Sodium hydride (55% dispersion in mineral oil, 203 mg, 5 mmol) was added to an ice cooled solution of 5-(4-trifluoromethyl-phenyl)-1H-pyrazole-3-carboxylic acid ethyl ester (1 g, 4 mmol; PCT Int. Appl. (2003), WO 2004000785 A2) in DMF (60 ml) under an argon atmosphere. The solution was stirred for 10 min at 0° C. and for 40 min at ambient temperature. Trifluoroethyltriflate (1.07 g, 5 mmol) was added and the mixture was stirred for 3 h at ambient temperature. The solution was cooled to 0° C., 1 N HCl/ice water 1/2 and dichloromethane were added. The aqueous layer was extracted two times with dichloromethane, the combined extracts were washed with brine/ice water 1/1 and dried over sodium sulfate. Evaporation of the solvent under reduced pressure gave yellow crystals which were purified by column chromatography (silica gel, n-heptane/AcOEt) to yield 833 mg (2.27 mmol, 65%) of the title compound as colorless crystals.
