Highly enantioselective biomimetic intramolecular dehydration: kinetic resolution of β-hydroxy ketones catalyzed by β-turn tetrapeptides
摘要:
Racemic beta-hydroxy ketones were kinetically resoluted into the enantiopure isomers and (E)-alpha,beta-unsaturated ketones using catalytic asymmetric intramolecular dehydration for the first time. Synthetic tetrapeptides were used to imitate fatty acid dehydratases to efficiently discriminate racemic beta-hydroxy ketones, enantioselectively catalyze the intramolecular dehydration, and result in highly enantioenriched beta-hydroxy and (E)-alpha,beta-unsaturated ketones in the environmentally benign process. Mechanistically, the high discrimination of the racemic substrates and successive enantioselective dehydration are highly dependent on the cooperative catalysis of the NH2 and COOH groups of the peptide. (C) 2013 Elsevier Ltd. All rights reserved.
An economical, simple, and efficient direct aldol reaction via the double activation of both aldehydes and ketones by ammonia has been developed. An unprecedented tandem Mannich reaction was observed when hydroxybenzaldehydes, pyrrole-2-carboxyaldehyde, and indole-3-carboxyaldehyde were employed to afford 2,2-dimethyl-6-aryl-4-pyrilidinones in moderate to good yields.
Tandem Catalysis by Lipase in a Vinyl Acetate-Mediated Cross-Aldol Reaction
作者:Manjeet Kumar、Bhahwal A. Shah、Subhash C. Taneja
DOI:10.1002/adsc.201000980
日期:2011.5
The lipase Novozym435 (0.6% w/w) was used in tandem with organocatalysts in a first vinyl/isopropenyl acetate‐mediated aldol reaction. The reaction was facilitated through the lipase‐catalyzed in situ generation of acetaldehyde/acetone. The important features of the present methodology include the mild and facile reaction conditions, regenerability of the lipase, comparatively high yields and minimal
The Zn–proline complex is shown to catalyze the aldolreaction of acetone and a wide range of arenecarbaldehydes in aqueous media, accepting even deactivated arenecarbaldehydes such as methoxybenzaldehydes in good yields. Enantiomeric excesses of up to 56 % could be obtained with 5 mol-% of the catalyst at room temperature, and up to 66 %
Chiral Gating for Size- and Shape-Selective Asymmetric Catalysis
作者:Xiaowei Li、Yan Zhao
DOI:10.1021/jacs.9b06619
日期:2019.9.4
A poor or mediocre stereoselectivity is a key roadblock for a chiral cata-lyst to find practical adoptions. We report a facile method to create a tunable chiral space near a chiral catalyst to augment its selectivity. The space was created rationally through templated polymerization within cross-linked micelles, using readily available amino acid derivatives. It provided gated entrance of reactants
较差或中等的立体选择性是手性催化剂找到实际应用的主要障碍。我们报告了一种在手性催化剂附近创建可调手性空间以提高其选择性的简便方法。该空间是通过交联胶束内的模板聚合合理创造的,使用容易获得的氨基酸衍生物。它为反应物提供了进入催化剂的门控入口,使普通的脯氨酰胺能够以尺寸和形状选择性的方式以优异的产率和 ee 催化水中的羟醛缩合。
Chitosan hydrogel: A green and recyclable biopolymer catalyst for aldol and Knoevenagel reactions
作者:K. Rajender Reddy、K. Rajgopal、C. Uma Maheswari、M. Lakshmi Kantam
DOI:10.1039/b610355c
日期:——
Chitosan hydrogel is efficiently utilized as an organocatalyst for aldol and Knoevenagel reactions, providing the products in high yields with a high chemoselectivity under biphasic conditions. The catalyst was recovered by simple filtration and reused several times without significant loss of activity.