Metallation of N-Substituted β-Lactams. A Method for the Introduction of 3-Substituents into β-Lactams

N-Alkyl and N-aryl β-lactams yield lithio carbanions upon reaction with lithium diisopropylamide in tetrahydrofuran at −78°. These lithio salts react with a variety of electrophiles (e.g. ketones, esters, reactive alkyl halides) to give the 3-substituted derivatives in fair to good yield. The procedure is useful for the preparation of rather complex 3-substituted β-lactams from readily available simple derivatives.