A Novel Dieckmann-Type Cyclization, the Final Step of the Synthesis of a Carbacephem Derivative

The treatment of the triacylamine, methyl 4-(dibenzoyl-aminocarbonylethyl)-2-oxoazetidine-1-acetate (2), with sodium bis(trimethylsilyl)amide leads to an unprecedented Dieckmann-type ring closure to form the anion of the carbacephem derivative, methyl 3-hydroxy-1-carbacephem-4-carboxylate, (3)