Sulfuric Acid → 2-(4-Tert-butyl-benzoylamino)-4-hydroxy-benzoic acid methyl ester

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To a solution of 4-amino-2-(4-tert-butyl-benzoylamino)-benzoic acid methyl ester (0.711 g, 2.18 mmol) in trifluoroacetic acid cooled to 0° C. was added NaNO2 (0.182 g, 2.64 mmol, 1.21 eq) as a solution in water (4 mL) and the reaction was stirred for 5 minutes. It was then added dropwise to a 30% solution of H2SO4 (50 mL) at 65° C. and stirred for 15 minutes. It was 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-hydroxy-benzoic acid methyl ester (0.508, 71%) as a white solid. mp=146.0-148.4° C.; mass spectrum (−ES, M−H) m/z 326. 1H NMR (400 MHz, DMSO-d6); δ 11.95 (bs, 1H), 10.60 (bs, 1H), 8.26 (d, 1H), 7.88 (m, 3H), 7.62 (d, 2H), 6.58 (dd, 1H), 3.85 (s, 3H), 1.32 (s, 9H). Elemental analysis: Calcd. for C19H21NO4: C, 69.71; H, 6.47; N, 4.28, Found: C, 69.20; H, 6.54; N, 4.17.

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