64188-97-2

32315-10-9

21038-67-5

To a solution of 3-aminopyridine-4-carboxamide (5 g, 36.5 mmol) in tetrahydrofuran (THF, 100 mL) was sequentially added triphosgene (11.9 g, 40.1 mmol) and triethylamine (TEA, 7.4 g, 73 mmol). The reaction mixture was heated to reflux for 2 hours. After completion of the reaction, the solution was concentrated under reduced pressure and the residue was ground with an appropriate amount of water. The solid product was collected by filtration and washed sequentially with water and THF. The solid was dried to give pyrido[3,4-d]pyrimidine-2,4(1H,3H)-dione 4.1 g in 70% yield. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 11.62 (s, 1H), 11.58 (s, 1H), 8.66 (s, 1H), 8.40 (d, 1H, J = 5.2 Hz), 7.80 (d, 1H, J = 5.2 Hz).