Phosphorus oxychloride → 4-chloro-2-(2,6-dichlorophenyl)-2H-pyrazolo[4,3-c]pyridine

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2-(2,6-Dichlorophenyl)-2H-pyrazolo[4,3-c]pyridine 5-oxide (1.12 g, 4 mmol) was slowly added to phosphorous oxychloride (8 mL). Tetrabutylammonium chloride (1.11 g, 4 mmol) was then added. The reaction mixture was heated at 80° C. for 5 hours and then cooled to room temperature. The reaction was poured into a mixture of ethyl acetate and sodium hydrogen carbonate (sat. aq.) and the layers were partitioned. The organic layer was washed with sodium hydrogen carbonate (sat. aq.) and brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The resultant residue was purified by silica gel flash chromatography (20% ethyl acetate in cyclohexane) to afford the title compound as a white solid (590 mg, 49% yield). 1H NMR (400 MHz, DMSO-d6): δ 9.33 (d, J=1.0 Hz, 1H), 8.11 (d, J=6.0 Hz, 1H), 7.83 (d, J=1.3 Hz, 1H), 7.82-7.81 (m, 1H), 7.75-7.71 (m, 1H). LCMS (Method D): RT=3.42 min, m/z: 298 [M+H+].

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