methyl 4-amino-2-bromobenzoate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a suspension of 2-bromo-4-nitro-benzoic acid methyl ester [100959-22-6] (350 mg, 1.35 mmol) in MeOH (60 mL) were subsequently added tin powder (1.6 g, 13.5 mmol) and 3N aqueous HCl (27.8 mL, 83 mmol). The mixture was stirred overnight at RT. The liquid phase was decanted from the excess tin and neutralized by adding a saturated aqueous NaHCO3 solution. An equal amount of water by volume was added and the water phase was extracted with EtOAc (3×). The combined organics were dried (Phase Separator) and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel (eluent: EtOAc/c-hexane 1:4) to give the title compound as yellow solid. MS (LC/MS): 230 [M+H]+; tR (HPLC conditions b): 2.89 min. The liquid phase was decanted from the excess tin by adding a saturated aqueous NaHCO3 solution An equal amount of water by volume was added the water phase was extracted with EtOAc (3×) The combined organics were dried (Phase Separator) concentrated in vacuo The residue was purified by flash column chromatography on silica gel (eluent: EtOAc/c-hexane 1:4)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A mixture of (2S,4R)-4-fluoro-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester (355 mg, 1.52 mmol), and 4-amino-2-bromo-benzoic acid methyl ester (prepared as described in Part C) (350 mg, 1.52 mmol), HBTU (865 mg, 2.282 mmol) and DIPEA (0.531 mL, 3.04 mmol) in CH2Cl2 (15 mL) was stirred at RT for 60 h. Additional aliquots of (2S,4R)-4-fluoro-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester (180 mg), HBTU (580 mg) and DIPEA (0.265 mL) were added to the mixture, and stirring was continued at RT for 20 h and subsequently at 40° C. for 24 h. The reaction mixture was diluted with CH2Cl2 and the organic layer was washed with water, 1N aqueous HCl (3×), aqueous NaHCO3 solution (2×) and brine, dried (Phase separator) and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel (eluent: EtOAc/c-hexane gradient 1:3 to 1:2) to afford the title compound as a white foam. TLC Rf (EtOAc/c-hexane 1:2)=0.24; MS (LC/MS): 468 [M+Na]+, 388/390 [MH−tBu]+, 345/347 [MH−Boc]+; tR (HPLC conditions b): 4.36 min. stirring was continued at RT for 20 h and subsequently at 40° C. for 24 h the organic layer was washed with water, 1N aqueous HCl (3×), aqueous NaHCO3 solution (2×) and brine dried (Phase separator) concentrated in vacuo The residue was purified by flash column chromatography on silica gel (eluent: EtOAc/c-hexane gradient 1:3 to 1:2)

Conditions: temp:90.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 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+). yield as a light yellow solid yield as a yellow solid The reaction mixture was cooled to 0° C. to warm to ambient temperature had been preheated to 90° C The reaction mixture was stirred at 90° C. for 1 h 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 purified by silica column chromatography (35% EtOAc in hexanes)