Acetic Anhydride → [3-(Acetyloxy)phenyl]acetic acid

Temperatur

40 °C

A stirred suspension of 3-hydroxyphenylacetic acid (10.2 g, 67 mmol) in acetic anhydride (100 mL, 1.06 mol) under anhydrous conditions was treated with pyridine (0.5 mL). In the mildly exothermic reaction, the solids dissolved within several minutes and the mixture was maintained at 40° C. for 5 h. The reaction was concentrated in vacuo to about half volume, then water (30 g) in the form of ice chips was added at such a rate that the temperature remained <45° C. When the exotherm had subsided, a second portion of water (200 mL) was added slowly and the mixture was stirred for another 30 min. The precipitated solid was filtered, washed with water and dried to constant weight in vacuo over P2O5 to give 3-acetoxyphenylacetic acid (11.7 g, 90%) which was used without further purification. In an inert atmosphere, a solution of the above 3-acetoxyphenylacetic acid (1.942 g, 10 mmol), diphenylphosphoryl azide (2.8 g, 10.17 mmol) and diisopropylethylamine (1.92 mL, 11 mmol) in benzene (25 mL) was stirred at room temperature for 1 h, then the reaction temperature was slowly raised to 70° C. Evolution of gas began to be evident as the reaction temperature reached approximately 55° C. and became much more vigorous as the reaction temperature approached 70° C. Within 30 minutes at that temperature gas evolution had stopped and the reaction solution containing 3-acetoxybenzylisocyanate was cooled to 40° C. Another portion of DIPEA (3.84 mL, 22 mmol) was added, followed by 4-amino-2-chlorobenzoic acid methyl ester hydrochloride salt (2.95 g, 13.3 mmol) and the brownish purple solution was stirred and heated at reflux under argon overnight. The reaction mixture was cooled, diluted with benzene (50 mL) and washed in turn with 1N HCl (50 mL) and dilute brine. The aqueous layers were re-extracted with benzene, and the combined extracts were dried (MgSO4), evaporated, and purified by HPLC (silica gel; 40% ethyl acetate/hexane). Evaporation of the appropriate fractions provided 3.24 g of the solid urea which was then crystallized from dichloromethane-ethyl acetate to give 4-[[[[(3-acetoxy)phenyl]methyl]amino]-carbonyl]amino-2-chlorobenzoic acid, methyl ester (2.71 g, 72%) as a colorless solid, mp 113-114° C.