To a solution of ethyl 3-methyl-1-(2,4,6-trichlorophenyl)-1H-pyrazole-5-carboxylate (500 mg, 1.50 mmol) in trifluoroacetic acid (2.54 ml) was added trifluoroacetic anhydride (1.48 ml) followed by an addition of ammonium nitrate (240 mg, 3.00 mmol). The mixture was stirred for 20 h at room temperature and neutralized with aqueous potassium carbonate. The aqueous solution was extracted with ethyl acetate. The extract was dried over magnesium sulfate and concentrated under vacuum. The residue was purified by silica gel chromatography eluting with 3% ethyl acetate/n-hexane to give the title compound (372 mg, 66%).
