Dual solvent-catalyst role of deep eutectic solvents in Hantzsch dihydropyridine synthesis

Deep eutectic solvents are a class of new generation green solvents formed from two or more components, which furnish a new homogeneous liquid phase with lower melting point than the individual components. Here, for the first time, dual role of DES as catalyst and reaction medium was studied for the synthesis of symmetric dihydropyridine derivatives from aldehyde, ethyl acetoacetate and ammonium acetate. The present article reports the suitability of six DESs for Hantzsch dihydropyridine synthesis at room temperature. Among this, DES 2 (ZrOCl2.8H(2)O and ethylene glycol at 1:2 ratio) was found to be the catalyst of choice with excellent recyclability. The role of DES in the present protocol was to activate the reactants through strong hydrogen bonding interaction and provide suitable medium for the reaction. The major advantages of DESs for the titled reaction are the easy preparation, low cost, non-volatility, biodegradability, simple catalytic process, excellent conversion and the reusability.

Automated summary

Deep eutectic solvents, formed from two or more components, demonstrate dual roles as catalyst and reaction medium for the synthesis of dihydropyridine derivatives. Among six DESs studied, DES 2 (ZrOCl2.8H(2)O and ethylene glycol at 1:2 ratio) was found to be the most effective catalyst with excellent recyclability. The major advantages of DESs in this reaction include easy preparation, low cost, non-volatility, biodegradability, simple catalytic process, excellent conversion, and reusability.