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.