N(OC(C)(C)C)=O.[CH2:8]([O:10][C:11]([C:13]1[CH:14]=[N:15][N:16]([C:19]2[CH:24]=[CH:23][C:22]([C:25]([F:28])([F:27])[F:26])=[CH:21][N:20]=2)[C:17]=1N)=[O:12])[CH3:9].[Cl:29]N1C(=O)CCC1=O>ClCCl>[CH2:8]([O:10][C:11]([C:13]1[CH:14]=[N:15][N:16]([C:19]2[CH:24]=[CH:23][C:22]([C:25]([F:28])([F:27])[F:26])=[CH:21][N:20]=2)[C:17]=1[Cl:29])=[O:12])[CH3:9]tert-Butyl nitrite (154 mg) was added slowly dropwise to a solution of 5-amino-1-[5-(trifluoromethyl)pyridin-2-yl]-1H-pyrazole-4-carboxylic acid ethyl ester (300 mg) and N-chlorosuccinimide (200 mg) in dichloromethane (10 ml) and stirred at room temperature for three hours. The reaction solution was concentrated while keeping not dried up, and the residue was purified with silica gel chromatography (ethyl acetate/n-hexane) to give 5-chloro-1-[5-(trifluoromethyl)pyridin-2-yl]-1H-pyrazole-4-carboxylic acid ethyl ester (140 mg) as a white solid.
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