Visible-Light-Enabled Allylic C–H Oxidation: Metal-free Photocatalytic Generation of Enones

A practical and efficient method has been established for the direct oxidation of allylic C–H bonds catalyzed by visible-light-enabled photoredox agents. This protocol uses oxygen as the sole oxidant under metal-free conditions at room temperature and produces functionalized enones. When combined with acid-promoted dehydration, this benign and mild method enables the production of meta-functionalized phenols from simple cyclohexenols. A key to this reaction is the choice of tetrabutylammonium bromide as a hydrogen atom transfer cocatalyst.