Use of microwave irradiation and solid acid catalysts in an enhanced and environmentally friendly synthesis of coumarin derivatives

Condensation of phenol, 1,3-dihydroxybenzene and 1,3,5-trihydroxybenzene with propynoic and propenoic acids and ethyl acetoacetate using solid acid catalysts and microwave irradiation produces coumarins in excellent yields. The use of heterogeneous catalysts eliminates the production of acidic waste streams associated with conventional (Lewis) acid catalysts. This quick, efficient and environmentally friendly procedure permits the synthesis of substituted coumarins as well as coumarins without 4-alkyl substituents, which are the most difficult to synthesize.