β-Lactams or γ-lactams by 4-exo-trigor 5-endo-triganionic cyclisation of lithiated acrylamide derivatives

Substituted acrylamide derivatives of benzylamine are lithiated α to nitrogen by LDA. The benzyllithium thus formed undergoes either 5-endo-triganionic cyclisation, formally by intramolecular conjugate addition to the acrylamide, to yield 5-membered lactams, or, if the acrylamide bears a β-electron withdrawing group, 4-exo-trigcyclisation to a β-lactam.