Mild preparation of chromeno[2,3-d]pyrimidines catalyzed by Bronsted acidic ionic liquids under solvent-free and ambient conditions

Bronsted acidic ionic liquids, namely 2-pyrrolidonium hydrogensulfate, N-methyl-2-pyrrolidonium hydrogensulfate, N-methyl-2-pyrrolidonium dihydrogenphosphate, (4-sulfobutyl)tris(4-sulfophenyl)phosphonium hydrogensulfate, triphenyl(propyl-3-sulfonyl)phosphonium toluenesulfonate, l-prolinium sulfate, and l-prolinium nitrate, catalyzed efficient one-pot pseudo-four-component reaction of salicylaldehydes, malononitrile, and secondary amine for preparation of chromeno[2,3-d]pyrimidines under solvent-free conditions at room temperature. The catalysts show environmentally benign character and can be easily prepared, stored, and recovered without obvious significant loss of activity.