Electrochemical oxidative synthesis of 1,3,4-thiadiazoles from isothiocyanates and hydrazones

A 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-catalysed electrochemical synthesis of 2-amino-1,3,4-thiadiazoles from isothiocyanates and hydrazones is presented. This protocol is mild, practical, metal-free and exogenous oxidant-free, and features a broad substrate scope. Extensive mechanistic investigations revealed that the reaction proceeds via a tandem addition/chemoselective C-S coupling sequence, and it is the hydrogenated DDQ that is oxidized at the anode, not the intermediate thiosemicarbazides.