Visible-light-driven Oxidation of 1,3-Dicarbonyl Compounds via Catalytic Disproportionation of TEMPO by Photoredox Catalysis

Visible light irradiation of a mixture of 1,3-dicarbonyls and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in the presence of photoredox catalysts, [Ru(bpy)(3)](2+) and [Ir(ppy)(2)(dtbbpy)](+) (bpy: 2,2'-bipyridine, ppy: 2-phenylpyridine, dtbbpy: 4,4'-di-tert-butyl-2,2'-bipyridine), afforded two types of oxidized products, i.e., alpha-oxyaminated products from acyclic 1,3-dicarbonyls and oxidatively dimerized products from cyclic 1,3-dicarbonyls. The Ir catalyst turned out to be more active than the Ru catalyst. This is a new photocatalytic oxidation of 1,3-dicarbonyls based on a single-electron-transfer process mediated by excited photoredox catalysts.