Design of Highly Enantioselective Organocatalysts Based on Molecular Recognition
摘要:
Various organocatalysts have been designed based on molecular recognition to catalyze the asymmetric direct aldol reaction of ketones with aryl and alkyl alpha-keto acids, affording beta-hydroxyl carboxylic acids with a tertiary stereogenic center with excellent enantioselectivities of up to 98% ee. A linear effect was observed for the reaction, demonstrating a single molecule of the catalyst involved in the catalysis.
Screening of simple N-aryl and N-heteroaryl pyrrolidine amide organocatalysts for the enantioselective aldol reaction of acetone with isatin
摘要:
We have screened a range of simple N-aryl and N-heteroaryl pyrrolidine amide organocatalysts incorporating N-pyridyl and N-quinolinyl groups in the synthetically useful aldol reaction of isatin with acetone. The 'reverse amide' N-pyridyl pyrrolidinylmethyl amide catalysts proved highly catalytically active but gave disappointing enantioselectivities. However, an N-3-pyridyl prolinamide catalyst gave the aldol adduct in high yields and high enantioselectivity with up to 72% ee of the (S)-isomer. Conditions were optimised for this catalyst and in particular an additive screen identified a link between the pK(a) of the acid additive and the yield and enantioselectivity. An N-arylsulfonamide prolinamide was also identified as a catalyst for this reaction giving the (R)-enantiomer in 68% ee. (C) 2011 Elsevier Ltd. All rights reserved.
Asymmetric Organocatalytic Direct Aldol Reactions of Ketones with α-Keto Acids and Their Application to the Synthesis of 2-Hydroxy-γ-butyrolactones
作者:Xiao-Ying Xu、Zhuo Tang、Yan-Zhao Wang、Shi-Wei Luo、Lin-Feng Cun、Liu-Zhu Gong
DOI:10.1021/jo701868t
日期:2007.12.1
of organocatalysts for the asymmetric direct aldolreactions of ketones with α-keto acids were designed on the basis of molecular recognition and prepared from proline and aminopyridines. The organic molecule 8e, derived from proline and 6-methyl-2-amino pyridine, was the best catalyst, affording excellent enantioselectivities (up to 98% ee) for the direct aldolreactions of acetone or 2-butanone with
benzenesulfonic acid (DBSA) leads to highly effective and selective organocatalysts in water. The in situ generated catalysts catalyze highly stereoselective desymmetrization of prochiral ketones via directaldol reactions (up to >16:1 dr, >99% ee) in water using micelle as reaction media. The current strategy was also applied in asymmetric Michael addition leading to a catalytic system with good activity
A bifunctional organocatalytic system consisting of simple pyridine ligands containing the separate catalytic functionalities was assembled using ZnCl2. This novel metal-templated catalyst furnished high yields and stereoselectivities towards the aldol...
new porous peptide structure through a coordination-driven folding-and-assembly strategy. A porous framework with 1.5 nm-sized pores and a PII helical peptide scaffold was successfully obtained by complexation of AgNTf2 and tripeptide ligands containing the Gly-Pro-Pro sequence. The pores were modified in various ways with retention of the latent PII helical conformation of the peptide ligand.