A series of pyrimido[4,5-d]pyrimidine derivatives were synthesized by a multicomponent reaction of urea/thiourea, aldehyde and barbituric or thiobarbituric acid in the presence of triethyl benzyl ammonium chloride as a catalyst under solvent-free conditions. The pure products were obtained after recrystallization from ethanol. All synthesized compounds were characterized using IR and NMR (1H and 13C) spectroscopic and elemental analyses data.
