Reaction Steps
2-Bromo-4-nitrobenzoic acid (6.2 g, 25.3 mmol) was dissolved in MeOH (120 mL), and SOCl2 (5.5 mL, 75.9 mmol) was added dropwise at 0° C. The reaction mixture was refluxed for 6 h. The reaction solvent was concentrated to dryness. Residual SOCl2 was removed by co-evaporation with CH2Cl2 (×3). The solid was dried under vacuum to afford methyl 2-bromo-4-nitrobenzoate in 99.5% (6.52 g) yield as a light yellow solid. 1H-NMR (CDCl3, 400 MHz) δ 8.50 (1H, s, Ar), 8.21 (1H, d, J=8.4 Hz, Ar), 7.91 (1H, d, J=8.4 Hz, Ar), 3.97 (3H, s, OCH3); 13C-NMR (CDCl3, 100 MHz) δ 165.2, 149.2, 137.9, 131.7, 129.1, 122.1, 122.0, 53.1; MS (ESI) m/z Calcd for C8H6BrNO4 (M+): 259.0, Found: 260.1 (M+H+). Next, the nitro group of methyl 2-bromo-4-nitrobenzoate (6.38 g, 24.6 mmol) was chemoselectively reduced with 5 nCl2.2H2O (27.8 g, 123.2 mmol) in a manner similar to that described for compound 6 to deliver methyl 4-amino-2-bromobenzoate in 96.0% (5.41 g) yield as a yellow solid. 1H-NMR (CDCl3, 400 MHz) δ 7.74 (1H, d, J=8.8 Hz, Ar), 6.90 (1H, d, J=1.6 Hz, Ar), 6.55 (1H, dd, J=8.8 Hz, 1.6 Hz, Ar), 4.06 (2H, s, NH2), 3.83 (3H, s, OCH3); 13C-NMR (CDCl3, 100 MHz) δ 165.9, 150.4, 133.6, 124.1, 119.7, 119.6, 112.7, 51.8; MS (ESI) m/z Calcd for C8H8BrNO2 (M+): 229.0, Found: 230.1 (M+H+). Finally, a solution of sulfuric acid (98%, 6 mL) in H2O (75 mL) was added to methyl 4-amino-2-bromobenzoate (1.23 g, 5.38 mmol) and the resulting suspension was heated to 90° C., then stirred for 5 h at this temperature. The reaction mixture was cooled to 0° C. and a solution of NaNO2 (384 mg, 5.57 mmol) in H2O (5 mL) was added dropwise, then the reaction was allowed to warm to ambient temperature. The reaction mixture was then added to a solution of sulfuric acid (98%, 6 mL) in H2O (75 mL) that had been preheated to 90° C. The reaction mixture was stirred at 90° C. for 1 h, and then allowed to cool. The reaction mixture was partitioned between EtOAc (200 mL) and aqueous solution. The organic layer was collected, dried over anhydrous Na2SO4, filtered, concentrated and purified by silica column chromatography (35% EtOAc in hexanes) to afford compound 10 in 41.1% (508 mg) yield as a light brown solid. 1H-NMR (CDCl3, 400 MHz) δ 7.76 (1H, d, J=8.8 Hz, Ar), 7.09 (1H, s, Ar), 6.75 (1H, d, J=8.8 Hz, Ar), 3.84 (3H, s, OCH3); 13C-NMR (CDCl3, 100 MHz) δ 166.2, 160.3, 133.5, 123.4, 122.1, 121.4, 114.3, 52.1; MS (ESI) m/z Calcd for C8H7BrO3 (M+): 230.0, Found: 231.0 (M+H+).
