Synlett, Inhaltsverzeichnis Synlett 2012; 23(18): 2635-2638DOI: 10.1055/s-0032-1317323 letter © Georg Thieme Verlag Stuttgart · New YorkSimple and Efficient One-Pot Synthesis of Imidazo[1,2-a]pyridines Catalyzed by Magnetic Nano-Fe3O4–KHSO4·SiO2 Tirumaleswararao Guntreddi Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India Fax: +91(542)2368127 eMail: knsingh@bhu.ac.in , Bharat Kumar Allam Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India Fax: +91(542)2368127 eMail: knsingh@bhu.ac.in , Krishna Nand Singh* Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, India Fax: +91(542)2368127 eMail: knsingh@bhu.ac.in› InstitutsangabenArtikel empfehlen Abstract Artikel einzeln kaufen Alle Artikel dieser Rubrik 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. Key words Key wordsmulticomponent reactions - transition metals - heterocycles - heterogeneous catalysis - iron Volltext Referenzen References 1 Zhu J, Bienaymé H. Multicomponent Reactions. Wiley-VCH; Weinheim: 2005 2 Dömling A, Wang W, Wang K. Chem. Rev. 2012; 112: 3083 3a Horton DA, Bourne GT, Smythe ML. Chem. Rev. 2003; 103: 893 3b Constantino L, Barlocco D. Curr. Med. Chem. 2006; 13: 65 4a Oishi H, Takano K.-i, Tomita K, Takebe M, Yokoo H, Yamazaki M, Hattori Y. Am. J. Physiol. Lung Cell Mol. Physiol. 2012; 303: L130 4b Yamane I, Hagino H, Okano T, Enokida M, Yamasaki D, Teshima R. Arthritis Rheum. 2003; 48: 1732 4c Kim O, Jeong Y, Lee H, Hong S.-S, Hong S. J. Med. Chem. 2011; 54: 2455 4d Trabanco AA, Tresadern G, Macdonald GJ, Vega JA, de Lucas AI, Matesanz E, García A, Linares ML, de Diego SA. A, Alonso JM, Oehlrich D, Ahnaou A, Drinkenburg W, Mackie C, Andres JI, Lavreysen H, Cid JM. J. Med. Chem. 2012; 55: 2688 4e Kamal A, Surendranadha Reddy J, Janaki Ramaiah M, Dastagiri D, Vijaya Bharathi E, Victor Prem Sagar M, Pushpavalli SN. C. V. L, Ray P, Pal-Bhadra M. Med. Chem. Commun. 2010; 1: 355 4f Langer SZ, Arbilla S, Benavides J, Scatton B. Adv. Biochem. Psychopharmacol. 1990; 46: 61 4g Lhassani M, Chavignon O, Chezal J.-M, Teulade J.-C, Chapat J.-P, Snoeck R, Andrei G, Balzarini J, De Clercq E, Gueiffier A. Eur. J. Med. Chem. 1999; 34: 271 5a Chernyak N, Gevorgyan V. Angew. Chem. Int. Ed. 2010; 49: 2743 5b Reddy BV. S, Reddy PS, Reddy YJ, Yadav JS. Tetrahedron Lett. 2011; 52: 5789 5c Liu P, Fang L.-s, Lei X, Lin G.-q. Tetrahedron Lett. 2010; 51: 4605 5d Mishra S, Ghosh R. Synthesis 2011; 3463 6a Polshettiwar V, Luque R, Fihri A, Zhu H, Bouhrara M, Basset JM. Chem. Rev. 2011; 111: 3036 6b Shylesh S, Schunemann V, Thiel WR. Angew. Chem. Int. Ed. 2010; 49: 3428 6c Firouzabadi H, Iranpoor N, Gholinejad M, Hoseini J. Adv. Synth. Catal. 2011; 353: 125 6d Zhang Z.-H, Lu H.-Y, Yang S.-H, Gao J.-W. J. Comb. Chem. 2010; 12: 643 6e Martínez R, Ramón DJ, Yus M. Adv. Synth. Catal. 2008; 350: 1235 7a Allam BK, Singh KN. Tetrahedron Lett. 2011; 52: 5851 7b Allam BK, Singh KN. Synthesis 2011; 1125 7c Singh N, Singh SK, Khanna RS, Singh KN. Tetrahedron Lett. 2011; 52: 2419 7d Kumari K, Raghuvanshi DS, Jouikov V, Singh KN. Tetrahedron Lett. 2012; 53: 1130 7e Raghuvanshi DS, Singh KN. Tetrahedron Lett. 2011; 52: 5702 7f Raghuvanshi DS, Singh KN. Synlett 2011; 373 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. 9 For the preparation of KHSO4·SiO2, see: Goswami N, Das RN, Borthakur N. Ind. J. Chem., Sect. B: Org. Chem. Incl. Med. Chem. 2007; 46: 1893 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.
