To a solution of [4-(4-Amino-phenyl)-6-chloro-3-methyl-naphthalen-2-yl]-acetic acid methyl ester (115 mg, 0.34 mmol) and acetic anhydride (68.8 mg, 67 mmol) were mixed together under nitrogen and then pyridine (3 mL) was added to afford clear solution which was stirred for 10 minutes. The mixture was diluted with ethyl acetate (20 mL) and washed with 1.0 N HCl solution (10 mL), brine solution (20 mL) and dried over anhydrous magnesium sulfate. Filtration of the drying agent and concentration of the solvent under vacuum gave [4-(4-acetylamino-phenyl)-6-chloro-3-methyl-naphthalen-2-yl]-acetic acid methyl ester (120 mg, 93.1%) as a white solid. 1H NMR (300 MHz, DMSO-d6) δ ppm 10.13 (s, 1 H), 7.94 (d, J=8.8 Hz, 1 H), 7.86 (s, 1 H), 7.76 (d, J=8.2 Hz, 2 H), 7.46 (dd, J=8.8, 1.8 Hz, 1 H), 7.11-7.19 (m, 3 H), 3.95 (s, 2 H), 3.65 (s, 3 H), 2.10 (s, 3 H), 2.07 (s, 3 H). HRMS calcd. for C22H19ClNO3 [(M−H)−.
