Water → 3-Cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-pentafluoropropanoylpyrazole

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To a stirred solution of 3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)-4-iodopyrazole (3.0 g) in tetrahydrofuran (80 ml) at -80° C. under an atmosphere of nitrogen was added, at such a rate that the temperature of the reaction mixture did not exceed -73° C., n-butyllithium (2.78 ml of a 2.5M solution in hexanes). The mixture was stirred at -73° C. for 10 minutes and then a solution of methyl pentafluoropropionate (0.89 ml) in tetrahydrofuran (5 ml) was then added at such a rate that the temperature of the reaction mixture did not exceed -75° C. Upon completion of the addition the mixture allowed to warm to room temperature over a period of 1.5 hours. Water (100 ml) was added and the mixture extracted twice with ethyl acetate (80 ml). The combined organic layers were dried (Na2SO4) and evaporated to give a pale yellow solid which was purified by column chromatography on silica gel (150 g) eluted with dichloromethane:hexane (9:1). Combination and evaporation of suitable fractions gave a yellow oil which was further purified by column chromatography on silica gel (50 g) eluted with dichloromethane:hexane (9:1). Combination and evaporation of suitable fractions gave the title compound as a white solid, m.p. 120° C.

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