Water → 5-Chloro-2-(4-fluorophenyl)pyrazolo[1,5-a]pyridine

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To a solution of 2-(4-chloro-2-pyridinyl)-1-(4-fluorophenyl)ethanone oxime (8.0 g, 30 mmol) in 1,2-dimethoxyethane (50 mL) at 0° C. was added trifluoroacetic anhydride (6.3 g, 30 mmol), keeping the temperature below 10° C. during the addition. After the addition was complete, the reaction was warmed to room temperature. The solution was then cooled to 4° C. and a solution of triethylamine (8.4 mL, 60 mmol) in 1,2-dimethoxyethane (20 mL) was added over a period of 0.5 hours. The mixture was allowed to warm to room temperature and was stirred for 1.5 hours. To this mixture was added iron(II) chloride (40 mg) and the reaction was heated at 75° C. for 15 hours. The reaction mixture was poured into water (300 mL). The resulting suspension was extracted with ethyl acetate. The combined organics were dried (magnesium sulfate), filtered and concentrated to a solid residue. This residue was purified by flash chromatography (1:1 ethyl acetate-hexane) to give 5-chloro-2-(4-fluorophenyl)pyrazolo[1,5-α]pyridine (4.2 g, 57 %) as a white solid. 1H-NMR (CDCl3): δ 8.36 (d, 1H), 7.93 (q, 2H), 7.49 (d, 1H), 7.15 (t, 2H), 6.70 (dd, 1H), 6.69 (s, 1H); 19F-NMR (CDCl3): δ −113.30; MS m/z 247 (M+1).

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