An Efficient Method of Synthesis of Isoxazolidine-Fused β-Lactams via Base-Promoted Cyclization—Ring Opening of Carbamoylspirocyclopropane Isoxazolidines.

A novel type of β-lactame derivatives (IV) can be synthesized by base-promoted cyclization-cyclopropane ring opening of isoxazolidines (III) which in turn are readily prepared by 1,3-dipolar cycloaddition of C-carbamoyl nitrones (I) with methylenecyclopropanes (II).