Amberlyst A-21®: An efficient, cost-effective and recyclable catalyst for the synthesis of substituted 4H-chromenes

A variety of substituted 4H-chromene derivatives have been synthesized in good to excellent yields from o-hydroxybenzaldehydes and ethyl cyanoacetate or malononitrile in ethanol using inexpensive and reusable catalyst i.e., Amberlyst A-21® under mild reaction conditions. The recovered activated catalyst is recycled in five times subsequent runs with no decrease in activity. The use of reusable catalyst makes this procedure quite simple, more convenient, economically viable and environmentally friendly.