Solvent-free synthesis of 3-carboxycoumarins

3-Carboxycoumarins, an important class of biologically active compounds, ar e synthesized in very high yield and in an energy efficient manner, without use of noxious reagents or volatile organic solvents, either by direct rea ction of the solid reagents, or in an aqueous slurry. Remarkably, even thou gh the first step in the reaction cascade is a condensation reaction, the r eaction proceeds rapidly as a stirred aqueous slurry without application of heat. A reason for this phenomenon is advanced and recycling of the aqueou s filtrate post product separation is described. Although the reaction is n ot 100% atom efficient (1 mole of acetone is evolved for each mole of couma rin produced) it is a significant improvement on previously described metho ds for the synthesis of such compounds.