Rapid Synthesis of Novel and Known Coumarin-3-carboxylic Acids Using Stannous Chloride Dihydrate under Solvent-Free Conditions

Various coumarin-3-carboxylic acid (= 2-oxo-2H-1-benzopyran-3-carboxylic acid; CcaH) derivatives have been synthesized in good yields using catalytic amounts of SnCl2 center dot 2 H2O under solvent-free conditions. This inexpensive, nontoxic, and readily available catalytic system (10 mol-%) efficiently catalyzes the Knoevenagel condensation and intramolecular cyclization of various 2-hydroxybenzaldehydes or acetophenones with Meldrum's acid. High product yields, use of inexpensive and safe catalyst, and solvent-free conditions display both economic and environmental advantages.