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 per-form Biginelli reaction by reacting cyclohexanedione, thiourea and different aldehydes under electrochemical conditions in either ethanol or deep eutectic solvents and utilizing Amberlyst-15 & REG; 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, dif-ferent types of electrodes, and different types of substituted benzaldehydes. The mechanism of formation of xanthene-1,8-dione was followed up by cyclic voltammetry.

Automated summary

This study reports the unexpected formation of xanthene-1,8-diones during the attempted Biginelli reaction. The reaction was carried out using cyclohexanedione, thiourea, and different aldehydes under electrochemical conditions with ethanol or deep eutectic solvents, and Amberlyst-15 & REG; was used as a catalyst. The formation of the expected Biginelli reaction product, hexahydroquinazoline-5-one, was not observed under various reaction conditions, suggesting a different mechanistic pathway leading to xanthene-1,8-dione formation. The mechanism was elucidated through cyclic voltammetry.