Ultrasound-mediated synthesis of 4-substituted 1,4-dihydropyridine-3,5-dicarboxylates catalyzed by 1-carboxymethyl-3-methylimidazolium tetrafluoroborate under solvent free condition

• Brønsted acid ionic liquid [CMMIM]BF4 was used as catalyst.
• Ultrasound-assisted preparation of 1,4-dihydropiridine was finished under solvent free condition.
• The procedure showed high yields, exclusive selectivity, short reaction times, and mild conditions.
• The catalyst could be recycled and reused.

4-Substituted 1,4-dihydropyridine-3,5-dicarboxylates (4) have been synthesized by the solvent-free reaction of aldehyde, methyl propiolate and ammonium carbonate catalyzed by ionic liquid 1-carboxymethyl-3-methylimidazolium tetrafluoroborate under ultrasonic irradiation. The effects of changes in the ultrasonic power, temperature, catalysts and reactants on the synthesis of 4-substituted 1,4-dihydropyridine-3,5-dicarboxylates (4) are discussed. With the optimized reaction conditions, various aldehydes were used to synthesize 1,4-dihydropyridines (4) under the influence of ultrasound irradiation. Compared with the conventional thermal methods, the remarkable advantages of this method are the simple experimental procedure, shorter reaction time (2–10 min) and high yield of product (76–95%). Furthermore, the green catalytic system can be recycled specific times without significantly decreasing the yields and reaction rates.