Photochemical Carbopyridylation of Alkenes Using N-Alkenoxypyridinium Salts as Bifunctional Reagents

N-Alkenoxypyridinium salts have been used as synthons for the umpolung reaction of enolates for the preparation of alpha-functionalized carbonyl compounds. In contrast, we found that the photoreduction of N-alkenoxypyridinium salts generates alpha-carbonyl radicals after cleavage of the N-O bond, thereby allowing simultaneous incorporation of alpha-keto and pyridyl groups across unactivated alkenes. In the process, the formed alpha-carbonyl radicals engage unactivated alkenes to afford alkyl radical intermediates poised for subsequent addition to pyridinium salts, which ultimately affords a variety of gamma-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.