ortho‐Alkylation of Pyridine N‐Oxides with Alkynes by Photocatalysis: Pyridine N‐Oxide as a Redox Auxiliary

A photocatalyzed ortho‐alkylation of pyridine N‐oxide with ynamides and arylacetylenes has been developed, which yields a series of α‐(2‐pyridinyl) benzyl amides/ketones. Mechanistic studies, including electrochemical studies, radical‐trapping experiments, and Stern–Volmer fluorescence quenching studies demonstrate that pyridine N‐oxide serves as both a redox auxiliary and radical acceptor to achieve the mild photocatalytic single‐electron oxidation of carbon–carbon triple bonds with the generation of a cationic vinyl radical intermediate. Redox auxiliary for alkynes: An ortho‐alkylation of pyridine N‐oxide with alkynes, including ynamides and arylacetylenes, has been achieved by organic photocatalysis, which provides access to a series of α‐(2‐pyridinyl) benzyl carbonyl compounds. Pyridine N‐oxide functions as both a redox auxiliary and radical acceptor to achieve the challenging photocatalytic single‐electron oxidation of the carbon–carbon triple bond.