[NH2:1][C:2]1[C:6]2=[N:7][C:8]([CH3:12])=[CH:9][C:10]([Cl:11])=[C:5]2[NH:4][N:3]=1.[N:13]([O-])=O.[Na+].C(=O)([O-])[O-].[Na+].[Na+]>O.S(=O)(=O)(O)O>[Cl:11][C:10]1[CH:9]=[C:8]([CH3:12])[N:7]=[C:6]2[C:2](=[N+:1]=[N-:13])[N:3]=[N:4][C:5]=12A solution of 3-amino-7-chloro-5-methyl-1H-pyrazolo[4,3-b]pyridine (D7) (0.5 g) in water (13.5 ml) and concentrated sulphuric acid (2 ml) was treated at 0° with a solution of sodium nitrite (0.406 g) in water (2 ml) added dropwise with stirring. On completion of the addition the mixture was stirred at 0° for 20 min before bringing to pH 8 with saturated sodium carbonate. The resulting solid was collected and dried (0.18 g). The filtrate was extracted with chloroform (3×50 ml), the combined extracts dried with magnesium sulphate, filtered and evaporated to dryness to give a yellow solid which was combined with the solid originally collected, m.p. 119°-124° (combined yield 0.5 g). This crude material was recrystallised from cyclohexane to give the title compound as yellow needles (0.358 g, 68%), m.p. 123.5°-125° (decomposition). (Found: C, 43.51; H, 1.88; N, 35.79; Cl, 18.68. C7H4ClN5 requires C, 43.43; H, 2.08; N, 36.17; Cl, 18.31%). Found M+ 193.0154, C7H4ClN5 requires 193.0155.
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