Microwave-assisted synthesis of coumarin-3-carboxylic acids under ytterbium triflate catalysis

Coumarin-3-carboxylic acids represent a class of natural occurring and semi-synthetic products with valuable reported pharmacological activities. In this Letter a new and improved method for the chemical synthesis of the title compounds is described. Coumarin-3-carboxylic acids have been synthesized in good to excellent yields under microwave irradiation and solvent-free conditions from differently substituted 2-hydroxybenzaldehydes or 2 hydroxyacetophenones and Meldrum’s acid as starting materials in the presence of Yb(OTf)3 hydrate 5% mol as the catalyst.