A convenient synthesis of coumarin-3-carboxylic acids via Knoevenagel condensation of Meldrumʹs acid with ortho-hydroxyaryl aldehydes or ketones

Coumarin-3-carboxylic acids were obtained in high yields with excellent purity from ortho-hydroxybenzaldehydes and Meldrumʹs acid after a 2 h reflux in ethanol. The less reactive ketones were first reacted with alcoholic ammonia to form ketimines, which were then condensed with Meldrumʹs acid to generate 4-alkylcoumarin-3-carboxylic acids in moderate yields.