Visible light-induced recyclable g-C3N4 catalyzed thiocyanation of C(sp2)-H bonds in sustainable solvents

A metal-free photocatalytic strategy for the preparation of thiocyanated heterocycles from inexpensive NH4SCN has been developed using carbon nitride (g-C3N4) as a general heterogeneous catalyst in a green solvent under an air atmosphere and the irradiation of a blue LED. Various thiocyanated heterocycles including indolo[2,1-a]isoquinolin-6(5H)-ones, benzimidazo[2,1-a]isoquinolin-6(5H)-ones, thioflavones, azaspiro[4.5]trienones and imidazo[1,2-a]pyridines were successfully synthesized in good yields (up to 96%). Importantly, this metal-free and external-oxidant-free procedure employed dimethyl carbonate as a green medium, avoiding the traditional volatile organic solvents. Moreover, the recyclable g-C3N4 catalyst could be used at least 8 times without significant loss of activities.

Automated summary

A metal-free photocatalytic strategy using carbon nitride as a catalyst has been developed for the preparation of thiocyanated heterocycles from inexpensive NH4SCN. Various thiocyanated heterocycles were successfully synthesized in good yields under green conditions, and the recyclable catalyst showed no significant loss of activities after multiple uses.