Cobalt-catalyzed carbonylative formal cycloaddition of cyclopropenes and imines toward β-lactams

A cobalt-catalyzed carbonylative formal [2 + 2] cycloaddition of cyclopropenes with imines using carbon monoxide as a C1 source has been developed. • A cobalt-catalyzed carbonylative formal [2 + 2] cycloaddition of cyclopropenes with imines has been developed. • Alkenyl ketenes were generated as the key intermediates. • Various allylic β-lactams were obtained in good to excellent yields. • The reaction proceeds under mild conditions with high yields and wide substrate tolerance. We herein report a cobalt-catalyzed stereoselective carbonylative formal [2 + 2] cycloaddition of cyclopropenes with imines, providing efficient access to functionalized allylic β-lactams. The transformation proceeds through in situ generation of β-alkenyl ketene intermediates via carbon monoxide insertion into strained cyclopropenes. A broad range of substrates is tolerated, affording the corresponding β-lactams in generally good yields with high stereoselectivity under relatively mild conditions.