[Cl:1][C:2]1[S:6][C:5]([C:7]2[CH:11]=[C:10]([CH3:12])[NH:9][N:8]=2)=[CH:4][CH:3]=1.[Br:13]N1C(=O)CCC1=O.S([O-])([O-])(=O)=S.[Na+].[Na+].C(=O)([O-])[O-].[Na+].[Na+]>>[Br:13][C:11]1[C:7]([C:5]2[S:6][C:2]([Cl:1])=[CH:3][CH:4]=2)=[N:8][NH:9][C:10]=1[CH3:12]3-(5-chloro-2-thienyl)-5-methyl-1H-pyrazole (111 mmol) was dissolved in 200 mL dry 1V, N-dim ethyl formamide and cooled to 0° C. under nitrogen atmosphere. N-Bromosuccinimide (118 mmol) was added in small portions at 0° C. The reaction mixture was allowed to warm to room temperature and was stirred overnight. The solution was poured into a mixture of saturated aqueous sodium thiosulfate solution and saturated aqueous sodium carbonate solution (1:1) at room temperature. The precipitate was filtered, washed thoroughly with water, dissolved in ethyl acetate, dried over MgSO4, filtered and evaporated to afford 19.5 g of 4-bromo-3-(5-chloro-2-thienyl)-5-methyl-1H-pyrazole (64% yield) that was used without further purification.
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