Silica-bonded N-propyldiethylenetriamine sulfamic acid (SPDTSA) is employed as a recyclable heterogeneous solid acid catalyst for
the synthesis of benzopyrano[2,3-d]pyrimidines through one-pot condensation reaction of salicylaldehydes, malononitrile and secondary
amines at room temperature under solvent-free conditions. SPDTSA showed much the same efficiency when used in consecutive reaction
runs.