Three-component coupling reactions in ionic liquids: An improved protocol for the synthesis of 1,4-dihydropyridines

Three-component condensation of aldehyde, beta-ketoester and methyl 3-aminocrotonate proceeds smoothly in 1-n-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF4 or 1-n-butyl-3-methylimidazolium hexafluorophosphate [bmim]PF6 ionic liquids at room temperature under mild conditions to afford the corresponding 1,4-dihydropyridine derivatives in high yields. The recovered activated ionic liquids are recycled for four to five runs with no loss in activity.