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 wi th propynoic and propenoic acids and ethyl acetoacetate using solid acid ca talysts and microwave irradiation produces coumarins in excellent yields. T he use of heterogeneous catalysts eliminates the production of acidic waste streams associated with conventional (Lewis) acid catalysts. This quick, e fficient and environmentally friendly procedure permits the synthesis of su bstituted coumarins as well as coumarins without 4-alkyl substituents, whic h are the most difficult to synthesize.