Deconstructing quinine. Part 1. Toward an understanding of the remarkable performance of cinchona alkaloids in asymmetric phase transfer catalysis

A study of catalyst structure-activity/selectivity relationships for Cinchona alkaloid-based asymmetric phase transfer catalysis (APTC) is described. An array of substituent modifications at C(9) and the quinuclidine nitrogen were introduced to examine the role of steric and electronic effects on rate and selectivity. The synthesis of the catalysts began with manipulation of the C(9) hydroxyl group followed by alkylation of the quinuclidine nitrogen to generate the quaternary ammonium salt. Catalysts that contained large substituents attached to the quinuclidinium nitrogen were found to be the most selective and those in which the hydroxyl group was protected generally afforded faster catalysts. The presence of a polar group at C(9) significantly impacted catalyst activity.