Visible-Light-Induced Regioselective C–H Sulfenylation of Pyrazolo[1,5‑a]pyrimidines via Cross-Dehydrogenative Coupling

A visible-light-induced cross-dehydrogenative methodology has been developed for the regioselective sulfenylation of pyrazolo[1,5-a]pyrimidine derivatives. Rose bengal, blue LEDs, KI, K2S2O8, and DMSO are all essential for this photocatalytic transformation. The protocol is applicable for the synthesis of a library of 3-(aryl/heteroaryl thio)pyrazolo[1,5-a]pyrimidine derivatives with broad functionalities. The selectivity and scalability of the methodology have been also demonstrated. Moreover, the efficiency of this strategy for sulfenylation of pyrazoles, indole, imidazoheterocycles, and 4-hydroxy coumarin has been proven. The mechanistic investigation revealed the radical-based mechanism and formation of diaryl disulfide as a key intermediate for this cross-dehydrogenative coupling reaction.