The nature of quaternary ammonium salt and their function as phase-transfer catalyst is well-established. Chiral catalysts in phase-transfer reaction to achieve absolute asymmetric synthesis have been attracted tremendous scientists’ interests.

The majority of the published work used chiral salts which contained chirality in the carbon skeleton or combination of chirality in both nitrogen and carbon. The significance of N-chirality in quaternary ammonium does not seem to be specifically addressed in asymmetric reactions.

Prof. ZHANG Guolin’s group from Chengdu Institute of Biology, Chinese Academy of Sciences, is interested in the study of asymmetric inductive effect of the N-stereogenic centre in quaternary ammonium salts. Previously, they synthesized N-chiral quaternary ammonium salts from amino acids and successfully separated the diasteromers, results were published in Helvetica Chimica Acta, 2009, vol. 92, 677-688.

 

To further investigate the asymmetric inductive effects of the N-stereogenic centre in quaternary ammonium salts, they have synthesized four quaternary ammonium salts with C-chiral center for control.

These salts together with four previously synthesized quaternary ammonium salts containing both N- and C- chiral centers, were applied as asymmetric phase-transfer catalysts in the enantioselective alkylation of N-(diphenylmethylene)glycine tert-butyl ester with benzyl bromide.

 

The relationships between the  values of the products and the structures of the catalysts were investigated. This project was financial supported by National Sciences Foundation of China (20672108) and Chengdu Institute of Biology, Chinese Academy of Sciences.