P(NMe2)3 mediated cyclopropanation of α-methylene-β-lactams for rapid syntheses of spirocyclopropyl β-lactams.

An expedient cyclopropanation of α-methylene-β-lactams with α-ketoesters mediated by P(NMe2)3 has been developed. This reaction enables rapid access to a series of functionalized spirocyclopropyl β-lactams in good yields from bench-stable starting materials under mild conditions. The experimental results indicated that the C3-substituent of the α-methylene-β-lactam not only significantly impacted the reaction efficiency and stereochemistry but also played a pivotal role in determining the chemoselectivity of the reaction.