3‐(Prop‐2‐enylidene)azetidin‐2‐one Derivatives: Synthesis, structure, and formation of 3‐spiro‐β‐lactams via Diels–Alder reactions

Reactions of 3‐silylated β‐lactams ( 1 ) with α,β‐unsaturated ketones give the propylidene‐β‐lactams 3 and the cycloalkenylidene derivatives 5 . Structure and configuration are elucidated by spectroscopic methods, and the reactivity is discussed. While compounds 5 do not react with dienophiles, the ( Z )‐isomers of 3 are the favored substrates for Diels‐Alder reactions yielding the spiro compounds 6 and 7 .