A convenient one-pot, three-component reaction of aromatic aldehydes, 6-amino-1,3-dimethyluracil and active
methylene compounds in the presence of Zr(HSO4)4 as a heterogeneous catalyst, under solvent-free conditions brings a
very simple and highly efficient method for the preparation of pyrimido[4,5-b]quinolines, pyrimido[5',4':5,6]pyrido[2,3-
d]pyrimidines, indeno[2',1':5,6]pyrido[2,3-d]pyrimidines and a new class of pyrimidinedione derivatives in excellent
yields. This approach is general and provides several advantages such as simple reaction set-up, very mild reaction
conditions, high yields, recyclability of the catalyst and environmentally friendly benign.