee). Racemic acyclic secondary alcohols (1h-1j) were also acylated in moderate enantioselectivity.
- Sano, Tomohumi,Imai, Keisuke,Ohashi, Kousaburo,Oriyama, Takeshi
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p. 265 - 266
(2007/10/03)
-
- BENZAMIDINE DERIVATIVES SUBSTITUTED BY CYCLIC AMINO ACID AND CYCLIC HYDROXY ACID DERIVATIVES AND THEIR USE AS ANTI-COAGULANTS
-
This invention is directed to benzamidine derivatives substituted by cyclic amino acid and cyclic hydroxy acid derivatives which are useful as anti-coagulants. This invention is also directed to pharmaceutical compositions containing the compounds of the invention, and methods of using the compounds to treat disease-states characterized by thrombotic activity.
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-
- Enantioselective ruthenium-mediated hydrogenation: Developments and applications
-
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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- Highly stereocontrolled synthesis of enantiomeric 4-methoxy trinems via resolution of scalemic enol phosphates
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Stereocontrolled syntheses of 4-methoxy trinem 2 and its enantiomer 3 were achieved using the ester enolate N-trimethylsilylimine approach. The key step was the resolution of racemic enolphosphates derived from ephedrine.
- Panunzio, Mauro,Camerini, Roberto,Pachera, Roberta,Donati, Daniele,Marchioro, Carla,Perboni, Alcide
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p. 2929 - 2938
(2007/10/03)
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- Highly stereocontrolled synthesis of a novel tribactam by reaction of an ester enolate with a N-trimethylsilylimine
-
The azetidinone 14, a key intermediate in the synthesis of novel tribactam antibiotics (e.g. 2) was obtained via condensation of an ester enolate with a N-trimethylsilylimine.
- Camerini, Roberto,Panunzio, Mauro,Bonanomi, Giorgio,Donati, Daniele,Perboni, Alcide
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p. 2467 - 2470
(2007/10/03)
-
- Stereo- and chemoselective transfer hydrogenation of carbonyl groups with RuCl2(PPh3)3 and BINAP-Ru as catalysts and et3NH+H2PO2-·1,5H 2O as a hydrogen donor
-
Using Et3NH+H2PO2-.1.5 H2O as a hydrogen donor, the RuCl2(Ph3P)3, RuCl2(PPh3)3 / C and BINAP-Ru proved highly active catalysts for transfer hydrogenation of ketones under milder conditions than other hydrogen donors. 2-Methyl-, 2-chloro-, 2-(ethoxycarbonyl)cyclohexanones and -cyclopentanones were reduced to the less stable axial alcohols in excellent diastereoisomeric excess (de: 90-100%), and the carbonyl group of α,β-unsaturated ketones was selectively reduced, in contrast with other hydrogen donors the C=C bond was reduced. Copyright
- Khai, Bui The,Arcelli, Antonio
-
p. 6599 - 6602
(2007/10/03)
-
- A chemoenzymatic preparation of both enantiomers of ω-hydroxymethyl-substituted lactones
-
(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
-
-
- Heterocyclic compounds
-
A method of combating undesired plant growth in wheat, comprising treating said undesired plant growth with an effective amount of a compound of the formula I STR1 in which n is an integer from 1 to 6; m is an integer from 0 to 2n+2; X represents an oxyge
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-
- Dynamic kinetic resolution of cyclic β-ketoesters with preformed or prepared in situ chiral diphosphine-ruthenium (II) catalysts
-
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
-
p. 4559 - 4562
(2007/10/02)
-
- Enzymatic Preparation of Optically Active α- and β-Hydroxy Carboxylic Acid Derivatives
-
The lipase PS-catalysed resolutions of mandelonitrile (1) and methyl and ethyl hydroxy carboxylates 2-5 have been performed using (PrCO)2O, PrCO2CH=CH2 and PrCO2CH2CF3 as achiral reagents in THF and toluene.High enantioselectivity (e.e. close to 100percent) was observed, especially when butyric anhydride was used as an acylating reagent for the secondary HO group of 2-5. The acylation using PrCO2CH2CF3 was impractical owing to the slow reaction rate.In the acylation of 1 enentioselectivity was only moderate.
- Kanerva, Liisa T.,Sundholm, Oskari
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p. 823 - 825
(2007/10/02)
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- Stereoelectronic Influence on the NaBH4 Reduction Stereoselectivity of Alicyclic β-ketoesters
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The stereochemistry of β-hydroxyesters produced in the NaBH4 reduction of alicyclic β-ketoesters has been determined.An enhanced rate of reduction has been observed for those isomers in which the carboxylate is antiperiplanar to the hydride ion in the tra
- Beeson, Craig,Pham, Nguyen,Dix, Thomas A.
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p. 2925 - 2928
(2007/10/02)
-
- Studies on the Chemo- and Enantio-selectivity of the Enzymatic Monoacylations of Amino Alcohols
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The formation of ω-aminoalkyl esters through the lipase PS (Pseudomonas cepacia)-catalysed transesterification between carboxylic acid esters 1-6 and ω-amino-1-alkanols in tert-amyl alcohol has been studied.For n = 5 or 6 the reaction practically leads to the formation of the ester product.The ester/amide ratios decrease with decreasing n so that for n = 3 only the amide product is obtained.A moderate kinetic resolution (ca. 50percent e.e. at 50percent conversion) was found in the acylations with two of the racemic starting esters (3 and 4).
- Kanerva, Liisa T.,Kosonen, Markus,Vaenttinen, Eero,Huuhtanen, Tuomas T.,Dahlqvist, Martti
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p. 1101 - 1105
(2007/10/02)
-
- Heterocyclic compounds
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Compounds of formula I wherein nis 1 to 6; mis 0 to 2n+2; X is oxygen, sulphur, sulphinyl or sulphonyl; R1, R2 and R3 are each, independently, hydrogen, halogen, formyl, cyano, carboxy, azido or optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alke
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- Reduction of acyl enolates of alpha-substituted beta-keto esters by bakers' yeast.
-
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
-
p. 489 - 493
(2007/10/02)
-
- Synthesis of β-Hydroxy Esters by Lithium/Ammonia Reduction of α,β-Epoxy Esters
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Aliphatic β-hydroxy esters (alkyl 3-hydroxyalkanoates) are conveniently prepared in high yield by regioselective lithium /ammonia reduction of α,β-epoxy esters (alkyl 2,3-epoxyalkanoates).
- Baan, J. L. van der,Barnick, J. W. F. K.,Bickelhaupt, F.
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p. 897 - 899
(2007/10/02)
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- 65. Homogeneous and Heterogeneous Asymmetric Reactions. Part 5. Diastereoselective and Enantioselective Hydrogenation of Cyclic β-Keto Esters on Modified Raney-Nickel Catalysts
-
The hydrogenations of methyl 2-oxocyclopentanecarboxylate (1), ethyl 2-oxocyclohexanecarboxylate (3), and 2-methylcyclohexanone (5) on unmodified Raney-Ni catalyst lead predominantly to the formation of the cis-hydroxy diastereoisomers of 2, 4, and 6, respectively (Scheme 2).In the asymmetric hydrogenations on catalysts modified with chiral tartaric acid (R,R)-C4H6O6/Raney-Ni and (R,R)-C4H6O6/NaBr/Raney-Ni), the predominance of the cis-isomer increases significantly.The hydrogenations of β-keto esters 1 and 3 proceed with an enantioselectivity of 10-15percent on the modified catalysts, while the similar hydrogenation of 5 yields optically inactive 6.The (1S,2R)-enantiomers of the cis-isomers of 2 and 4 are formed in larger quantity, whereas the (1R,2R)-enantiomers of the corresponding trans-isomers predominate (Scheme 1).The enantioselective formation of trans-2 and trans-4 can be interpreted mainly in terms of the asymmetric hydrogenation of cyclic β-keto esters through the keto form, while that of the corresponding cis-hydroxy esters proceeds through the enol form.
- Wittmann, Gyula,Goendoes, Gyoergy,Bartok, Mihaly
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p. 635 - 639
(2007/10/02)
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- Dynamic Kinetic Resolution in BINAP-Ruthenium(II) Catalyzed Hydrogenation of 2-Substituted 3-Oxo Carboxylic Esters
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BINAP-Ru catalyzed hydrogenation allows efficient dynamic kinetic resolution of certain 2-substituted 3-oxo carboxylic esters having cyclic structures to lead to the alcoholic products in high enantiomeric and diastereomeric excess.
- Kitamura, M.,Ohkuma, T.,Tokunaga, M.,Noyori, R.
-
-
- Pyrimidine derivatives and herbicide containing the same
-
Disclosed are pyrimidine derivatives of the formula (I) and optical isomers thereof and a herbicide containing one or more of them as an active ingredient. STR1 where W is O or S; X is a lower alkyl group or a lower alkoxycarbonyl group; R is H, an option
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- Chiral Alkoxytitanium(IV) Complexes for Enantioselective Nucleophilic Additions to Aldehydes and as Lewis Acids in Diels-Alder Reactions
-
A number of chiral 1,2- 1,3-and 1,4-diols were prepared and used as alkoxy ligands on Ti for enantioselective nucleophilic transfer of methyl, butyl, cyclopropyl, allyl, alkinyl, and phenyl groups to aromatic adehydes, as wellas for the enantioselective cycloaddition of acrylate to cyclopentadiene.The 1,2-diols were pinane diol 7 and 1,2:5,6-diacetonide-protected mannitol 9 (Scheme 3) and tartrates.The 1,3-diols were obtained from the yeast-reduction products of 2-oxocyclopentane- and 2-oxocyclohexanecarboxylates and excess MeLi, BuLi, or PhLi (or the corresponding Grignard reagents; see 4-6).As 1,4-diols, we used the products 2 and 3 from tartrate acetals and methyl or phenyl Grignard reagents, the bis(benzaldehyde)acetal 8 of D-mannitol and o,o'-binaphthol (22).These diols were attached to the Ti-atom by azeotropic removal of i-PrOH from a mixture with .Addition of various organometallic reagents R-metal (metal=Li, BR3, MgX, MnCl, CuLiR) was followed by combination with aldehydes at -75 degC, a warmup period, quenching with aqueous KF solution, and workup (for results see Tables 1-6 and Formulae 17-20).The enantiomeric excess of the secondary alcohols obtained varies greatly, certain combinations of chiral ligands, nucleophilic groups, and aldehyde substrates give rise to values as high as 90 percent ee; see e.g.Table 4.The Ti-complexes of the general formula *O)2Cl2> or *O)2(i-PrO)Cl> induced the Diels-Alder addition of methyl acrylate to cyclopentadiene to take place at - 30 degC.The best enantioselectivity (50percentee) was observed with the binaphthol derivative (Table 7.) The structures of the complexes involved in these reactions are unknown.The substitution on C(2) of the dioxolanes 2 and 3 (derived from tartaric acid) has a pronounced effect on the selectivities of both reactions studied here (Tables 2,3, and 7).This remote effect (1,6-distance between the stereogenic acetal-C-atom and the Ti-centers) must be caused by conformational changes in the vicinity of the reactive site, i.e. the Ti-C bond in the nucleophilic addition reactions and the Ti-acrylate-oxygen complexation in the Diels-Alder reaction.
- Seebach, Dieter,Beck, Albert K.,Imwinkelried, Rene,Roggo, Silvio,Wonnacott, Anne
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p. 954 - 974
(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
-
p. 2631 - 2634
(2007/10/02)
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- 144. Ueber die Stereoselektivitaet der α-Alkylierung von (1R,2S)(+)-cis-2-Hydroxy-cyclohexancarbonsaeureaethylester
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In continuation of our work on the stereoselectivity of the α-alkylation of β-hydroxyesters , we studied this reaction with the title compound (+)-2.The latter was prepared through reduction of 1 with baker's yeast.Alkylation of the dianion of (+)-
- Frater, Gyoergy
-
p. 1383 - 1390
(2007/10/02)
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- The synthetic utility of amine borane reagents in the reduction of aldehydes and ketones
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Primary and secondary amine boranes have been shown to be mild, efficient, and stereoselective reducing agents for aldehydes and ketones in protic or non-protic solvents with reactivity patterns different than diborane or sodium borohydride.
- Andrews,Crawford
-
p. 693 - 696
(2007/10/02)
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