Visible Light‐induced Functionalization of C−H Bonds: Opening of New Avenues in Organic Synthesis

Abstract In the last three decades, the resurgence and astonishing evolution of visible light‐mediated unreactive C−H bond functionalization has led to a sustainable and greener approach for introducing various moieties into imperative organic frameworks without the need for substrate preactivation. Unlike traditional electrophilic or nucleophilic reactions, the free radical mechanism of photoredox catalysis opens up new routes to achieve unprecedented C−H bond functionalization. In this context, single‐electron transfer or energy transfer interactions among exogenous photocatalysts, i. e., TM photocatalysts or organic dye photosensitizers, etc., in their excited state with the targeted substrate, thus generates active radical species, which encompasses the further elusive reaction pathways. This review covers the distinct radical generation methods via photoredox catalysis to trigger the C−H bond cleavage through visible light irradiation. Herein, we provide an overview of progress made in the last five years in visible‐light‐induced C−H bond functionalization, which may help chemists to envision the significant chemical transformations in molecular complexity.