A solution of N-(4-bromo-2-fluoro-benzyl)-2-hydroxy-5-nitro-benzamide (0.95 g, 2.6 mmol) in acetone (15 mL, 0.2 M) was treated with aq K2CO3 (2 M, 1.9 mL, 3.8 mmol) and t-butyl bromoacetate (2.2 mL, 8.4 mmol). After heating to 50° C. for 30 h, the reaction was acidified to pH 1-2 with 2 N HCl and extracted with ethyl acetate (3×). The combined organic extracts were washed with saturated aq NaCl, dried over Na2SO4, filter ed and concentrated. The crude oil was crystallized from heptane and ethyl acetate to give [2-(4-bromo-2-fluoro-benzylcarbamoyl)-4-nitro-phenoxy]-acetic acid tert-butyl ester as a white crystalline solid (1.21 g, 97%): 1H NMR (DMSO-d6, 300 MHz) δ 9.01 (br t, J=5.7 Hz, 1H), 8.58 (d, J=3.0 Hz, 1H), 8.33 ( dd, J1=9.0 Hz, J2=3.0 Hz, 1H), 7.51 (br d, J=9.6 Hz, 1H), 7.42-7.34 (m, 2H), 7.32 (d, J=9.3 Hz, 1H), 4.99 (s, 2H), 4.52 (d, J=5.7 Hz, 2H), 1.40 (s, 9H).
