[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([OH:8])=[CH:4][C:3]=1[C:9](=O)[CH:10]([CH3:12])[CH3:11].[N:14]([O-])=O.[Na+].O.O.[Sn](Cl)Cl.[OH-].[Na+]>O.Cl>[OH:8][C:5]1[CH:4]=[C:3]2[C:2](=[CH:7][CH:6]=1)[NH:1][N:14]=[C:9]2[CH:10]([CH3:12])[CH3:11]A solution of 900 mg (5.02 mmol) of 1-(2-amino-5-hydroxyphenyl)-2-methyl-1-propanone in 30 ml of half-conc. hydrochloric acid is treated slowly at −5° C. with a solution of 364 mg (5.27 mmol) of sodium nitrite in 15 ml of water and, after addition is complete, stirred at this temperature for 30 min. A solution of 2.266 g (10.04 mmol) of tin(II) chloride dihydrate in 15 ml of conc. hydrochloric acid is then added dropwise to the reaction mixture at −5° C. and the reaction is slowly warmed to room temperature. The mixture is neutralized using 45% strength sodium hydroxide solution, filtered off through kieselguhr, washed with ethyl acetate, and the organic phase is dried over sodium sulphate, concentrated in vacuo and dried. 370 mg (36%) of 5-hydroxy-3-isopropyl-1H-indazole are obtained.
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