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With N-Bromosuccinimide In N,N-dimethyl-formamide at 20℃; for 120.5 h;
(a); 5.76 g (40.1 mmol) of 4-chloro-2-methoxypyridine was dissolved in 20 ml of dimethylformamide, and a dimethylformamide (20 ml) solution of 8.01 g of N-bromosuccinimide (98percent, 44.1 mmol) was dropwise added over a period of 30 minutes. After stirring at room temperature for 2 days, an unreacted material was confirmed, and thus 2.85 g of N-bromosuccinimide (98percent, 16 mmol) was further added, followed by stirring at room temperature further for 3 days. The reaction mixture was poured into 250 ml of water, followed by extraction with ethyl ether (100 ml each) three times. The organic layer was washed with water (100 ml), a sodium thiosulfate aqueous solution (100 ml) and then a saturated sodium chloride solution (100 ml), dried over magnesium sulfate and subjected to filtration, and the solvent was distilled off under reduced pressure. The obtained crude product was purified by silica gel chromatography to obtain 7.10 g (yield: 80percent) of 5-bromo-4-chloro-2-methoxypyridine. 1H-NMR(CDCl3, 400MHz): δ (ppm) =3.91 (s, 3H), 6. 89 (s,1H), 8.28(s,1H)
50%
With N-Bromosuccinimide In N,N-dimethyl-formamide at 90℃; for 8 h;
To a solution of compound 2 (28.7 g. 0.2 mol) in DMF (50 mL) was added NBS (35.5 g, 0.2 mol). The mixture was heated at 90°C for 8 hours. The crude compound 3 was collected by filtration. (22 g, 50percent yield).
Stage #1: With lithium diisopropyl amide In tetrahydrofuran; hexane at -78℃; for 1 h; Stage #2: at -78℃; for 1 h;
To a solution of LDA (1.0 M solution in hexane) (29.3 mL, 29.3 mmol) in THF (45 mL) was added a solution of 4-chloro-2-methoxypyridine (3.5 g, 24.38 mmol) in THF (8 mL) dropwise at -78 °C. The reaction mixture turned into light yellow solution and was stirred at-78 °C for 1 h, then DMF (3.78 mL, 48.8 mmol) was added dropwise. The reaction mixture was stirred at -78 °C for lh. The reaction mixture was quenched with saturated NH4C1 solution at -78 °C and the resulting mixture was stirred for 10 min and warmed up to rt. The resulting mixture was mixed with saturated NaHC03 solution and ethyl acetate. The organic layer was separated and washed with saturated NaHC03 solution, dried over MgS04. The filtrate was concentrated in vacuo. The residue was dissolved in DCM, purified via silica gel flash column chromatography, eluting with 0-25percent ethyl acetate in hexane to give Intermediate 24A (white solid, 2.6 g, 15.15 mmol, 60percent yield). LC-MS Anal. Calc'd for CvHeClNC 171.01, found [M+H] 172.1. Tr = 0.71 min (Method A). NMR (499MHz, chloroform-d) δ 10.47 (s, 1H), 8.20 (d, J=5.5 Hz, 1H), 7.01 (d, J=5.5 Hz, 1H), 4.08 (s, 3H)
To a solution of LDA (1.0 M solution in hexane) (29.3 mL, 29.3 mmol) in THF (45 mL) was added a solution of 4-chloro-2-methoxypyridine (3.5 g, 24.38 mmol) in THF (8 mL) dropwise at -78 C. The reaction mixture turned into light yellow solution and was stirred at-78 C for 1 h, then DMF (3.78 mL, 48.8 mmol) was added dropwise. The reaction mixture was stirred at -78 C for lh. The reaction mixture was quenched with saturated NH4C1 solution at -78 C and the resulting mixture was stirred for 10 min and warmed up to rt. The resulting mixture was mixed with saturated NaHC03 solution and ethyl acetate. The organic layer was separated and washed with saturated NaHC03 solution, dried over MgS04. The filtrate was concentrated in vacuo. The residue was dissolved in DCM, purified via silica gel flash column chromatography, eluting with 0-25% ethyl acetate in hexane to give Intermediate 24A (white solid, 2.6 g, 15.15 mmol, 60% yield). LC-MS Anal. Calc'd for CvHeClNC 171.01, found [M+H] 172.1. Tr = 0.71 min (Method A). NMR (499MHz, chloroform-d) delta 10.47 (s, 1H), 8.20 (d, J=5.5 Hz, 1H), 7.01 (d, J=5.5 Hz, 1H), 4.08 (s, 3H)
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