Photochemical strategies for C–N bond formation via metal catalyst-free (hetero) aryl C(sp²)–H functionalization

The development of efficient and mild methods to assemble C–N bonds represents an important and appealing goal in modern synthetic chemistry. Recently, (hetero) aryl C(sp2)–H functionalization involving a radical process has emerged as an ideal and powerful route to construct C–N bonds, along with diminished cost and waste. As a simple and green methodology, photocatalysis offers selective and efficient access to the generation of radical species. This review presents state-of-the-art examples of photochemical strategies for C–N bond formation via metal catalyst-free (hetero) aryl C(sp2)–H functionalization since 2015. The discussion is divided into six sections according to the type of nitrogen sources and emphasis is placed on the related reaction mechanisms.