Unexpected formation of hexahydroxanthenediones by electrochemical synthesis in deep eutectic solvents

The current study reports the unexpected formation of xanthene-1,8-diones upon attempt to perform Biginelli reaction by reacting cyclohexanedione, thiourea and different aldehydes under electrochemical conditions in either ethanol or deep eutectic solvents and utilizing Amberlyst-15® as a heterogeneous acidic catalyst. The Biginelli reaction product; hexahydroquinazoline-5-one, was not observed even upon using varying amounts of catalysts, different reaction times, different types of electrodes, and different types of substituted benzaldehydes. The mechanism of formation of xanthene-1,8-dione was followed up by cyclic voltammetry.