- Aromatic cation activation: Nucleophilic substitution of alcohols and carboxylic acids
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A new method for the nucleophilic substitution of alcohols and carboxylic acids using aromatic tropylium cation activation has been developed. This article reports the use of chloro tropylium chloride for the rapid generation of alkyl halides and acyl chlorides under very mild reaction conditions. It demonstrates, for the first time, the synthetic potential of tropylium cations in promoting chemical transformations.
- Nguyen, Thanh V.,Bekensir, Alp
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supporting information
p. 1720 - 1723
(2014/04/17)
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- Catalytic asymmetric α-chlorination of 3-acyloxazolidin-2-one with a trinary catalytic system
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Direct asymmetric α-chlorination of aryl acetic acid derivatives was achieved with a novel trinary activation system consisting of a catalytic amount of NiCl2/(R)-BINAP, Et3SiOTf, and a tertiary amine base. The reaction smoothly affo
- Hamashima, Yoshitaka,Nagi, Tatsuya,Shimizu, Ryo,Tsuchimoto, Teruhisa,Sodeoka, Mikiko
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scheme or table
p. 3675 - 3678
(2011/09/15)
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- Nitrile hydratase activity of a recombinant nitrilase
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Appreciable amounts of amide are formed in the course of nitrile hydrolysis in the presence of recombinant nitrilase from Pseudomonas fluorescens EBC 191, depending on the α-substituent and the reaction conditions. The ratio of the nitrilase and nitrile hydratase activities of the enzyme is profoundly influenced by the electronic and steric properties of the reactant. In general, amide formation increased when the α-substituent was electron-deficient; 2-chloro-2-phenylacetonitrile, for example, afforded 89% amide. We found, moreover, that (R)-mandelo-nitrile was hydrolysed with 11% of amide formation whereas 55% amide was formed from the (S)-enantiomer; a similar effect was found for the O-acetyl derivatives. A mechanism that accomodates our results is proposed.
- Fernandes, Bruno C. M.,Mateo, Cesar,Kiziak, Christoph,Chmura, Andrzej,Wacker, Jan,Van Rantwijk, Fred,Stolz, Andreas,Sheldon, Roger A.
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p. 2597 - 2603
(2007/10/03)
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- Enzymatic hydrolysis and selective racemisation reactions of α-chloro esters
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The kinetic resolution of α-chloro esters was effected with good selectivity using CLEC (Cross-Linked Enzyme Crystals) enzymes. The selective racemisation of α-chloro esters in the presence of α-chloro acids enabled a successful dynamic kinetic resolution reaction to be performed.
- Haughton, Louise,Williams, Jonathan M. J.
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p. 943 - 946
(2007/10/03)
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- Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Bronsted acids: Reaction scope and mechanistic insights
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Enantioselective protonation is a potent and efficient way to construct chiral carbons. Here we report details of the reaction using Lewis acid-assisted chiral Bronsted acids (chiral LBAs). The 1:1 coordinate complex of tin tetrachloride and optically active binaphthol ((R)- or (S)-BINOL) can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α-aryl ketones and α-arylcarboxylic acids, respectively, with high enantiomeric excesses (up to 98% ee). A catalytic version of enantioselective protonation has also been achieved using stoichiometric amounts of 2,6-dimethylphenol and catalytic amounts of monomethyl ether of optically active BINOL in the presence of tin tetrachloride. This protonation is also effective for producing α-halocarbonyl compounds (up to 91% ee). DFT calculations on the B3LYP/LANL2DZ level show that the conformational structure of the chiral LBA and the orientation of activated proton on (R)-BINOLs are important for understanding the absolute stereochemistry of the products.
- Nakamura, Shingo,Kaneeda, Masanobu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 8120 - 8130
(2007/10/03)
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- Enantioselective Protonation of Ketene Bis(trimethylsilyl) Acetals Derived from α-Aryl-α-haloacetic Acids Using LBA
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Optically active α-halocarboxylic acids and derivatives are important and versatile building blocks in organic synthesis. Lewis acid assisted chiral Bronsted acid (LBA) was recently prepared in situ from tin(IV) tetrachloride and optically pure binaphthol
- Ishihara, Kazuaki,Nakamura, Shingo,Yamamoto, Hisashi
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p. 513 - 517
(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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