In this report, we demonstrate that visible-light-induced thiourea photoacids catalyze C–C bond-forming reactions. Upon photoirradiation, Schreiner’s thiourea [(N,N′-bis­[3,5-bis­(trifluoromethyl)­phenyl]-thiourea] catalyzes the double Friedel–Crafts addition of indoles to aldehydes and isatins to form the corresponding triarylmethanes and 3,3′-diarylindolin-2-ones. This protocol is amenable to a wide range of aldehyde and isatin electrophiles, as well as a variety of electronically diverse indoles. Mechanistic studies show that light is required for reaction initiation.

Photoacids are molecules that become more acidic upon the absorption of light. This short review highlights recent advances in the use of photoacids as catalysts for organic synthesis. Photoacid-catalyzed­ transformations discussed herein include: Protonation, glycosylation, acetalization, and arylation reactions.1 Introduction2 Protonation: Excited-State Proton Transfer (ESPT)3 Glycosylation4 Acetalization5 Friedel–Crafts Arylation6 Additional C–C and C–S Bond-Forming Reactions7 Conclusion