Trifluoroacetic acid → (6-Methoxy-2-oxo-benzooxazol-3-yl)-acetic acid ethyl ester

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A solution of 6-methoxy-2-benzoxazolinone (0.78 g, 4.72 mmol) dissolved in 5 mL of anhydrous THF was added to a suspension of sodium hydride (0.208 g of a 60% dispersion in mineral oil, 5.2 mmol) in 10 mL of anhydrous THF at room temperature and stirred for 10 minutes. Then, ethyl bromoacetate (0.629 mL, 5.67 mmol) was added and stirred at room temperature for two hours. HPLC (Eclipse XDB-C18, 4.6×250 mm, 5 micron, 1-99% CH3CN/H2O with 0.1% trifluoroacetic acid) showed that almost all of the starting material (Rt=4.36 min) was gone and that a new peak (Rt=6.0 min) had formed. The reaction was quenched with 2 mL of 4.0M HCl in dioxane. The solvent was removed by rotary evaporation and the residue was adsorbed onto approximately 10 g of silica gel and purified by column chromatography (40 g silica gel 40 um, gradient elution from 100% dichloromethane to 35% methanol/65% dichloromethane over 40 minutes) to give ethyl[6-(methyloxy)-2-oxo-1,3-benzoxazol-3(2H)-yl]acetate (0.96 g, 3.84 mmol, 81%) as a white crystalline solid. MS (ES) m/e 252 [M+H]+.

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