Regioselective C‐H Thio‐ and Selenocyanation of Pyrazolo[1,5‐<i>a</i>]pyrimidines

Herein, we report a metal-free, N-chlorosuccinamide (NCS)-mediated, highly efficient, and regioselective C-H thio- and selenocyanation of pyrazolo[1,5-a]pyrimidines using KSCN and KSeCN respectively. The transformation required only NCS (1 equiv) and operated under mild conditions such as ambient temperature and aerobic atmosphere. This method was found to be highly efficient for the C-H thiocyanation of pyrazolo[1,5-a]pyrimidines as compared to our previously developed photocatalytic strategy and also enabled the C-H selenocyanation of the substrates to access 3-selenocyanatopyrazolo[1,5-a]pyrimidines, for the first time, which was unexplored or unsuccessful so far. A wide variety of new pyrazolo[1,5-a]pyrimidines bearing -SCN or -SeCN functional groups were synthesized in good to excellent yield. The developed protocol features a broad substrate scope, high functional group tolerance, mild conditions, high to excellent yield of products, efficient scalability, and synthetic diversifications of products. Mechanistic studies revealed an ionic pathway for this reaction.