Photoinduced generation of ketyl radicals and application in C–C coupling withoutexternal photocatalyst

Abstract

Single-electron reduction of a carbonyl by photoredox catalysis enables the generation of ketyl radicals, providing a benign procedure for constructing C–C bonds. However, external photocatalysts are required. In this paper, photoinduced generation of ketyl radicals and application in C–C coupling are reported, which require no use of any external photocatalyst. Irradiation of carbonyl with purple light in the presence of a tertiary amine generates highly reactive ketyl radicals, enabling a series of important reactions in synthetic chemistry, such as the reductive coupling of aldehydes, ketones, and imines, the allylation of aldehydes, the Barbier reaction, reductive arylation, and aldehyde–aniline coupling. We also present evidence to support the ketyl radicals being formed via photoinduced intermolecular electron transfer from the tertiary amine to aryl aldehydes.