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Synlett 2014; 25(18): 2636-2638
DOI: 10.1055/s-0034-1379185
DOI: 10.1055/s-0034-1379185
letter
Synthesis of 3-Nitro-2-arylimidazo[1,2-a]pyridines Using Sodium Dichloroiodide
Further Information
Publication History
Received: 15 July 2014
Accepted after revision: 29 August 2014
Publication Date:
17 September 2014 (online)
Abstract
Moderate to good yields of various 3-nitro-2-arylimidazo[1,2-a]pyridines have been easily achieved in the reaction of 2-aminopyridines and nitrostyrenes in the presence of sodium dichloriodide. The procedure is simple and various functional groups are tolerated in this reaction system.
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References and Notes
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- 10 Typical Procedure A mixture of nitrostyrene (1.2 equiv), 2-aminopyridine (1 equiv), and aq NaICl2 (0.1 equiv) in DMF was stirred at 80 °C for 1.5 h. After completion of reaction (monitored by TLC), the reaction mixture was diluted with EtOAc and washed with brine. The organic layer was separated, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure to give the crude product. The product was then purified using silica gel column chromatography (EtOAc–hexane). 3-Nitro-2-phenylimidazo[1,2-a]pyridine (3a) Yellow solid; mp 170–172 °C (lit.9a 172–174 °C). 1H NMR (400 MHz, CDCl3): δ = 9.52 (d, J = 7.2 Hz, 1 H, H-5), 7.92–7.89 (m, 2 H, H-2′ and H-6′-Ph), 7.84 (d, J = 8.8 Hz, 1 H, H-8), 7.68–7.64 (m, 1 H, H-7), 7.52 (t, J = 2.0 Hz, 3 H, H-3′, H-4′, and 5′-Ph), 7.28 (t, 1 H, H-6). IR (KBr): 3061, 3034, 1630, 1531, 1481, 1369, 1219, 929, 761, 694 cm–1. 2-(4-Methoxyphenyl)-3-nitroimidazo[1,2-a]pyridine (3b) Yellow solid; mp 167–169 °C (lit.9a 168–170 °C). 1H NMR (400 MHz, CDCl3): δ = 9.50 (d, J = 6.8 Hz, 1 H, H-5), 7.92 (d, J = 8.8 Hz, 2 H, H-2′ and 6′-Ph), 7.79 (d, J = 8.8 Hz, 1 H, H-8), 7.63 (t, J = 8.0 Hz, 1 H, H-7), 7.24 (d, J = 6.8 Hz, 1 H, H-6), 7.07 (d, J = 8.8 Hz, 2 H, H-3′ and 5′-Ph), 3.87 (s, 3 H, OCH3). IR (KBr): 3016, 2922, 1608, 1541, 1481, 1369, 1211, 921, 758 cm–1. 2-(4-Fluorophenyl)-3-nitroimidazo[1,2-a]pyridine (3d) Yellow solid; mp 224–226 °C (lit.9c 227–228 °C). 1H NMR (400 MHz, CDCl3): δ = 9.52 (d, J = 6.8 Hz, 1 H, H-5), 7.88–7.82 (m, 3 H), 7.69–7.65 (m, 3 H), 7.31–7.27 (m, 1 H). IR (KBr): 3061, 3030, 1604, 1537, 1487, 1334, 1220, 837, 763 cm–1. 3-Nitro-2-(4-nitrophenyl)imidazo[1,2-a]pyridine (3g) Yellow solid, mp 216–218 °C. 1H NMR (400 MHz, CDCl3): δ = 9.54 (d, J = 7.0 Hz, 1 H, H-5), 8.30 (d, J = 8.9 Hz, 2 H, H-2′ and 6′-Ph), 8.13 (d, J = 8.9 Hz, 2 H, H-3′ and 5′-Ph), 7.73 (t, J = 8.2 Hz, 1 H, H-7), 7.66 (d, J = 9.2 Hz, 1 H, H-8), 7.37 (t, J = 7.0 Hz, 1 H, H-6). IR (KBr): 3074, 3032, 1635, 1599, 1514, 1481, 1334, 856, 758 cm–1. 2-(4-Methoxyphenyl)-8-methyl-3-nitroimidazo[1,2-a]pyridine (3j) Yellow solid; mp 148–150 °C. 1H NMR (500 MHz, CDCl3): δ = 9.37 (d, J = 7.2 Hz, 1 H, H-5), 7.94 (d, J = 8.8 Hz, 2 H, H-2′ and 6′-Ph), 7.43 (d, J = 6.8 Hz, 1 H, H-7), 7.15 (t, J = 6.8 Hz, 1 H, H-6), 7.03 (d, J = 8.8 Hz, 2 H, H-3′ and 5′-Ph), 3.84 (s, 3 H, OCH3), 2.71 (s, 3 H, CH3). IR (KBr): 3030, 2922, 1610, 1611, 1580, 1472, 1369, 1238, 1149, 1031, 827, 754 cm–1. 2-(4-Fluorophenyl)-8-methyl-3-nitroimidazo[1,2-a]pyridine (3k) Yellow solid; mp 194–198 °C. 1H NMR (500 MHz, CDCl3): δ = 9.37 (d, J = 6.95 Hz, 1 H, H-5), 7.96–7.92 (m, 2 H, H-2′ and 6′-Ph), 7.46 (d, J = 7.2 Hz, 1 H, H-7), 7.20 (t, J = 7.1 Hz, 3 H, H-6, H-3′, and 5′-Ph) 2.73 (s, 3 H, CH3). IR (KBr): 3053, 2918, 1607, 1539, 1479, 1366, 1238, 1157, 837, 746 cm–1. 5-Methyl-3-nitro-2-phenylimidazo[1,2-a]pyridine (3l) Yellow viscous liquid. 1H NMR (400 MHz, CDCl3): δ = 7.99 (t, 2 H, H-2′ and 6′-Ph), 7.74 (s, 1 H, H-4′-Ph), 7.57 (d, J = 8.8 Hz, 1 H, H-8), 7.44 (t, 2 H, H-3′ and 5′-Ph), 7.37 (t, J = 7.4 Hz, 1 H, H-7), 7.15 (d, J = 6.8 Hz, 1 H, H-6), 2.61 (s, 3 H, CH3). IR (KBr): 3061, 3030, 2920, 1674, 1537, 1483, 1344, 1226, 1153, 947, 825, 775 cm–1.