Catalytic Enantioselective Synthesis of γ-Lactams with β-Quaternary Centers via Merging of C-C Activation and Sulfonyl Radical Migration.

Transition-metal-catalyzed C-C activation has become synthetically valuable; however, it rarely involves single-electron downstream processes. To expand the repertoire of C-C activation, here we describe the discovery of a Rh-catalyzed enantioselective C-C activation involving migration of a sulfonyl radical. This reaction directly transforms cyclobutanones containing a sulfonamide-tethered 1,3-diene moiety into γ-lactams containing a β-quaternary center with excellent enantioselectivity. This unusual process involves cleavage of C-C and N-S bonds and subsequent formation of C-N and C-S bonds. The reaction also exhibits broad functional group tolerance and a good substrate scope. A combined experimental and computational mechanistic study suggested that the reaction goes through a Rh(I)-mediated oxidative addition into the cyclobutanone C-C bond followed by a Rh(III)-triggered N-S bond homolysis and sulfonyl radical migration.