Monocarboxylates of 3‐Methylidene‐β‐lactams: Synthesis and unusual oxidative rearrangement into a spiro[azetidine‐3,3′‐pyrrolidine] derivative

Reaction of the 3‐silylated β‐lactams 1 with glycoxalates gives bis‐lactam 3, but the same reaction in the presence of 1 equiv. of Me3SiCl leads to the formation of the disilylated adducts 5. The latter is desilylated by (Bu4N)F yielding the monocarboxylates 7 of 3‐methylidene‐β‐lactams, which, with oxidizing agents, give the spiro compound 8. The structure of 8 is established by spectroscopic data and a crystal‐structure analysis.