On the question of the diastereoselective alkylation of 4-unsubstituted 3-amino beta-lactams. A concise synthesis of alpha-branched alpha-amino beta-lactams and their coupling with alpha-amino acid esters

The reaction of [(4S)-2-oxo-4-phenyloxazolidin-3-yl]acetic acid chloride wi th N-methylidene-bis-[(trimethylsilyl)methyl] amine and triethylamine in re fluxing chloroform leads to a 4-unsubstituted beta-lactam able to undergo h ighly asymmetric alkylations at the alpha-position of the beta-lactam ring. The resulting adducts can be efficiently transformed into N-unsubstituted alpha-branched 3-amino beta-lactams as the cyclisized forms of alpha-branch ed beta-aminoalanines or transformed into their imide N-Boc derivatives, wh ich are suitable substrates for non-proteinogenic peptide synthesis, by rea ction with alpha-amino esters. (C) 2000 Elsevier Science Ltd. All rights re served.