Chiral relay in NHC-mediated asymmetric β-lactam synthesis I; substituent effects in NHCs derived from (1R,2R)-cyclohexane-1,2-diamine
摘要:
The synthesis of a range of C-2-symmetric imidazolinium salts from (1R,2R)-cyclohexane-1,2-diamine, and an evaluation of the reactivity and asymmetric induction of the derived NHCs as catalysts for the asymmetric synthesis of beta-lactams, is reported. In this series, optimal enantioselectivity (up to 70% ee) is observed using N-benzyl or N-1-naphthylmethyl-substituted NHCs, consistent with a chiral relay effect operating to dictate the stereochemical outcome of this reaction. (C) 2010 Elsevier Ltd. All rights reserved.
The asymmetric synthesis of α-substituted α-methyl and α-phenyl phosphonic acids: Design, carbanion geometry, reactivity and preparative aspects of chiral alkyl bicyclic phosphonamides
作者:Youssef L. Bennani、Stephen Hanessian
DOI:10.1016/0040-4020(96)00829-0
日期:1996.10
The design, preparation, structural and spectroscopic analyses of topologically unique and enantiomerically pure alkylphosphonamides are described. In the case of α-ethyl and α-benzyl phosphonamides, the geometry of both the secondary and tertiary carbanions was determined to be planar through deprotonation/deuteration/alkylation experiments. Stereoselective alkylations of such systems proceeded in
steric tuning of two amidinate units as well as multiple coordination on the Zn atoms play a key role in achieving high enantioselectivity (up to 98% ee) and unique chemoselectivity. The present catalyst exhibited the preferential alkylation of α-ketoesters even in the presence of aldehydes.
X-ray crystallography, infrared absorption and Raman scattering were applied to study the influence of Zn(II) or H+ on the amidic bond. (R,R)-1,2-diacetamidocyclohexane (DAACH) was chosen as a conformationally strained chiral building block including two amide bonds; this model is hoped to be not too far from a peptide and gives easily crystalline complexes. Crystallographic structures of DAACH molecule
应用 X 射线晶体学、红外吸收和拉曼散射来研究 Zn(II) 或 H+ 对酰胺键的影响。(R,R)-1,2-二乙酰氨基环己烷 (DAACH) 被选为包含两个酰胺键的构象应变手性结构单元;希望这个模型离肽不太远,并且容易产生结晶复合物。研究了 DAACH 分子 (1)、DAACH/ZnBr2 (2) 和 DAACH/HBr3 (3) 复合物的晶体结构。DAACH 络合 Zn 是由于酰胺键的超极化。1-3 的 IR 和拉曼研究与 X 射线结果一致。这可能是研究金属/蛋白质相互作用或多肽酸性变性的模型
N,N′-Dialkylated 1,2-diamine derivatives as new efficient ligands for RuCl2(PPh3)3 catalyzed asymmetric transfer hydrogenation of aromatic ketones
Chiral N,N'-dialkylated cyclohexanediamine derivatives ligands have been synthesized and used in an asymmetric transfer hydrogenation of aryl ketones. Optically active alcohols with up to 93% enantiomeric excess were obtained in high yield. (C) 2002 Published by Elsevier Science Ltd.