Efficient synthesis of 4-vinyl α,β-unsaturated γ-lactams by ring-closing enyne metathesis reactions

The ring-closing enyne metathesis reaction of alkyl 2-substituted-2-(N-alkynyl acrylamido)esters using the first-generation Grubbs’ catalyst afforded five-membered lactams bearing a 1,3-diene moiety in high isolated yields. In the reaction process, the presence of ethylene gas is essential.