Methyl chloroformate → 2-(3,4-difluorophenyl)oxazol-5(4H)-one

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To a solution of 2-(3,4-difluorobenzamido)acetic acid (5.18 g, 24.1 mmol) in THF (25 mL) in a 100 mL round-bottomed flask was added 4-methylmorpholine (2.44 g, 24.1 mmol) to give a colorless solution. The solution was cooled to −10° C. and methyl chloroformate (2.28 g, 24.1 mmol) was added slowly over the course of thirty minutes while maintaining the solution at −10° C. A white precipitate started to form almost immediately and the solution became increasingly orange in color. Once the addition of chloroformate was complete the solution was stirred at −10° C. for 1 hour and warmed to room temperature over the course of an hour. The solution was filtered through a glass frit and the remaining solid was washed thoroughly with THF until colorless. The combined filtrate was evaporated under reduced pressure to provide 2-(3,4-difluoro-phenyl)oxazol-5(4H)-one as a light orange solid (4.5 g, 95%). LCMS (+ESI) m/z 198.2 [M+H]+. 1H-NMR (CDCl3) δ 7.85 (m, 1H), 7.78 (m, 1H), 7.30 (m, 1H), 4.45 (s, 2H).

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