Cyclative Carbon Quaternization of Alkyl Boronic Esters via Copper-Catalyzed Aminyl Radical Transfer

Despite the rich chemistry of alkyl boronic esters (alkyl Bpins) in C–B bond transformations, carbon quaternization via concurrent C–B and C–H bond scission on the boron-substituted carbon has remained elusive. Herein, we report a copper-catalyzed aminyl radical-mediated cyclative C-quaternization of alkyl Bpins with acrylamides to access valuable carbo- and spirocyclic scaffolds. Central to this transformation is a sequential C–B/C–H bond-cleavage, in which ART triggers C–B cleavage and HAT enables site-selective C–H functionalization. The method has a broad substrate scope, high functional group tolerance, and exquisite site selectivity and allows late-stage diversification of drugs and natural products. Mechanistic studies and DFT calculations were conducted to elucidate the underlying reaction mechanism. These studies support the generation of aminyl radicals via Cu–N bond homolysis, which is effective for ART, and rationalize selective 1,5-HAT and copper-mediated PCET in the key cyclization step.