Synthesis
7.5 mmol (1.54 g) of 2,6-difluorophenylacetic acid was slowly added to 15 mL of concentrated nitric acid that had been pre-cooled to -10 °C over 20 min. After keeping the reaction mixture stirred at -10 °C for 15 min, it was carefully poured into an ice-water mixture to terminate the reaction. The reaction mixture was extracted with ether (4 x 10 mL). The organic phases were combined and sequentially washed with saturated saline (3 x 10 mL) and dried over anhydrous sodium sulfate. After concentration under reduced pressure to remove the solvent, the crude product was dissolved in ethanol (150 mL) and 5% palladium/carbon catalyst (150 mg) was added. The hydrogenation reaction was carried out overnight at room temperature at a hydrogen pressure of less than 30 psi. Upon completion of the reaction, the catalyst was removed by filtration through diatomaceous earth (Celite) and the filtrate was concentrated under reduced pressure to give the intermediate. The intermediate was treated with ethanol/concentrated hydrochloric acid (37% w/w, 10% v/v) solution with stirring for 10 min, followed by evaporation of the solvent under reduced pressure. The residue was treated with ethyl acetate to a gel, which was separated by filtration to give a solid product. The resulting solid was suspended in anhydrous methanol (4 mL) and sulfoxide chloride (0.2 mL) was slowly added dropwise. After the dropwise addition, the reaction mixture was heated to reflux overnight. After completion of the reaction, the solvent was removed under reduced pressure and the residue was neutralized with saturated sodium bicarbonate solution until no gas was produced, followed by extraction with ether (4 x 5 mL). The organic phases were combined, washed sequentially with water (3 x 5 mL) and dried over anhydrous sodium sulfate. Finally, concentration under reduced pressure afforded the target product methyl 2-(3-amino-2,6-difluorophenyl)acetate. Yield: 28%.1H-NMR (CDCl3, 200 MHz): δ = 6.86-6.71 (m, 2H, H-5 and H-6), 3.73 (s, 3H, OCH3), 3.71 (t, J = 1.3 Hz, 2H, H-7). Coupling between 1H and 19F was observed. Elemental analysis results: calculated values for C9H9F2NO2: C, 53.73; H, 4.51; N, 6.96. measured values: C, 53.68; H, 4.55; N, 6.89.
References
[1] Medicinal Chemistry Research, 2017, vol. 26, # 5, p. 975 - 986
