Photochemical Carbopyridylation of Alkenes Using<i>N</i>‐Alkenoxypyridinium Salts as Bifunctional Reagents

Abstract

Abstract N‐Alkenoxypyridinium salts have been used as synthons for the umpolung reaction of enolates for the preparation of α‐functionalized carbonyl compounds. In contrast, we found that the photoreduction of N‐alkenoxypyridinium salts generates α‐carbonyl radicals after cleavage of the N−O bond, thereby allowing simultaneous incorporation of α‐keto and pyridyl groups across unactivated alkenes. In the process, the formed α‐carbonyl radicals engage unactivated alkenes to afford alkyl radical intermediates poised for subsequent addition to pyridinium salts, which ultimately affords a variety of γ‐pyridyl ketones under mild reaction conditions. This transformation is characterized by a broad substrate scope and good functional‐group compatibility, and the utility of this transformation was further demonstrated by the late‐stage functionalization of complex biorelevant molecules.