Principles and Applications of Photoredox Catalysis: Trifluoromethylation and Beyond

Photoredox catalysis has attracted the increasing attention of chemists in various fields from the viewpoints of green chemistry, solar chemistry, clean redox processes, and radical chemistry. Discussion of the principles and features of photoredox catalysis will be followed by illustration using typical examples with emphasis on the reactions developed in the authors' laboratory which proceed via an oxidative quenching cycle accompanying reduction of external substrates in the first stage. Photoredox catalysis turns out to be quite effective for trifiuoromethylation of olefinic substrates with electrophilic trifluoromethylating reagents such as Umemoto's and Togni's reagents, le-reduction of which generates the key intermediate, trifluoromethyl radical. Key features of photoredox catalysis will be discussed in terms of visible light-driven reactions, radical reactions, redox-neutral system and atom economy. The concept can be extended to other radical systems such as N- and C-centered radicals. This review article will be closed with an overview of future prospects for photoredox catalysis.