Effective preparation of hexahydroquinolines under ambient and solvent-free conditions

The mild acidic ionic liquids such as N-methyl-2-pyrrolidonium dihydrogen phosphate [NMP][H2PO4], N-methyl-2-pyrrolidonium hydrogen sulfate [NMP][HSO4], Triethylamine hydrogen sulfate [Et3N-H][HSO4], l-prolinium sulfate [l-Pro2][SO4] and l-prolinium nitrate [l-Pro][NO3] were used as efficient catalysts for the one-pot four-component condensations of aromatic aldehydes, dimedone, ethyl acetoacetate, and ammonium acetate under solvent-free conditions. Some derivatives of ethyl 4-(aryl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate were obtained under solvent-free conditions in high yields. Simple reaction, mild condition and easy work-up procedures are advantages of the present work. Also, the ionic liquids can be recycled several times without significant loss of their activity.