Electrochemical synthesis of tetrahydrobenzo[b]pyran derivatives in deep eutectic solvents

Abstract

• Synthesis of pyrans under electrochemical conditions in deep eutectic solvents. • Pyrans are formed in high yields, pure forms and under shorter reaction times. • The use of DES eliminated the need for supporting electrolyte. • The procedure described is highly efficient, catalyst-free and eco-friendly. The current work reported the first synthesis of 4 H -pyran derivatives via one pot reaction of dimedone, malononitrile and aromatic aldehydes under electrochemical (EC) synthesis conditions in deep eutectic solvents (DES). The effects of different experimental factors like; solvent, electrodes, supporting electrolytes, temperature and reaction time were studied to optimize the reaction conditions in order to maximize the products yield. The reaction proceeded completely using different substituted aldehydes except for hydroxybenzaldehydes where oxidation seems to hinder the formation of the target reaction product. Combining EC and DES afforded the pyran derivatives in high yields within short reaction times and in highly pure forms. Moreover, the use of DES eliminated the need for supporting electrolyte. The DES have been recycled two times without a significant loss in the catalytic activity. The procedure was highly efficient, catalyst-free and eco-friendly as evident from the calculations of the green chemistry metrics.