70% |
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An analytical sample was prepared by dissolving in 210 mL of hot hexanes, cooling, then concentrating to 50percent of the original volume. Cooling in an ice bath with rapid stirring provided 35.5 g (49percent recovery) of a brown, granular solid (m.p. 68-70° C.). 1H NMR (CDCl3): d 7.43 (t, J=27 Hz, 2H), 7.13 (t, J=20 Hz, 1H), 5.94 (s, 2H), 2.02 (s, 6H); 13C NMR (CDCl3) d 158.3 (d, J=254 Hz), 131.6, 128.9, 127.8 (d, J=3 Hz), 122.0, 120.3 (d, J=23 Hz), 106.4, 12.4; MS (El): m/z 268 (100). 1-(2-Fluoro-4-methoxyphenyl)-2,5-dimethyl-1H-pyrrole: The crude product from the previous reaction (1-(2-fluoro-4-iodo-phenyl)-2,5-dimethyl-1 H-pyrrole, 70.0 g, 222 mmol) was dissolved in 230 mL of MeOH and 70 mL of DMF. To this solution was added NaOMe (35.9 g, 666 mmol, 3.0 eq) and CuCl (3.3 g, 31 mmol, 15 mol percent). The resulting mixture was warmed to reflux for 4 h. After cooling to room temperature, isopropyl ether (IPE) (500 mL), 5percent aqueous NH4Cl (220 mL), and water (350 mL) were added, and the mixture was stirred overnight. The mixture was then filtered through celite, the layers were separated, and the aqueous layer extracted with 350 mL of IPE. The combined organic extracts were then washed with 10percent aqueous NH4OH (200 mL), and passed through a pad of silica gel (100 g). Concentration provided a brown oil, which crystallized upon standing (45.2 g, 93percent yield). Recrystallization from 135 mL of hot hexane provided 30.1 g (62percent yield) of product as a brown solid, m.p. 67-69° C. 1H NMR (CDCl3): d 7.12 (t, J=8 Hz, 1H), 6.75 (d, J=8 Hz, 1H), 6.73 (s, 1H), 5.89 (s, 2H), 3.82 (s, 3H), 1.97 (s, 6H); 13C NMR (CDCl3) (9 of 10 lines observed) d 159.1 (d, J=260 Hz), 130.7, 129.5, 109.9 (d, J=3 Hz), 106.0, 105.6, 102.3 (d, J=25 Hz), 55.7, 12.4; MS (El): m/z 219 (100). 2-Fluoro-4-methoxyaniline: A 2 L round bottom flask is charged with 1-(2-fluoro-4-methoxy-phenyl)-2,5-dimethyl-1H-pyrrole (60.0 g, 271 mmol), H2NOH*HCl (188 g, 2.71 mol, 10 eq), EtOH (600 mL), water (300 mL), and Et3N (76 mL, 0.54 mol), then warmed to reflux for 16 h. After cooling to room temperature, the reaction mixture is slowly poured into 1.7 L of ice-cold 1 N HCl, and washed with two 500 mL portions of IPE. The aqueous phase was then brought to pH 10 by careful addition of 6 N NaOH, and extracted with two 500 mL portions of IPE. The organic extracts were concentrated to provide an oily solid, which was filtered, rinsing with additional IPE (the solid was not related to the aniline product by 1H nmr analysis, and is presumably some acetonylacetone related by-product of the deprotection). Further concentration of the IPE solution provided a brown oil (36 g, 98percent yield), which was recrystallized from 200 mL of hot IPE, to provide 26.8 g (70percent yield) of 2-fluoro-4-methoxyaniline 1 as a brown solid, m.p. 46-47° C. (lit 47-48° C.). Spectral data (1H nmr, mass spec) were identical to samples prepared by the literature method (Aust. J. Chem. 1972, 25, 2621-2629). |