Synthesis of cinchonidinium salts containing sulfonamide functionalities and their catalytic activity in asymmetric alkylation reactions

Various kinds of 4-(bromomethyl)benzenesulfonamides were prepared as quaternization reagent of cinchonidine. Cinchonidinium salts obtained from the quaternization of cinchonidine with 4-(bromomethyl)benzenesulfonamide showed highly enantioselective catalytic activity in the asymmetric benzylation of N-(diphenylmethylene)glycine tert-butyl ester. The corresponding phenylalanine derivative was obtained in high yield with a high level of enantioselectivity, up to 98% ee.