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

Abstract

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 (ZrOCl₂.8H₂O 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.

Graphical Abstract

Keywords:

• Deep eutectic solvents
• dihydropyridine derivatives
• Hantzsch pyridine synthesis
• multicomponent reaction

Acknowledgements

The authors gratefully acknowledge IIRBS, Mahatma Gandhi University, Kottayam for NMR analysis and UGC, India for financial support.

Additional information

Funding

This work was supported by University Grants Commission.