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

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimN-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 molecule