Transition metal-free cross-coupling reactions to form carbon–heteroatom bonds

The formation of carbon–heteroatm bond is the key step of synthesis of numerous organic compounds, including socially important products such as pharmaceuticals, crop protection agents and organic functional materials. These reactions proceed most efficiently when catalyzed by compounds of transition metals, first of all palladium. However, this approach has considerable drawbacks, in particular, high cost and toxicity of transition metal compounds and harsh reaction conditions required in some cases, resulting in limited functional group tolerance. This review describes the recent advances in the development of methodology of transition metal-free carbon–heteroatom bond-forming cross-coupling. It is shown that single-electron transfer and homolytic bond cleavage result in the generation of highly reactive radical and/or radical ion intermediates, enable the formation of new carbon–heteroatom bonds. These intermediates are generated using either visible light or electricity as energy sources or simple organic compounds acting as electron donors. Methods for carbon–heteroatom bond formation based on radical reactions proceeding under mild conditions and in the presence of labile functional groups are considered. The key mechanistic aspects of the reactions are highlighted. The review mainly covers the original publications of the current decade. The bibliography includes 302 references.