Dimeric cinchona ammonium salts with benzophenone linkers: enantioselective phase transfer catalysts for the synthesis of α-amino acids.

Chiral phase transfer catalysts of dimeric cinchona ammonium salts linked with a benzophenone bridge showed high enantioselectivity in the α-alkylation of a glycinate ester under mild industry-applicable conditions: 0.5 mol% PTC and near equivalents of alkyl halide. A dual function of the dimeric quinuclidiniums was proposed for the high efficiency.