A series of pyrrolidine derivatives with beta-amino alcohol moieties prepared from (S)-proline were found to catalyze the enantioselective addition of diethylzinc to aldehydes to yield optically active secondary alcohols with high enantioselectivities. A mechanism accounting for the configurational change with the bulkiness of chiral ligands is proposed. (C) 1999 Elsevier Science Ltd. All rights reserved.