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Synlett 2012; 23(18): 2635-2638
DOI: 10.1055/s-0032-1317323
DOI: 10.1055/s-0032-1317323
letter
Simple and Efficient One-Pot Synthesis of Imidazo[1,2-a]pyridines Catalyzed by Magnetic Nano-Fe3O4–KHSO4·SiO2
Weitere Informationen
Publikationsverlauf
Received: 04. August 2012
Accepted after revision: 05. September 2012
Publikationsdatum:
01. Oktober 2012 (online)
Abstract
The present report highlights a magnetic nano-Fe3O4–KHSO4·SiO2 catalyzed synthesis of imidazo[1,2-a]pyridines. The synthetic strategy adopted is expedient, versatile, and offers good to excellent yields from readily available starting materials.
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- 8 General Experimental Procedure: To an oven-dried 25 mL round-bottom flask containing a magnetic stir bar was added 2-aminopyridine (1 mmol, 94.1 mg), aldehyde (1 mmol), KHSO4·SiO2 (150 mg, 0.032 mmol with respect to KHSO4), and anhyd toluene (2 mL). The mixture was stirred for 15 min and to it was then added alkyne (1.2 mmol) and nano-Fe3O4 [<50 nm particle size, ≥98% trace metals basis (Aldrich)] (0.1 mmol, 23.2 mg). The total reaction mixture was refluxed at 110 °C for the appropriate time. After completion of the reaction (monitored by TLC), EtOAc was added (10 mL), the magnetic Fe3O4 nanoparticles were collected on the magnetic stir bar, and the mixture was filtered through a porous plug. The filtrate was concentrated under reduced pressure and the crude product thus obtained, was purified by silica gel column chromatography (EtOAc–hexane, 1:9). The pure products were characterized based upon their physical and spectroscopic properties. Spectroscopic Data of the Representative Compounds: 3-Benzyl-2-(3-chlorophenyl)imidazo[1,2-a]pyridine (4c): White solid; mp = 141–142 °C. 1H NMR (300 MHz, CDCl3): δ = 7.77 (s, 1 H), 7.65–7.53 (m, 3 H), 7.27–7.22 (m, 4 H), 7.21–7.10 (m, 2 H), 7.07 (d, J = 6.6 Hz, 2 H), 6.68–6.64 (m, 1 H), 4.42 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 143.7, 142.2, 136.1, 135.9, 134.4, 132.0, 129.9, 129.6, 129.3, 128.1, 127.9, 127.7, 126.9, 126.3, 124.8, 123.3, 118.0, 117.7, 112.4, 29.9 ppm. 3-Benzyl-2-(4-tolyl)imidazo[1,2-a]pyridine (4i): Pale yellow solid; mp = 160–161 °C. 1H NMR (300 MHz, CDCl3): δ = 7.69 (t, J = 8.1 Hz, 4 H), 7.26 (br s, 5 H), 7.16–7.13 (m, 3 H), 6.70 (br s, 1 H), 4.49 (s, 2 H), 2.39 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 144.6, 144.0, 137.7, 136.6, 131.9, 129.0, 128.9, 128.2, 127.6, 126.7, 124.1, 123.1, 117.5, 117.3, 112.0, 30.1, 21.1 ppm.
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- 10 Reusability of magnetic nano-Fe3O4: After completion of the reaction EtOAc was added and the Fe3O4-nanoparticles were recovered by the application of an external magnet. The recovered nanoparticles were thoroughly washed with Et2O, dried at 130 °C for 1 h and then reused for a new catalytic cycle.