The synthesis of coumarin-3-carboxylic acids and 3-acetyl-coumarin derivatives using heteropolyacids as heterogeneous and recyclable catalysts

Coumarin-3-carboxylic acids and 3-acetyl-coumarins were obtained in high yields with excellent purity from ortho-hydroxybenzaldehydes and 1-ethylacetoacetate or malonic acid after a 2 h reflux in ethanol in the presence of a catalytic amount of different heteropolyacids (HPAs). The less reactive 1-(2-hydroxy-phenyl)-ethanone was first reacted with alcoholic ammonia to form ketimines, which were then condensed with 1-ethylacetoacetate or malonic acid to generate 4-methyl coumarin-3-carboxylic acids and 4-methyl 3-acetyl-coumarins in moderate yields.