Multicomponent Synthesis of Chalcogenated Pyrazoles under Visible-Light

Pyrazole derivatives are valuable heterocycles with applications in medicinal chemistry, materials science, and catalysis. Herein, we report a mild, metal-free, visible-light-driven multicomponent protocol for the synthesis of an class of chalcogenated pyrazoles. Reaction conditions were optimized by evaluating the light source, irradiation power, photocatalyst, additives, reaction time, temperature, solvent, iodine source, and catalyst loading. The optimal conditions employed catalytic iodine under blue LED irradiation (50 W) for 12 h in ethyl acetate, without additives or photocatalysts. The methodology exhibited a broad substrate scope, accommodating diverse diselenides, disulfides, and hydrazines to afford more than 30 sulfur- and selenium-containing pyrazole derivatives in good to excellent yields. Synthetic utility was demonstrated through Clauson-Kaas derivatization of the products. This operationally simple protocol provides an efficient and sustainable platform for accessing structurally diverse chalcogenated pyrazoles under unified reaction conditions.