Metal-free electrochemical C4-H arylation of 5-aminopyrazoles with gentisate derivatives.

We report a metal-free electrochemical C4-H arylation of 5-aminopyrazoles with readily available gentisate derivatives under constant current at room temperature, without the need for bases, chemical oxidants, or transition-metal catalysts. A variety of 1,3,4-trisubstituted pyrazoles bearing a free 5-amino group were obtained in good to excellent yields with complete C4 regioselectivity. The use of gentisate esters as arylating agents circumvents the need for preoxidation to quinones, streamlining the synthetic sequence. Mechanistic studies support a radical-radical cross-coupling pathway involving proton transfer, electron transfer, and cathode reduction. This protocol offers a practical and sustainable approach to synthesize functionalized pyrazoles, which are privileged scaffolds in pharmaceuticals and agrochemicals.