Visible-Light-Mediated, Organophotocatalytic C-H Thiocyanation of Pyrazolo[1,5- a ]pyrimidines.

Herein, we report a metal-free, organophotoredox-catalyzed sustainable C-H thiocyanation of a biologically active class of N-heterocycles, pyrazolo[1,5- a ]pyrimidines, with potassium thiocyanate (KSCN) using 9-mesityl-10-methylacridinium perchlorate as the photocatalyst (PC) and molecular oxygen as the terminal oxidant under blue-light-emitting diode irradiation at room temperature. The developed catalytic protocol features mild reaction conditions, a broad substrate scope, a high yield of products, and a straightforward scalability. Mechanistic studies revealed a radical pathway involving reductive quenching of the PC by KSCN.