Diisopropylethylamine → Ethyl 3-(Trifluoromethyl)pyrazole-4-carboxylate

To a suspension of hydrazine hydrochloride (10 g, 147 mmol) in EtOH (500 mL), DIPEA (45.3 mL, 267 mmol) was added slowly at −20° C. and stirred for 10 mins. Then 2-[1-Ethoxy-meth-(E)-ylidene]-4,4,4-trifluoro-3-oxo-butyric acid ethyl ester (Preparation 135, 32 g, 133.33 mmol) was added to above solution and the resulting mixture was stirred at room temperature for 16 hours. The reaction mixture was concentrated under reduced pressure and residue was partitioned between EtOAc (200 mL) and water (50 mL). The organic layer was washed with water (25 mL), dried (Na2SO4) and evaporated in vacuo. The crude material was purified by column chromatography on silica gel (Hexane:EtOAc 90:10) to afford the title compound as off white solid in 43% yield, 13 g.