Photoredox manifold for dehydrogenative coupling using protons as oxidants

The direct coupling of two unfunctionalized molecules under mild conditions embodies an ideal in synthetic chemistry. In this study, we report a metal-free photocatalytic process for arene C-H functionalization that employs an acridinium-type catalyst and produces dihydrogen as the only by-product. Throughout the catalytic cycle, the catalyst acts as an oxidizing agent, a hydrogen atom transfer agent, and a proton-reducing agent, enabling a cross-dehydrogenative transformation without the need for external oxidants. The reaction is conveniently performed using visible light, and the high oxidation potential of the catalyst allows it to engage even electron- deficient arene substrates. The catalytic mechanism disclosed herein can become a general logic for developing various cross-dehydrogenative reactions adaptable for pharmaceutical and material sciences.