Electrochemical Synthesis of 1,2,3-Thiadiazoles from α-Phenylhydrazones

We have developed an electrochemical approach for the synthesis of fully substituted 1,2,3-thiadiazoles from α-phenylhydrazones at room temperature, which is very challenging and complementary to the conventional thermal reactions. The key step involves anodic oxidation of phenylhydrazone derivatives at a constant current followed by N,S-heterocyclization. The protocol is remarkable in that it is free of a base and free of an external oxidant and can be converted to a gram scale for postsynthetic drug development with functional thiadiazoles. Most importantly, the electrochemical transformation reflected efficient electro-oxidation with an operationally friendly easy procedure with ample functional molecules. Cyclic voltammograms support the mechanism of this electro-oxidative cyclization process.