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(Step 13) Synthesis of pyrrolo[2,1-f][1,2,4]triazine-2,4(1H,3H)-dione: [0342] 1-Amino-1H-pyrrole-2-carboxamide (14.00 g, 0.11 mol) and pyridine (9.90 mL, 0.12 mol) were suspended in anhydrous 1,4-dioxane (120 mL), followed by addition of ethyl chloroformate ( 11.70 mL, 0.12 mol). The reaction mixture was stirred under reflux conditions for 1 h and then concentrated under vacuum. The residue was continued to stir at 155 °C for 17 h. After cooling to room temperature, the mixture was diluted with methanol (50 mL). The resulting mixture was stirred at -15 °C for 2 h. The mixture was filtered, the solid product was collected and dried overnight at 60 °C through a vacuum desiccator to afford gray solid pyrrolo[2,1-f][1,2,4]triazine-2,4(1H,3H)-dione (12.70 g, 75% yield). Mass spectrum (ESI, cation mode) m/z: 152.2 [M + H]+; 1H NMR (400 MHz, DMSO-d6): δ (ppm) 12.96 (s, 1H), 11.7 (s, 1H), 7.13 (m, 1H), 6.75 (dd, J = 4.4, 1.6 Hz, 1H), 6.34 (dd, J = 4.3, 2.6 Hz, 1H).