ORIGINAL PAPER Highly efficient, one-pot, solvent-free synthesis of 2,4,6- triarylpyridines using a Brønsted-acidic ionic liquid as reusable catalyst Abolghasem Davoodnia • Mehdi Bakavoli • Raheleh Moloudi • Niloofar Tavakoli-Hoseini • Maryam Khashi Received: 2 February 2010 / Accepted: 11 May 2010 / Published online: 3 June 2010 Ó Springer-Verlag 2010 Abstract A simple, efficient, and green method for syn- thesis of 2,4,6-triarylpyridines by one-pot three-component reaction of acetophenones, aryl aldehydes, and ammonium acetate using 3-methyl-1-(4-sulfonylbutyl)imidazolium hydrogen sulfate [HO 3 S(CH 2 ) 4 MIM][HSO 4 ], a Brønsted- acidic ionic liquid, as an effective and reusable catalyst under solvent-free conditions is described. This method has several advantages, for example simple procedure with an easy work-up, shorter reaction times, and high yields. Keywords Brønsted-acidic ionic liquids Á Multi-component reactions Á 2,4,6-Triarylpyridines Á Solvent-free conditions Introduction Multicomponent reactions (MCRs) have recently received the attention of organic chemists because of the many advantages these reactions over conventional multi-step synthesis and their potential applications in medicinal chemistry for generation of diverse scaffolds and combi- natorial libraries for drug development [1–3]. MCRs contribute to the requirements of an environmentally friendly process by reducing the number of synthetic steps, energy consumption, and waste production. Therefore, discovery for new MCRs and improving already known MCRs are of substantial interest. The presence of the pyridine ring system in a number of natural products, vitamins, and pharmacologically signifi- cant molecules [4] has made it a prime target for scientific research. Literature reports have already established pyri- dines as antimalarials, vasodilators, anesthetics, anticovul- sants, antiepileptics, and agrochemicals such as fungicides, pesticides, and herbicides [5–8]. Also, because of their p-stacking ability, some pyridines are used in supramolecular chemistry [9]. 2,4,6-Triarylpyridines (Kro ¨hnke pyridines) are structur- ally related to symmetrical triaryl-thiopyrylium, triaryl- selenopyrylium, and triaryl-telluropyrylium photosensitizers, which have been recommended for photodynamic cell- specific cancer therapy [10]. These compounds have already been synthesized by reaction of N-phenacylpyrid- inium salts with a,b-unsaturated ketones in the presence of ammonium acetate [11, 12]. However, the pyridinium salts and the unsaturated ketones have to be synthesized first, so this method is relatively expensive. More recently, several new improved methods and procedures for preparation of 2,4,6-triarylpyridines have been reported, for example reaction of a-ketoketene dithioacetals with methyl ketones in the presence of NH 4 OAc [13], reaction of N-phosph- inylethanimines with aldehydes [14], solvent-free reaction of chalcones with ammonium acetate [15], solvent-free reaction between acetophenones, benzaldehydes, and NH 4 OAc in the presence of various catalysts, for example Preyssler type heteropolyacid [16], HClO 4 -SiO 2 [17], and I 2 [18], and the one-pot reaction of acetophenones, benz- aldehydes, and NH 4 OAc without catalyst under microwave irradiation [19]. Ionic liquids (ILs) are salt-type compounds which are liquid at room temperature and have low vapor pressure. Because of the lack of evaporation, they are regarded as promising ‘‘green solvents’’ for replacing the volatile–– A. Davoodnia (&) Á M. Bakavoli Á R. Moloudi Á N. Tavakoli-Hoseini Á M. Khashi Department of Chemistry, Faculty of Sciences, Islamic Azad University, Mashhad Branch, Mashhad, Iran e-mail: adavoodnia@yahoo.com; adavoodnia@mshdiau.ac.ir 123 Monatsh Chem (2010) 141:867–870 DOI 10.1007/s00706-010-0329-x