(beta)-Lactams or (gamma)-lactams by 4-exo-trig or 5-endo-trig anionic cyclisation of lithiated acrylamide derivatives

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