Photoinduced intermolecular hydrogen atom transfer reactions in organic synthesis

Hydrogen-atom transfer (HAT) provides straightforward methods to generate open-shell radical intermediates from R-H (R = C, Si, etc.) bonds and offers unique opportunities for green and sustainable synthesis. Traditional HAT protocols required harsh conditions and relied on the use of harmful reagents such as Cl2 and peroxides. An emerging strategy is photoinduced intermolecular HAT, in which transformations can be driven by photocatalysis under mild conditions. In recent years, photoinduced intermolecular HAT reactions have seen substantial development of their versatility, efficiency, and selectivity. This review summarizes recent advances (up to December 2020) in this rapidly expanding research area. The representative examples provided are classified according to the active species responsible for hydrogen atom abstraction. The reactivity, selectivity, and established transformations for each type of active species are briefly summarized. This review aims to provide guidance for the application of photoinduced HAT in R-H functionalization reactions and to inspire further progress in this research area.