Chiral 2-aminobenzimidazole bifunctional organocatalysts: effect of di-CF3 and TFA on catalytic mechanisms
摘要:
(S,S)-trans-Cyclohexanediamine-5,7-di-CF3-benzimidazole (3b) was developed as a new chiral bifunctional organocatalyst and successfully applied to Michael addition of diethyl malonate to nitroolefins (up to 99%, 98% ee) under neutral condition. Systematic investigation on the catalytic mechanism revealed that the role of the guanidine moiety and the dimethylamine moiety in catalysts might be reversed with respect to Bronsted/Lewis acidic or basic functionalities, depending on the reaction conditions (neutral or TFA co-catalyst). Generally, di-CF3 group substituted 2-aminobenzimidazole catalysts in neutral condition and non-substituted 2-aminobenzimidazole catalysts in co-catalyst (TFA) condition give high chemical yield and enantioselectivity. (C) 2011 Elsevier Ltd. All rights reserved.
A series of chiral polysulfonate cyclohexyldiamine-Ni(II) catalysts were prepared via sulfur (VI) fluoride exchange click-reactions. The catalysts exhibited good catalytic activity and enantioselectivity in the Michaeladdition of malonates to nitroalkenes. The excellent recyclability of the catalysts was demonstrated via the reuse of the privileged catalyst 7a for ten times. The results provide a
Design, preparation, and studies of a family of new organiccatalysts are presented. The design of the catalysts is inspired by the ability of DNA nucleobases to develop precise and explicit hydrogen bonds. We have shown that this phenomenon can be used to create a useful organiccatalyst that demonstrates a recognition pattern similar to those of common organic substrates. A selected bifunctional
介绍了一系列新型有机催化剂的设计、制备和研究。催化剂的设计灵感来自于 DNA 核碱基发展精确和明确的氢键的能力。我们已经表明,这种现象可用于创建一种有用的有机催化剂,该催化剂显示出类似于常见有机底物的识别模式。基于鸟嘌呤结构的选定双功能催化剂已被证明可催化 1,3-二羰基化合物与各种硝基烯烃的共轭加成,从而以良好的产率和对映选择性提供产品。
Physical Organic Study of StructureâActivityâEnantioselectivity Relationships in Asymmetric Bifunctional Thiourea Catalysis: Hints for the Design of New Organocatalysts
Correlations of pKa with catalytic activity and stereoselectivity were determined and linear free energy relationships (LFERs) were observed for both pKa−log (k) and pKa−log (R/S) correlations in meta‐ and/or para‐substituted aromatic thioureas (see figure). These results provided a basis for new catalyst development and several improved catalysts were identified in our initial attempts.
酸度效应:确定了p K a与催化活性和立体选择性之间的相关性,并在meta ‐中的p K a -log(k)和p K a -log(R / S)相关性中观察到线性自由能关系(LFER)。和/或对位取代的芳族硫脲(见图)。这些结果为新催化剂的开发提供了基础,并且在我们最初的尝试中发现了几种改进的催化剂。