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Catalyst: and solvent-free synthesis of imidazo[1,2-a]pyridines
Zhu, Dong-Jian;Chen, Jiu-Xi;Liu, Miao-Chang;Ding, Jin-Chang;Wu, Hua-Yue;
Journal of the Brazilian Chemical Society , 2009, DOI: 10.1590/S0103-50532009000300012
Abstract: a highly efficient and facile method has been described for the synthesis of imidazo[1,2-a]pyridines in good to excellent yields by condensation of the α-haloketones (arcochxr2, ar = c6h5, 4-meoc6h4, 4-clc6h4, 2,4-cl2c6h3; x = br, cl; r2 = h, ch3) with 2-aminopyridines without the use of any additional catalyst and solvent.
Fluorescent property of 3-hydroxymethyl imidazo[1,2-a]pyridine and pyrimidine derivatives
Stephania Velázquez-Olvera, Héctor Salgado-Zamora, Manuel Velázquez-Ponce, Elena Campos-Aldrete, Alicia Reyes-Arellano, Cuauhtémoc Pérez-González
Chemistry Central Journal , 2012, DOI: 10.1186/1752-153x-6-83
Abstract: Compounds of both series emitted light in organic solvents dilutions as well as in acidic and alkaline media. Quantitative fluorescence spectroscopy determined that both fused heterocycles fluoresced more intensely than the parent unsubstituted imidazo[1,2-a]azine fluorophore. In particular, 3-hydroxymethyl imidazo[1,2-a]pyridines fluoresced more intensely than 3-hydroxymethyl imidazo[1,2-a]pyrimidines, the latter emitting blue light at longer wavelengths, whereas the former emitted purple light.It was concluded that in most cases the hydroxymethyl moiety did act as an enhancer of the fluorescence intensity, however, a comparison made with the fluorescence emitted by 2-aryl imidazo[1,2-a]azines revealed that in some cases the hydroxymethyl substituent decreased the fluorescence intensity.In the past few years a growing interest in the chemistry of imidazo[1,2-a]pyrimidines and pyridines has been developed due to the extent of their applications in pharmacological science. Indeed they are known for their anxiolytic [1], cardiovascular [2], analgesic [3,4], antihypertensive [4] and neuroleptic [5,6] among other activities [7-9]. However, imidazo[1,2-a]pyridines and pyrimidines are also attractive due to their physicochemical properties exhibited, namely the fluorescent activity. Several studies concerning the effects of substituents on the fluorescent properties of imidazo[1,2-apyridines have been carried out, for instance, 2-phenyl (or 2-(2-naphthyl)) and/or 7-methyl substitution caused no deterioration of the fluorescent property. The amino or dimethylamino substitution at the 4'-position of 2-phenyl imidazo[1,2-apyridine shifted the fluorescence to the visible region in polar solvents [10]. From a comparative spectroscopy study performed on several imidazo[1,2-a]pyridines and pyrimidines, it was observed that substitution of a proton for methyl, carboxyl, or amino group increased the fluorescence intensity. Fluorescence was destroyed when a ring position carried a
Regiocontrolled Microwave Assisted Bifunctionalization of 7,8-Dihalogenated Imidazo[1,2-a]pyridines: A One Pot Double-Coupling Approach  [PDF]
Emilie Marie,Sébastien Bouclé,Cécile Enguehard-Gueiffier,Alain Gueiffier
Molecules , 2012, DOI: 10.3390/molecules170910683
Abstract: The reactivity of the 7-chloro-8-iodo- and 8-chloro-7-iodoimidazo[1,2-a]pyridines 1a–e diversely substituted on the 2 position, towards Suzuki-Miyaura, Sonogashira, and Buchwald-Hartwig cross-coupling reactions as well as cyanation was evaluated. Various methodologies are proposed to introduce aryl, heteroaryl, alkyne, amine or cyano groups in the two positions depending on the nature of the substituent present in position 2. In both series, the substitution of the iodine atom was totally regioselective and the difficulty was to substitute the chlorine atom in a second step. Until now, only hetero(aryl) groups could be introduced though Suzuki-Miyaura cross-coupling. We overcame this problem evaluating both regioisomers in parallel. The double coupling approach was also studied allowing the one pot Suzuki/Suzuki, cyanation/Sonogashira and cyanation/Buchwald reactions leading to polyfunctionnalized imidazo[1,2-a]pyridines.
Intramolecular H-bonding interaction in angular 3-pi-EWG substituted imidazo[1,2-a]pyridines contributes to conformational preference
Manuel Velázquez-Ponce, Héctor Salgado-Zamora, Hugo A Jiménez-Vázquez, Maria Elena Campos-Aldrete, Rogelio Jiménez, Humberto Cervantes, Taibi Ben Hadda
Chemistry Central Journal , 2013, DOI: 10.1186/1752-153x-7-20
Abstract: Theoretical calculations were performed aimed to obtain evidence of the existence of an intramolecular non-bonding interaction between H-5 and the oxygen atom of the EWG. Results derived from conformational and vibrational analysis at the DFT B3LYP/6-311++G(d,p) level of theory, the determination of Bond Critical Points derived from AIM theory, and the measurement of some geometrical parameters, support the hypothesis that the higher stability of the prevailing conformation in these molecules (that in which the oxygen of the EWG is oriented towards H-5) has its origin in an intramolecular interaction,Computational calculations predicted correctly the conformational preferences in angular 3-pi-EWG-substituted imidazo[1,2-a]pyridines. The existence of an electrostatic hydrogen bond between H-5 and the oxygen atom of the pi-EWG was supported by several parameters, including X-ray crystallography. The existence of such structural array evidently impacts the H-5 chemical shift.
Synthesis of 2-(5-Nitropyrid-2-yl)-3-(4-substitutedphenyl)aminoisoxazol-5(2H)-ones and Their Rearrangements to Imidazo[1,2-a]- pyridines and Indoles with Triethylamine  [PDF]
J. Khalafy,D. Setamdideh,K. Akbari Dilmaghani
Molecules , 2002, DOI: 10.3390/71200907
Abstract: 3-(4-Substitutedphenyl)aminoisoxazol-5(2H)-ones, substituted on nitrogen with a nitropyridine group, react with triethylamine to give imidazo[1,2-a]pyridines and indoles. With 4-bromophenyl and 4-methylphenyl group substituents only imidazopyridines are formed, but the 4-methoxyphenyl derivative gave a 3:1 mixture of the corresponding imidazo[1,2-a]pyridine and 2-pyridylaminoindole, respectively.
Golden Research Thoughts , 2013, DOI: 10.9780/22315063
Abstract: Prompted by the varied biological activities of imidazo[1,2-a]pyridines and Mannich bases, a series of Mannich bases were prepared by condensing 2-(4- bromophenyl)imidazo[1,2-a]pyridine with dif erent secondary amines andformaldehyde in the presence of acid catalyst. The structures of these novel compounds were confirmed on the basis of spectral data. All the title compounds were screened for their antimicrobial activities. The screening data indicated that tested compounds showed good antimicrobial activity
One-Pot Three-Component Synthesis of Imidazo[1,5-a]pyridines  [PDF]
Abbas Rahmati, Zahra Khalesi
International Journal of Organic Chemistry (IJOC) , 2011, DOI: 10.4236/ijoc.2011.12003
Abstract: A one-pot three component condensation synthesis of imidazo[1,5-a]pyridines using of various aromatic aldehydes and dipyridil ketone with ammonium acetate in the presence of Lithium chloride as catalyst in good yields under microwave irradiation has been described.
Large-Scale Solvent-Free Chlorination of Hydroxy-Pyrimidines, -Pyridines, -Pyrazines and -Amides Using Equimolar POCl3  [PDF]
Han Wang,Kun Wen,Le Wang,Ye Xiang,Xiaocheng Xu,Yongjia Shen,Zhihua Sun
Molecules , 2012, DOI: 10.3390/molecules17044533
Abstract: Chlorination with equimolar POCl3 can be efficiently achieved not only for hydroxypyrimidines, but also for many other substrates such as 2-hydroxy-pyridines, -quinoxalines, or even -amides. The procedure is solvent-free and involves heating in a sealed reactor at high temperatures using one equivalent of pyridine as base. It is suitable for large scale (multigram) batch preparations.
Ionic liquid catalyzed convenient synthesis of imidazo[1,2-a]quinoline under sonic condition
Patel, Devji S.;Avalani, Jemin R.;Raval, Dipak K.;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012005000051
Abstract: an efficient protocol for the synthesis of imidazo[1,2-a]quinoline from aldehydes, enaminones, and malononitrile using 1,8-diazabicyclo[5.4.0]-undec-7-en-8-ium acetate ([dbu][ac]) as a catalyst under ultrasound irradiation is described. compared with other methods, this new method has the advantages of easier work-up, milder reaction conditions, high yields and environmentally benign procedure.
Ethyl 8-(4-nitrophenyl)imidazo[1,2-a]pyridine-7-carboxylate
Gui-Yun Duan,Yu-Juan Zhang,Ben-Qian Hao
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810047938
Abstract: In the title compound, C16H13N3O4, the imidazo[1,2-a]pyridine and benzene rings make a dihedral angle of 56.21 (2)°. The crystal packing is stabilized by weak π–π stacking interactions [centroid–centroid distances = 3.787 (2) ] and C—H...O intermolecular hydrogen-bonding interactions.
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