beta-Lactam (+/-)-N-benzyl-4-phenyl-azetidin-2-one rac-6a was converted into the gamma-lactam (+/-)-traps-4,5-diphenyl-pyrrolidin-2-one rac-5 which was resolved via the preparation of diastereomers with N-phthalyl-L-alanine chloride or D-alanine chloride and its absolute configuration was determined by X-ray crystallographic analysis. This heterocycle has potential as a chiral gamma-lactam in asymmetric induction due to the steric effects of its phenyl groups. (C) 2003 Elsevier Science Ltd. All rights reserved.