[Cl:1][C:2]1[CH:3]=[C:4]([CH:18]=[CH:19][C:20]=1[Cl:21])[CH2:5][N:6]1[C:14]2[C:9](=[CH:10][C:11]([O:15]C)=[CH:12][CH:13]=2)[C:8]([OH:17])=[N:7]1.Br.O.[OH-].[Na+]>C(O)(=O)C>[Cl:1][C:2]1[CH:3]=[C:4]([CH:18]=[CH:19][C:20]=1[Cl:21])[CH2:5][N:6]1[C:14]2[C:9](=[CH:10][C:11]([OH:15])=[CH:12][CH:13]=2)[C:8]([OH:17])=[N:7]14.85 g 1-(3,4-dichlorobenzyl)-5-methoxy-1H-indazole-3-ol are heated in 30 ml acetic acid and 30 ml 50% hydrobromic acid for 4 hours under gentle reflux. After cooling, the mixture is stirred into 250 ml water, rendered alkaline with concentrated sodium hydroxide solution and extracted twice with 80 ml tert-butyl methyl ether. The aqueous phase is acidified with sulfuric acid and extracted by shaking three times with 200 ml tert-butyl methyl ether. The combined ether phases are dried over sodium sulfate and distilled to dryness under vacuum. The residue is washed with a small amount of tert-butyl methyl ether and dried.
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