Noncovalently Supported Heterogeneous Chiral Amine Catalysts for Asymmetric Direct Aldol and Michael Addition Reactions

• Published in: Chemistry : a European journal Vol. 14; no. 4; pp. 1273 - 1281
• Main Authors: Luo, Sanzhong, Li, Jiuyuan, Zhang, Long, Xu, Hui, Cheng, Jin-Pei
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-01-2008; WILEY‐VCH Verlag
• Subjects: Aldehydes - chemistry; aldol reaction; Amines - chemistry; Catalysis; heterogeneous catalysis; Michael addition; noncovalent immobilization; organocatalysis; Stereoisomerism
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200701129

A new strategy for the immobilization of asymmetric organocatalysts by combining polystyrene (PS)/sulfonic acids and chiral amines in situ through acid–base interactions is presented. The PS/sulfonic acids play a dual role as catalyst anchors and modulators for activity and stereoselectivity. Different types of polymeric sulfonic acids were examined and 1 % divinylbenzene (DVB) cross‐linked PS/sulfonic acid 1 e with a medium loading of sulfonic acid moieties was found to be the optimal support. Furthermore, the noncovalency of this system allows combinatorial screening of optimal catalysts for the targeted reactions. In this regard, highly efficient and enantioselective heterogeneous catalysts were identified for the asymmetric direct aldol and Michael addition reactions. The catalysts could be easily recovered by filtration and reused for six cycles with similar stereoselectivity but slightly decreased activity. Significantly, the deactivated catalysts could be regenerated following an acidic washing/amine recharging procedure.
Keep it simple: Asymmetric heterogeneous organocatalysts can be simply realized in situ through the complexation of polystyrene/sulfonic acids and chiral amines through acid–base interactions and were applied to the aldol and Michael reactions (see scheme). The noncovalency of this heterogenization strategy enables simple catalyst preparation, combinatorial screening, and facile reuse and reactivation of the catalyst.