[NH2:1][C:2]1[C:7]([Cl:8])=[CH:6][C:5]([Br:9])=[CH:4][C:3]=1[C:10](=O)[CH3:11].OS(O)(=O)=O.[N:18]([O-])=O.[Na+].O.O.Cl[Sn]Cl>O>[Br:9][C:5]1[CH:4]=[C:3]2[C:2](=[C:7]([Cl:8])[CH:6]=1)[NH:1][N:18]=[C:10]2[CH3:11]
To a 0° C. solution of 1-(2-amino-5-bromo-3-chlorophenyl)ethanone (206 mg, 0.83 mmol) in 50% aqueous solution of concentrated H2SO4 was slowly added NaNO2 (73 mg, 1.0 mmol). The cooling bath was removed following the addition of NaNO2, stirred at room temperature for 1 hour and then recooled to 0° C. before addition of SnCl2.2H2O (573 mg, 2.49 mmol). The mixture was stirred at 0° C. for 1 hour before dilution with water. The solids were collected by vacuum filtration to afford 5-bromo-7-chloro-3-methyl-1H-indazole (130 mg, 64%).
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