[Synthesis]
Ethyl 2-carbamoylbenzofuran-3-ylcarbamate (114 mg, 0.460 mmol, 1.0 eq.) was heated to reflux for 1 h in 5% NaOH solution (3.7 mL, 4.60 mmol, 10.0 eq.) and EtOH (2.2 mL). Upon completion of the reaction, the mixture was cooled to room temperature and the product was precipitated by addition of 37% HCl solution. The solid was collected by filtration and washed sequentially with water and ether. The resulting benzofuro[3,2-d]pyrimidine-2,4(1H,3H)-dione (40 mg, 43% yield) could be used in the next step of the reaction without further purification. The product was characterized as follows: 1H-NMR (500 MHz, DMSO): δ 12.03 (s, 1H), 11.43 (s, 1H), 8.00 (d, 3JHH = 7.3 Hz, 1H), 7.75 (d, 3JHH = 8.5 Hz, 1H), 7.64 (t, 3JHH = 7.3 Hz, 1H), 7.45 (t, 3JHH = 7.3 Hz, 1H), 7.45 (t, 3JHH = 7.3 Hz). 3JHH = 7.3 Hz, 1H); 13C-NMR (100 MHz, DMSO): δ 155.5, 154.9, 151.3, 133.3, 130.6, 129.8, 123.9, 121.6, 117.6, 112.9. |