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1、294Hari C. Bajaj et al /Int.J. ChemTech Res.2010,2(1) International Journal of ChemTech Research CODEN (USA): IJCRGG ISSN: 0974-4290 Vol.2, No.1, pp 289-294, Jan-Mar 2010 Ionic Liquid Mediated One Pot Synthesis of Substituted 2,4,6-TriarylpyridinesPravin G. Ingole, Sumit V. Jadhav and Hari C. Bajaj*
2、Discipline of Inorganic Material and Catalysis,Central Salt and Marine Chemicals Research Institute,Council of Scientific and Industrial Research (CSIR) G.B.Marg, Bhavnagar-364002, Gujarat-India*Corres. Author: Tel: +91-278-2567760,Fax: +91-278-2567562Abstract: A novel system for the synthesis of se
3、ries of 2,4,6-triarylpyridines and their hydroxyl substituted analogues using cheap and easy to synthesize ionic liquid, Ethyl ammonium nitrate (EAN) as a benign reaction medium is demonstrated. The reaction of acetophenone or p-hydroxyacetophenone with aryl aldehydes in EAN, in the presence of base
4、, followed by treatment with ammonium acetate affords title compounds in significant yields using a one pot procedure. A sequential Aldol condensation and Michael addition reactions in ionic liquid, yields 1,5-diones, which can be readily converted to expected triarylpyridines, via ring closure with
5、 ammonium acetate. The significance of our findings relates to reducing the use of volatile organic solvents, simplicity of the process, as well as its good yields, mild conditions and low costs.Keywords: Triarylpyridine; Ionic liquid; Ethyl ammonium nitrate; Green chemistry.Introduction The N-heter
6、ocyclic compounds comprising Krohnke type pyridines and other substituted pyridines such as 2,4,6-triarylpyridines are prominent synthons in supramolecular chemistry, as a consequence of their -stacking ability along with directional H-bonding capacity. Moreover this class of compound is identified
7、as very useful intermediate in the development of molecules for pharmaceutical or biological interest. Rich coordination properties of these compounds have been greatly exploited for the development of nanoscale metallosupramolecular architectures 1. Pyridines exhibit range of biological activities
8、as; antimalarial, anticonvulsant, anesthetic, antioxidant, antibacterial and antiparasitic properties 2,3. In recent years these compounds are deeply investigated as potential candidates for calcium channel blockers and as antiviral agents 4. Moreover, pyridine derivatives have remarkable versatilit
9、y in synthetic organic chemistry as intermediates in the preparation of natural products and as ligands to be used in asymmetric synthesis 5. Some analogues of pyridines are also highlighted as useful intermediates in the synthesis of pesticides, desiccants, surfactants and so forth 6,7. For the div
10、erse range of potential applications, easy access to differently functionalized Krohnke type triarylpyridines on a large scale and high yields is a prerequisite. Numbers of methods have been reported for the synthesis of these compounds either involving the condensation of 1, 5-diketones with formam
11、ide-formic acid 8 or by other synthetic procedures such as Chichibabin method 9,10. Successful synthesis of Krohnke type pyridines is also reported through the reaction of N-phenacylpyridinium salts with , -unsaturated ketones in the presence of ammonium acetate 11 however, the pyridinium salts and
12、the unsaturated ketones have to be synthesized first, turning this method relatively expensive. More recently many improved processes for synthesis of Krohnke type pyridines have been established, involving variety of precursors such as, -ketoketene dithioacetals 12, N-phosphinylethanimines 13 and l
13、ithiated -enaminophosphonates 14.However, most of the established methodologies suffer from several disadvantages, as multi-step procedures, long reaction time, use of toxic reagents and volatile organic compounds (VOCs). As a consequence, for the stringent and growing environmental regulations, org
14、anic chemists are requested to develop environmentally benign synthetic methods with minimization of waste, a foremost requirement in principles of green chemistry 15. Among the environment friendly approaches to synthesize triarylpyridines; microwave assisted method using polyethylene glycol (PEG)
15、is been demonstrated by Huang et al 16. In a typical attempt to avoid solvent media Heravia et al 17 have synthesized target compounds in reasonable yields by using heteropolyacids as a catalyst, whereas Wu et al 18 have synthesized substituted triarylpyridines via catalyst free Dielsalders reaction. To the date PEG mediated synthesis of triarylpyridines via 1, 5-diketone intermediate reported by Raston et al
