Phospho sulfonic acid: a versatile and efficient solid acid catalyst for facile synthesis of bis-(4-hydroxycoumarin-3-yl) methanes under solvent-free conditions

Biscoumarin derivatives are synthesized via a simple, one-pot, pseudo three-component reaction between various arylaldehydes and 4-hydroxycoumarin using phospho sulfonic acid as a reaction mediator under solvent-free neat conditions in good to excellent yields. High yields, short reaction time, easy work-up, elimination of solvents and environmentally benign milder reaction conditions are the advantages of this procedure.