Visible Light-Mediated Installation of Halogen Functionalities into Multiple Bond Systems

Abstract

Photoredox catalysis has emerged as a useful tool for organic, synthetic, and material chemists to approach target molecules with new functionalities and structural complexity. This review focuses on the recent advances in the visible light-promoted halogenation and trifluoromethylation/difluoromethylation of multiple bonds. Halogen functionalities are important chemical handles and building blocks in organic synthesis. Both electrophilic addition of halogens and radical halogenations are widely utilized in organic synthesis to install halogen functionalities. However, harsh conditions and low regioselectivity could present challenges. Despite these concerns, recent efforts have led to obvious advances in the visible light-promoted halogenation of multiple bonds. In this context, we address the recent achievements in the visible light-mediated installation of different types of halogen-containing functionalities, which include (i) halogenation of unsaturated carbon-carbon bonds, (ii) trifluoromethylation and difluoromethylation of π-systems, and (iii) photoredox cyclization by insertion of fluorine sources. A variety of active catalytic species in the photoredox halogenations are also discussed in terms of their unique reactivity for the future development of highly practical and efficient processes.