Main-chain ionic chiral polymers: synthesis of optically active quaternary ammonium sulfonate polymers and their application in asymmetric catalysis.

A condensation reaction between quaternary ammonium halide and sulfonate was first successfully applied to the synthesis of the chiral polymers. Reaction of bis(quaternary ammonium halide) with disulfonate afforded a polymer containing ionic bonds in its main chain. The chiral ionic polymers were applied to the asymmetric benzylation of N-diphenylmethylidene glycine tert-butyl ester to prepare (S)-phenylalanine derivatives in high yield with a high level of enantioselectivity.