1. Dissolve isoxazole (35.0 g, 506.0 mmol) in ethanol (200 mL) at 0°C and slowly add sodium ethoxide (197 mL, 21% ethanol solution, 532 mmol) while stirring. After the addition was completed, the reaction mixture continued to be stirred for 30 minutes.
2. The solvent was removed by vacuum and water (200 mL) was added to neutralize the reaction mixture. Subsequently, aminourea hydrochloride (56.43 g, 506 mmol) was added and stirred at 25 °C for 16 hours.
3. The reaction mixture was neutralized with NaOH (1N) to pH~7 and then extracted with chloroform (5*). The organic layer was dried over Na2SO4, filtered and concentrated. Purification by chromatography using a hexane-EtOAc gradient elution afforded 5-amino-1H-pyrazole-1-carboxamide as a white solid (13.8 g, 21.6%).TLC Rf = 0.51 (1:1 EtOAc:hexane).
4. a solution of 5-amino-1H-pyrazole-1-carboxamide with triethyl orthoformate was heated at 110 °C for 15 hours. After completion of the reaction, the reaction mixture was concentrated to dryness and ground.
5. The resulting solid was dried in vacuum to afford pyrazolo[1,5-a][1,3,5]triazin-4(3H)-one (8.23 g, 76.6%) as a brown solid. lCMS (m/z): m + H = 137.1; tR = 0.22 min; TLC Rf = 0.44 (9:1 DCM:MeOH).
![4-oxo-3H-pyrazolo[1,5-a]1,3,5-triazine](/CAS/GIF/54346-27-9.gif)