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Stage #1: at 20℃; Stage #2: With sodium hydrogencarbonate In water; ethyl acetateSaturated solution
Step a: 3-Bromo-5-nitropyridin-2-amine To a solution of 5-nitro-pyridin-2-ylamine (30 g, 0.22 mol) in acetic acid (200 mL) at 10° C. was added Br2 (38 g, 0.24 mol) dropwise. After addition, the mixture was stirred at 20° C. for 30 min. The solid was filtered and then dissolved in ethyl acetate (200 mL). The mixture was basified to pH 8-9 with saturated aqueous NaHCO3. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (100 mL*3). The combined organic layers were washed with water, brine, dried over Na2SO4 and concentrated under vacuum to afford 3-bromo-5-nitropyridin-2-amine (14.8 g, 32percent). 1H-NMR (CDCl3, 400 MHz) δ 8.94 (d, J=2.4 Hz, 1H), 8.50 (d, J=2.4 Hz, 1H), 5.67 (brs, 2H).
31%
With N-Bromosuccinimide In toluene at 80℃; for 1 h; Inert atmosphere
General procedure: Under an Ar atmosphere, N-chlorosuccinimide (0.53 g,3.95 mmol) was added to a solution of compound 1 (0.50 g,3.59 mmol) in anhydrous toluene (7.18 mL). The resulting reactionmixture was stirred at 80 C for 1 h. The reaction mixture wascooled to room temperature and 15 mL of H2O was added to thismixture. It was then extracted with EtOAc, washed with sat.NaHCO3 solution, brine, concentrated under vacuum, and purifiedby column chromatography (KANTO 60 N, Hex/EtOAc = 80/20 to60/40) to give a yellow solid 2a (0.40 g, 2.30 mmol, 64percent).
Reference：
[1] Patent: US2009/253736, 2009, A1, . Location in patent: Page/Page column 25
[2] Bioorganic and Medicinal Chemistry, 2017, vol. 25, # 14, p. 3853 - 3860
[3] Zhurnal Russkago Fiziko-Khimicheskago Obshchestva, 1920, vol. 50, p. 494[4] Chemisches Zentralblatt, 1923, vol. 94, # III, p. 1021
[5] Zhurnal Obshchei Khimii, 1940, vol. 10, p. 1827,1836[6] Chemisches Zentralblatt, 1940, vol. 111, # II, p. 614
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[ 4214-76-0 ]
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[ 25045-82-3 ]
Yield
Reaction Conditions
Operation in experiment
77.6%
Stage #1: With hydrogenchloride In ethanol at 20℃; Reflux Stage #2: at 20℃;
In a 250 mL single-necked flask, bromoacetaldehyde diethyl acetal (42.5 g, 215.7 mmol) was dissolved in 1 mol / L HCL(120 mL) and ethanol (20 mL), stirred at room temperature for 30 min, heated to reflux, stirred until the solution was clear, cooled to room temperature,Add NaHCO3 adjusted to near neutral,2-Amino-5-nitropyridine (15.0 g, 107.8 mmol) was added and reacted at room temperatureovernight. The reaction was completed, extracted with ethyl acetate (100mL × 3), the organic phase was collected and the solvent was evaporated to dryness under reduced pressure. The residue was passed through a silica gel column (PE:EA = 2: 1) to give 13.7 g of 6-nitroimidazo [1,2-a] pyridine yellow-brown crystals in a yield of 77.6percent.
Reference：
[1] Patent: CN107129496, 2017, A, . Location in patent: Paragraph 0026-0028; 0014-0016; 0020-0022
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[ 4214-76-0 ]
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[ 25045-82-3 ]
Reference：
[1] Yakugaku Zasshi, 1949, vol. 69, p. 496[2] Chem.Abstr., 1950, p. 4474
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