The past, present, and future of the Yang reaction

Photoexcited ketones have diradical characteristics and are functionally similar to high-spin metal-oxo species that are frequently used to catalyze C-H oxidation. First discovered by Yang in 1958, photoexcited ketones can abstract a hydrogen atom from hydrocarbons inter-or intramolecularly. Coupling with atom-transfer, group-transfer, or radical addition, the Yang reaction can be used to achieve various types of C-H functionalization. We provide in this article an overview of triplet ketone-mediated or catalyzed C-H functionalization reactions.