A solution of sodium bis(trimethylsilyl)amide in tetrahydrofuran (1M, 0.70 mL, 0.70 mmol) was added at −78° C. under nitrogen to a stirred solution of 1-methyl-3-bromo-5-pyrazolone from Step 1 (0.10 g, 0.565 mmol) in dry tetrahydrofuran (2 mL). After 10 min, nonafluorobutanesulfonyl fluoride (0.13 mL, 0.70 mmol) was added dropwise. The resulting gel was warmed to room temperature and stirred for 1 hour. The solution was diluted with water (10 mL) and extracted with ethyl acetate (2×10 mL). The extracts were dried (Na2SO4) and concentrated. Flash column chromatography on silica, eluting with 10% ethyl acetate-isohexane, gave 1-methyl-3-bromo-5-(nonafluorobutanesulfonyloxy)pyrazole (0.204 g, 79%) as a colourless oil.
