As part of ongoing research programme on bicyclic heterocycles [1] [2] [3] [4] we have elaborated a new approach to 1H-pyrazolo[4,3-e][1,2,4]triazine derivative 3 and its synthetic precursor 2 by reaction of oxime 5-acetyl-3-(methylsulfanyl)-1,2,4-triazine (1) with phenylhydrazine hydrochloride under different reaction conditions. Phenylhydrazone of 5-acetyl-3-(methylsulfanyl)-1,2,4-triazine 2 To a solution of the oxime 1 (184 mg, 1 mmol) and phenylhydrazine hydrochloride (288 mg, 2 mmol) in

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... anol (10 ml) 37% HCl (0.3 ml) was added. The mixture was heated at 40 o C for 9 hours and then the solvent was evaporated in vacuo. The solid was collected by filtration, washed with water and recrystallized from ethanol/water mixture (1:1) to give 2 in 27% yield. Melting point: 224 o C. 1 H-NMR (CDCl 3 ): δ= 2.30 (s, 3H); 2.69 (s, 3H); 6.99-7.08 (m, 1H); 7.23-7.28 (m, 2H); 7.32-7.41 (m, 2H); 8.05 (s, 1H, NH); 9.63 (s, 1H). IR (KBr, cm -1 ): 3240 (NH); 2980, 1600, 700. EI-MS (70eV, m/z): 259 (7) [M + ]; 147 (45); 129 (100); 112 (54); 70 (90). Elemental Analysis: Calculated for C 12 H 13 N 5 S: C 55.60%; H 5.02%; N 27.03%. Found: C 55.53%; H 5.09%; N 26.99%. 3-Methyl -5-(methylsulfanyl)-1-phenyl-1H-pyrazolo[4,3-e][1,2,4]triazine 3 To a solution of the oxime 1 (184 mg, 1 mmol) and phenylhydrazine hydrochloride (216 mg, 1.5 mmol) in ethanol (10 ml) was added 37% HCl (0.3 ml). The mixture was heated at reflux for 5 hours and then the Molbank 2004