Phospho sulfonic acid: a novel and efficient solid acid catalyst for the one-pot preparation of indazolo[1,2-b]-phthalazinetriones.

An efficient one-pot condensation of aldehyde, dimedone and phthal- hydrazide has been achieved in the presence of a catalytic amount of phospho sulfonic acid as a novel environmentally benign heterogeneous solid acid under solvent-free conditions. Diverse indazolo[1,2-b]phthalazinetrione derivatives were prepared in good to excellent yields in short times. The economical factors (time, cost, waste, etc.) for this three-component reaction hold promise for the future of organic synthesis. [ABSTRACT FROM AUTHOR]