- Catalyst-Controlled Multicomponent Aziridination of Chiral Aldehydes
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A highly diastereoselective and enantioselective method for the multicomponent aziridination of chiral aldehydes has been developed with BOROX catalysts of the VANOL (3,3′-diphenyl-2,2′-bi-1-naphthol) and VAPOL (2,2′-diphenyl-(4-biphenanthrol)) ligands. Very high to perfect catalyst control is observed with most all substrates examined including aldehydes with chiral centers in the α- and β-positions. High catalyst control was also observed for a number of chiral heterocyclic aldehydes allowing for the preparation of epoxy aziridines, bis(aziridines) and ethylene diaziridines. Application of this reaction in the synthesis of β3-homo-d-alloisoleucine and β3-homo-l-isoleucine is reported.
- Mukherjee, Munmun,Zhou, Yubai,Dai, Yijing,Gupta, AniL K.,Pulgam, V. Reddy,Staples, Richard J.,Wulff, William D.
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supporting information
p. 2552 - 2556
(2017/03/06)
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- Bronsted acid catalyzed asymmetric aldol reaction: A complementary approach to enamine catalysis
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A syn-enantioselective aldol reaction has been developed using Bronsted acid catalysis based on H8-BINOL-derived phosphoric acids. This method affords an efficient synthesis of various β-hydroxy ketones, some of which could not be synthesized u
- Pousse, Guillaume,Cavelier, Fabien Le,Humphreys, Luke,Rouden, Jacques,Blanchet, Jerome
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supporting information; scheme or table
p. 3582 - 3585
(2010/11/05)
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- Enzymatic enantioselective reduction of α-ketoesters by a thermostable 7α-hydroxysteroid dehydrogenase from Bacteroides fragilis
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A thermostable 7α-hydroxysteroid dehydrogenase (7-HSDH) from Bacteroides fragilis ATCC 25285 was cloned and over-expressed in E. coli, and its substrate specificity and stereoselectivity toward reduction of various ketones were examined. This alcohol dehydrogenase was active toward a series of aromatic and bulky aliphatic α-ketoesters. The substituents at the phenyl ring of aromatic α-ketoesters greatly affected the activity, but their effects on enantioselectivity were minimal. The synthetic application of this enzyme was then demonstrated through the preparation of a few α-hydroxy carboxylic acid esters of pharmaceutical interest.
- Zhu, Dunming,Stearns, Jennifer Elisabeth,Ramirez, Monica,Hua, Ling
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p. 4535 - 4539
(2007/10/03)
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- An improved method for preparation of carboxylic esters using CsF- celite/alkyl halide/CH3CN combination
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A new method for efficient and chemoselective esterification of carboxylic acids in CsF-Celite/alkyl halide/CH3CN reaction system is described.
- Lee, Jong Chan,Choi, Youngsup
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p. 2021 - 2026
(2007/10/03)
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- trans-1,3-dithiane-1,3-dioxide; a chiral acyl anion equivalent. Enantioselective synthesis of α-hydroxy- carboxylic acids, esters, amides and ketones
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The reaction of (R,R)-(+)-1,3-dithiane-1,3-dioxide with aldehydes has been carried out and the dithiane dioxide moiety elaborated further. (R,R)-(+)-1,3-Dithiane-1,3-dioxide gave highly diastereoselective addition products with benzaldehyde and 3,4- dimethoxybenzaldehyde and single diastereomers were isolated in 84 and 76% purified yields respectively. Under similar conditions cyclohexane carboxaldehyde gave an easily separable mixture of diastereomers in 86% total isolated yield. The adducts were transformed into protected S- ethyl α-hydroxythioesters in 95-100% ee via a Pummerer reaction and subsequent trans-thioesterification protocol using LiSEt. Using LiSEt little racemisation occurred even with aryl substituted thioesters. Further transformations of thioesters to various α-hydroxy carboxylic acid derivatives (acids, esters, amides) without racemisation have been achieved. The approach resulted in the synthesis of the dimethyl ether of (R)-(-)-3,4-dihydroxymandelic acid in its naturally occurring form. Addition of dibutyl cuprate (derived from BuMgBr and Cu(I)Br) to the thioester gave the corresponding ketone in high yield and again without racemisation.
- Aggarwal, Varinder K.,Thomas, Abraham,Schade, Steffen
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p. 16213 - 16228
(2007/10/03)
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- Synthesis of O-Protected (R)-2-Hydroxy Aldehyde and Their Hydrocyanation
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The synthesis of O-silyl- and O-benzyl-protected (R)-2-hydroxy aldehydes (R)-6 from (R)-2-hydroxy carboxylic acids (R)-1 is described.While attempts for their diastereoselective hydrocyanation with hydrocyanic acid and (R)-oxynitrilase as catalyst have not been successful, the cyano silylation with trimethylsilyl cyanide occurred diastereoselectively with a ratio of 81:19 preferring the threo form without racemization at C-2 of the 2-hydroxy aldehyde. Key Words : (R)-2-Hydroxy aldehydes, O-protected / Hydrocyanation
- Effenberger, Franz,Hopf, Martin,Ziegler, Thomas,Hudelmayer, Jochen
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p. 1651 - 1659
(2007/10/02)
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- A FACILE SYNTHESIS OF (R)-(-)-HEXAHYDROMANDELIC ACID WITH FERMENTING BAKER'S YEAST
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Optically pure (R)-(-)-hexahydromandelic acid has been prepared stereoselectively in two steps by the asymmetric reduction of ethyl α,2-dioxocyclohexaneacetate with fermenting baker's yeast followed by Clemmensen reduction.
- Tsuboi, Sadao,Nishiyama, Emiko,Utaka, Masanori,Takeda, Akira
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p. 1915 - 1916
(2007/10/02)
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