A straightforward method is developed for the synthesis of enantiopure (3S,4R)-3-amino-4-alkyl-2-piperidinone derivatives, six-membered lactam-bridged dipeptides, via highly diastereofacial selective 1,4-addition of organocuprate to the chiral oxazolidine alpha,beta -unsaturated ester 1 as the key step. (C) 2001 Elsevier Science Ltd. All rights reserved.