Synthesis of 1,3-dimethyl-2,4-dioxo-1H,2H,3H,4H-quinazolines and 1,5-dihydro-1,3-dimethyl-5-nitromethyl-2H- pyrano[4,3-d]pyrimidine-2,4(3H)-diones

5,7-Diaryl-1,3-dimethyl-2,4-dioxo-1H,2H,3H,4H-pyrano[4,3-d]pyrimidinium bromides react with malonodinitrile to form 1,3-dimethyl- 2,4-dioxo-1H,2H,3H,4H-quinazolines, whereas their reaction with nitromethane gives dihydro-1,3-dimethyl-5-nitromethyl-2H- pyrano[4,3-d]pyrimidine-2,4(3H)-diones, the structure of one of them was established by X-ray analysis.