[Cl:1][C:2]1[CH:3]=[C:4]([C:7]2[CH:11]=[CH:10][NH:9][N:8]=2)[S:5][CH:6]=1.[I:12]N1C(=O)CCC1=O.S([O-])([O-])(=O)=S.[Na+].[Na+].C(=O)([O-])[O-].[Na+].[Na+]>CN(C)C=O>[Cl:1][C:2]1[CH:3]=[C:4]([C:7]2[C:11]([I:12])=[CH:10][NH:9][N:8]=2)[S:5][CH:6]=1
3-(4-chloro-2-thienyl)-1H-pyrazole (24.0 mmol) was dissolved in 50 mL N,N-dimethylformamide under argon atmosphere. N-Iodosuccinimide (25.1 mmol) was added in small portions. The reaction mixture was stirred at room temperature overnight. 5% aqueous sodium thiosulfate solution and saturated aqueous sodium carbonate solution were added and the mixture was stirred at room temperature for 1 h. The white precipitate was filtered, washed thoroughly with water and dried in vacuum to afford 6.80 g of 3-(4-chloro-2-thienyl)-4-iodo-1H-pyrazole (91% yield) that was used without further purification.
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