Phosphorus oxychloride → Ethyl 6-chloro-2-(2,4-difluorophenyl)pyridine-3-carboxylate

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Reaction Conditions

Reaction Steps

To a nitrogen purged 500 mL, 3-necked flask, fitted with a reflux condenser, heating mantle and a thermocouple was charged 2-(2,4-difluorophenyl)-3-(ethoxycarbonyl)pyridine 1-oxide, 4 (21 g, 75 mmoles, 1.0 eq), followed by 150 mL dichloroethane. Phosphorous oxychloride (75 mL) was added in one aliquate with stirring, causing an immediate rise in temperature from 21 to 23° C. followed by gradual warming. The solution was heated under nitrogen to 70-75° C. (completeness of reaction determined by HPLC). The reaction was then cooled to room temperature and concentrated under vacuum to remove most of the POCl3. The remainder was quenched by slowly pouring onto 450 g of ice. The mixture (after the ice melted) was then extracted into methylene chloride (2×200 mL). The combined organics were dried (MgSO4), filtered through silica, eluted with methylene chloride, and concentrated to give the title Compound, 5, as an orange solid. 1H NMR (500.0 MHz, CDCl3) d 8.15 (d, J=8.2 Hz, 1H), 7.54 (td, J=8.5, 5.0 Hz, 1H), 7.34 (d, J=8.2 Hz, 1H), 6.96-6.92 (m, 1H), 6.79-6.74 (m, 1H), 4.16 (q, J=7.2 Hz, 2H), 1.10 (t, J=7.1 Hz, H) ppm.

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