Photoorganocatalyzed Direct Hydrogen Atom Transfer (HAT): A Tool for Transition Metal-Free C-C Bond Formation

Photocatalytic hydrogen atom transfer (HAT) is a valid tool for the functionalization of aliphatic C-H bonds in a mild way, offering a straightforward path to ameliorate the step and atom economy of synthetic processes. Thus, carbon-centered radicals are smoothly generated via a homolytic C-H cleavage and they are mainly used to forge valuable C-C bonds. Among the photocatalysts available, both metal-containing derivatives and organic compounds are viable options in some respect. However, the adoption of the latter class of photocatalysts is appreciated from an environmental point of view, since the desired products are free from metal contaminants. In this frame, the aim of this article is to collect the processes (mainly the most recent ones) making use of a photoorganocatalyst (POC_HAT) for the generation via HAT of carbon-centered radicals, in turn, used for diverse synthetic purposes. These include hydroalkylation and hydroacylation of olefins, along with the preparation of alkenes, alkynes, and substituted heteroaromatics.