Visible‐Light Catalyzed Functionalizations of Allylic C–H Bonds

Comprehensive Summary Allylic scaffolds are prevalent in natural products and bioactive molecules. The direct functionalization of inert C–H bonds at allylic position provides an ideal alternative to access functionalized allylic substructures with diverse coupling partners with step‐ and atom‐economy. In particular, visible‐light catalyzed direct functionalizations of allylic C–H bonds have emerged as a versatile platform for transforming C–H bond to carbon‐carbon and carbon‐heteroatom bonds with the control of chemo‐, regio‐, and enantioselectivity control under mild conditions. Significant progress on this topic has been achieved through different mechanistic paradigms, including photoactivation of organo‐transition metal intermediates, hydrogen atom transfer (HAT), single‐electron transfer (SET), electron donor–acceptor (EDA) complex excitation, radical addition as well as combining photoredox with other catalytic methods. Taken together, this review focuses on the development of C–H functionalization by visible‐light catalysis with an emphasis on reaction development and mechanistic considerations. Moreover, further challenges and future efforts for this area are also discussed.