- Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters
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A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.
- Greenhalgh, Mark D.,Laina-Martín, Víctor,Neyyappadath, Rifahath M.,Qu, Shen,Smith, Andrew D.,Smith, Samuel M.
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p. 16572 - 16578
(2020/09/09)
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- Highly efficient C-H hydroxylation of carbonyl compounds with oxygen under mild conditions
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A transition-metal-free Cs2CO3-catalyzed α-hydroxylation of carbonyl compounds with O2 as the oxygen source is described. This reaction provides an efficient approach to tertiary α-hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp3)-H bond cleavage. OH, so simple! A transition-metal-free Cs2CO 3-catalyzed α-hydroxylation of carbonyl compounds with O 2 provided a variety of tertiary α-hydroxycarbonyl compounds (see scheme; DMSO=dimethyl sulfoxide), which are widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very efficient and practical.
- Liang, Yu-Feng,Jiao, Ning
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p. 548 - 552
(2014/01/23)
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- Highly homogeneous stereocontrolled construction of quaternary hydroxyesters by addition of dimethylzinc to α-ketoesters promoted by chiral perhydrobenzoxazines and B(OEt)3
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A highly efficient enantioselective addition of Me2Zn to α-ketoesters, assisted by a chiral perhydro-1,3-benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α-hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α-ketoesters are employed. The catalyst can be recovered and reused without loss of activity.
- Infante, Rebeca,Nieto, Javier,Andres, Celia
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supporting information; experimental part
p. 4375 - 4379
(2012/05/20)
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- Enantioselective synthesis of quaternary stereogenic centers through catalytic asymmetric addition of dimethylzinc to α-ketoesters with chiral cis-cyclopropane-based amide alcohol as ligand
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A new amino alcohol with a chiral cyclopropane backbone has been developed and used in the catalytic asymmetric diethylzinc addition to various types of α-ketoesters. This cyclopropane-based chiral amino alcohol shows moderate enantioselectivity in the ad
- Zheng, Bing,Hou, Shicong,Li, Zhiyuan,Guo, Hongchao,Zhong, Jiangchun,Wang, Min
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experimental part
p. 2125 - 2129
(2010/03/01)
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- Enantioselective addition of dimethylzinc to α-keto esters
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The readily available (+)-N-Benzyl-(S)-mandelamide catalyzes the enantioselective addition of dimethylzinc to α-keto esters to give α-methyl-α-hydroxy esters containing stereogenic quaternary centers with moderate to good yields (56-87%). A good enantioselectivity of the reaction is obtained for aryl and heteroaryl keto esters. For these substrates ee values of 75-90% are obtained. The enantioselectivity is somewhat lower for the substrates bearing an aliphatic chain. Georg Thieme Verlag Stuttgart.
- Blay, Gonzalo,Fernandez, Isabel,Marco-Aleixandre, Alicia,Pedro, Jose R.
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p. 3754 - 3757
(2008/09/19)
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- Anionic four-electron donor-based palladacycles as catalysts for addition reactions of arylboronic acids with α,β-unsaturated ketones, aldehydes, and α-ketoesters
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(Chemical Equation Presented) Anionic four-electron donor-based palladacycle-catalyzed 1,4-additions of arylboronic acids with α,β-unsaturated ketones and 1,2-additions of arylboronic acids with aldehydes and α-ketoesters are described. Our study demonstrated that palladacycles were highly efficient, practical catalysts for these addition reactions. The work described here not only opened a new paradigm for the application of palladacycles, but may also pave the road for other metalacycles as practically useful catalysts for such addition reactions including asymmetric ones.
- He, Ping,Lu, Yong,Dong, Cheng-Guo,Hu, Qiao-Sheng
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p. 343 - 346
(2007/10/03)
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- Rhodium-catalyzed addition of aryl boronic acids to 1,2-diketones and 1,2-ketoesters
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The metal complex Rh(acac)(CO)2 in the presence of dicyclohexylphenylphosphine provides a useful catalyst system for the addition of boronic acids to 1,2-diketones and 1,2-ketoesters. The best yields were obtained when the transformation was pe
- Ganci, Gregory R.,Chisholm, John D.
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p. 8266 - 8269
(2008/03/14)
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- Catalytic asymmetric addition of dimethylzinc to α-ketoesters, using mandelamides as ligands
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A strategy based on the control of the electron-donating capabilities of the coordinating groups of the ligand has been applied in the catalytic asymmetric addition of organometallic reagents to ketoesters. Mandelamides having deprotonated alcohol and carboxyamido groups catalyzed the addition of dimethylzinc to α-ketoesters with good yields and ee (up to 90%).
- Blay, Gonzalo,Fernandez, Isabel,Marco-Aleixandre, Alicia,Pedro, Jose R.
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p. 1287 - 1290
(2007/10/03)
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- Multicenter Strategy for the Development of Catalytic Enantioselective Nucleophilic Alkylation of Ketones: Me2Zn Addition to α-Ketoesters
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An array of heteroatoms is essential for the activity and enantioselectivity of the catalyst 2 in the addition of Me2Zn to α-ketoesters 1 (e.g. see equation). α-Hydroxyesters 3 were obtained with up to 96% ee in the presence of a catalytic amount of additive iPrOH, which serves to generate the catalytically active monomeric species (based on the observation of nonlinear effects).
- Funabashi, Ken,Jachmann, Markus,Kanai, Motomu,Shibasaki, Masakatsu
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p. 5489 - 5492
(2007/10/03)
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- Rhodium-catalyzed addition of arylstannanes to carbon-heteroatom double bond
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The addition of arylstannanes to the carbon-heteroatom double bond in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) was examined. The reactions of aldehydes, α-dicarbonyl compounds, and N-substituted aldimines with the arylstannanes gave corresponding alcohols, α-hydroxy carbonyl compounds, and amines, respectively. An arylrhodium complex generated by the transmetalation with the arylstannane was probably the active catalytic species.
- Oi, Shuichi,Moro, Mitsutoshi,Fukuhara, Hiroe,Kawanishi, Takanori,Inoue, Yoshio
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p. 4351 - 4361
(2007/10/03)
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- Copper(II) chloride dihydrate: A catalytic agent for the deprotection of tetrahydropyranyl ethers (THP ethers) and 1-ethoxyethyl ethers (EE ethers)
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Tetrahydropyranyl ethers (THP groups) and 1-ethoxyethyl ethers (EE groups) are removed upon refluxing in 95% EtOH or Me2CO-H2O (95:5) in the presence of a catalytic amount of copper(II) chloride dihydrate (2-5 mol%).
- Wang, Jianbo,Zhang, Chao,Qu, Zhaohui,Hou, Yihua,Chen, Bei,Wu, Peng
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p. 294 - 295
(2007/10/03)
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- Ethyl Mandelate as a Convenient New Benzoyl Anion Equivalent
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Ethyl mandelate acts as a convenient benzoyl anion equivalent for the formation of alkyl aryl ketones by deprotonation-alkylation followed by flash vacuum pyrolysis.
- Aitken, R. Alan,Thomas, Andrew W.
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p. 293 - 294
(2007/10/03)
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- α-Fluoro analogues of inflammation inhibiting α-arylpropionic acids
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2-Aryl-2-fluoropropionic acids were prepared by treatment of either ethyl α-hydroxy-carboxylates or cyanohydrin O-silyl ethers with diethylaminosulfur trifluoride and subsequent hydrolysis. The methyl ester of 2-fluoro-2-(4- isobutylphenyl)propionic acid
- Schlosser, Manfred,Michel, Dominique,Guo, Zhi-Wei,Sih, Charles J.
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p. 8257 - 8262
(2007/10/03)
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- Effect of fluorine substitution of α-and β-hydrogen atoms in ethyl phenylacetate and phenylpropionate on their stereoselective hydrolysis by cultured cancer cells
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(±)-Ethyl 2-fluoro-2-phenylacetate was stereoselectively hydrolyzed by cultured cells of several rat cancer cell lines to give the carboxylic acid rich in the R enantiomer. The stereoselectivity increased for (±)-ethyl 2-fluoro-2-phenylpropionate (2b) with all present cell lines and for (±)-ethyl 2-phenyl-3,3,3-trifluoropropionate (3b) with rat hepatoma McA-RH7777 cell line. The stereoselectivity was different for the different cell lines, as McA-RH7777 cells preferred (R)-2b in contrast with the preference towards (S)-2b by other cells such as ras oncogene-transformed rat liver Anr4 cells. These stereoselectivities were different from those for non-fluorinated (±)-ethyl 2-phenylpropionate. Thus fluorine atoms are recognized by ester hydrolases of cancer cells, and fluorine substitution on the acyl group will be useful for making ester-type anticancer prodrugs more specific to cancer cells.
- Yamazaki, Yoshimitsu,Yusa, Shiro,Kageyama, Yu-Ichi,Tsue, Hirohito,Hirao, Ken-Ichi,Okuno, Hiroaki
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p. 167 - 171
(2007/10/03)
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- Heteroacetic acid derivatives
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Disclosed are compounds of formula STR1 wherein R is hydroxy, esterified hydroxy or etherified hydroxy; R1 is halogen, trifluoromethyl or lower alkyl; R2 is halogen, trifluoromethyl or lower alkyl; R3 is halogen, trifluoromethyl, lower alkyl, aryl, aryl-lower alkyl, cycloalkyl or cycloalkyl-lower alkyl; or R3 is the radical STR2 wherein R8 is hydrogen, lower alkyl, aryl, cycloalkyl, aryl-lower alkyl or cycloalkyl-lower alkyl; R9 is hydroxy or acyloxy; R10 represents hydrogen or lower alkyl; or R9 and R10 together represent oxo; R4 is hydrogen, halogen, trifluoromethyl or lower alkyl; X is --NR7, S or O; W is O or S; R5 represents hydrogen, lower alkyl or aryl-lower alkyl;and R6 represents hydrogen; or R5 and R6 together represent oxo provided that X represents --NR7; R7 represents hydrogen or lower alkyl; Z represents carboxyl, carboxyl derivatized as a pharmaceutically acceptable ester or as a pharmaceutically acceptable amide; and pharmaceutically acceptable salts thereof; which are useful as hypocholesteremic agents.
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