Ammonium Chloride → Methyl 3-(2-amino-4-fluorophenylamino)-2-methylpropanoate

To a solution of methyl 3-(4-fluoro-2-nitrophenylamino)-2-methylpropanoate (14.0 g, 54.6 mmol) in ethanol (250 mL) were added zinc powder (14.2 g, 218 mmol) and saturated ammonium chloride (28.4 mL) at 0° C. Once addition was completed, the reaction mixture was stirred at reflux for 1 hour. Then the mixture was cooled to room temperature, filtered, and washed with ethanol (200 mL). The organic phase was concentrated in vacuo, dissolved in water (250 mL), and extracted with ethyl acetate (200 mL*3). The combined organic layers was separated, dried over anhydrous sodium sulfate, and concentrated to give a residue. The residue was purified by column chromatography (silica gel, petroleum ether/ethyl acetate=2:1) to afford methyl 3-(2-amino-4-fluorophenylamino)-2-methylpropanoate as a black solid (10.0 g, 81%).