To a solution of 4-nitro-anthranilic acid methyl ester (1.500 g, 7.4 mmol) in CH2Cl2 (200 mL) was added triethylamine (8 mL) and 4-tert-butyl benzoyl chloride and the reaction was stirred overnight at rt. It was then poured into brine, extracted with ethyl acetate, dried over MgSO4 and concentrated in vacuo. The residue was purified by flash chromatography using ethyl acetate/hexanes (20/80) to afford 2-(4-tert-butyl-benzoylamino)-4-nitro-benzoic acid methyl ester (1.841 g, 60%) as a yellow solid. mp=146.0-148.4° C.; mass spectrum (−ES, M−H) in/z 355. 1H NMR (400 MHz, DMSO-d6); δ 11.60 (bs, 1H), 9.35 (d, 1H), 8.20 (d, 1H), 8.02 (dd, 1H), 7.90 (d, 2H), 7.64 (d, 2H), 3.95 (s, 3H), 1.36 (s, 9H). Elemental analysis: Calcd. for C19H20N2O5: C, 64.04; H, 5.66; N, 7.86, Found: C, 64.04; H, 5.79; N, 7.76.
