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L-Pipecolinic acid derived Lewis base organocatalyst for asymmetric reduction of N-aryl imines by trichlorosilane: effects of the side amide group on catalytic performances
Department of Pharmaceutics Engineering, Xihua University, Chengdu, China
E-mail: zhouyuwang77@gmail.com
; Fax: +86-028-8772-0552
; Tel: +86-028-8772-0552
b
Natural Products Research Center, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China
E-mail: sunjian@cib.ac.cn
; Fax: (+86) 28-85222753
; Tel: (+86) 28-85222753
Org. Biomol. Chem., 2013,11, 787-797
DOI:
10.1039/C2OB26772A
Received
08 Sep 2012,
Accepted
11 Nov 2012
First published online
12 Nov 2012
A series of N-formamides derived from pipecolinic acid have been synthesized and tested as Lewis base catalysts for the enantioselective reduction of N-aryl imines by trichlorosilane. Through the investigation of the structure–efficacy relationship between the side amide group and catalytic performance, several highly effective catalysts were discovered. In particular, arylamido-type catalyst 5i and non-arylamido-type catalyst 6c exhibited high reactivity and enantioselectivity, furnishing the reduction of a wide variety of N-aryl imines with high isolated yields (up to 98%) and ee values (up to 96%) under mild conditions. Moreover, these two catalysts complement each other in terms of their tolerances to nonaromatic ketimines and non-methyl ketimines.