t-BuOK (0.47 mL, 1.0 M in THF) was added to propan-2-one oxime (35 mg, 0.47 mmol). After stirring for 30 minutes, THF (0.5 mL) was added, and the reaction mixture was cooled to −78° C. A solution of 5-acetyl-2-(2-chlorophenylamino)-3,4-difluorobenzoic acid methyl ester (6) (50.0 mg, 0.147 mmol) in THF (1 mL) was added. The reaction mixture was slowly warmed to 0° C. and stirred for 2 hours. The reaction mixture was quenched with saturated aqueous NH4Cl, diluted with EtOAc and water. The aqueous layer was separated and extracted with EtOAc. The combined organic extracts were dried over MgSO4, filtered, and concentrated in vacuo to give the 5-acetyl-2-(2-chlorophenylamino)-3-fluoro-4-isopropylideneaminooxybenzoic acid methyl ester. The recovered oxime was suspended in a 1:1 mixture of 5% aqueous HCl and MeOH (30 ml) and heated to reflux. After 1 hour, the reaction mixture was cooled to room temperature and diluted with EtOAc. The organic layer was washed with water, dried (MgSO4) and concentrated. Purification by flash column chromatography using the Biotage system (40% methylene chloride in hexanes) provided 17 mg (35% for two steps) of the desired product (7).
