The Cinchona alkaloid-derived quaternary ammonium salts containing 2'-N-oxypyridine and 2'-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H2O via hydrogen bonding leading to high enantioselectivity (97~> 99% ee), which provides ...
[Keizers, Peter H. J.; Saragliadis, Athanasios; Hiruma, Yoshitaka; Overhand, Mark; Ubbink, Marcellus Journal of the American Chemical Society, 2008 , vol. 130, # 44 p. 14802 - 14812]