Phenylglyoxylic Acid: An Efficient Initiator for the Photochemical Hydrogen Atom Transfer C-H Functionalization of Heterocycles.

C-H functionalization at the α-position of heterocycles has become a rapidly growing area of research. Herein, a cheap and efficient photochemical method was developed for the C-H functionalization of heterocycles. Phenylglyoxylic acid (PhCOCOOH) could behave as an alternative to metal-based catalysts and organic dyes and provided a very general and wide array of photochemical C-H alkylation, alkenylation, and alkynylation, as well as C-N bond forming reaction methodologies. This novel, mild, and metal-free protocol was successfully employed in the functionalization of a wide range of C-H bonds, utilizing not only O- or N-heterocycles, but also the less studied S-heterocycles.