Sulfonic acid functionalized mesoporous SiO2 for solvnt-free synthesis imidazoles

Multicomponent reactions (MCRs), as a general way to improve synthetic efficiency, by virtue of their convergence, productivity, facile execution, and generally high yields of products, have attracted much attention from the point of combinatorial chemistry [1]. The imidazole, being a core molecule in many biological systems [2] and an active component in several drug molecules has attracted attention in recent years. Different substituted imidazoles show variable biological activities. Despite the availability of wide variety of synthetic routes towards imidazoles, only few studies exist for the synthesis of 1,2,4,5-tetrasubstituted imidazoles, which are most widely performed via multi-step routes or via trisubstituted 1H - imidazole in which the nitrogen is substituted in the final step [3] A powerful strategy for the rapid introduction of molecular diversity in the construction of 1,2,4,5-tetrasubstituted imidazoles involves multicomponent reactions (MCRs). Supported solid catalysts have received a great deal of attention in recent years and indeed have been proved versatile in several commercial scale processes [4]. Mesoporous silica materials, including MCM-41 and SBA-15,have been some of the most common supports which emerged as high surface, tunable, and stable alternative materials [5]. In other hand, in recent years, the multicomponent reaction over high surface area porous metal oxide material has been studied. In these studies, the researchers have tried to find the optimized conditions for this reaction to increase the selectivity and yield of reaction. The sulfonic acid functionalized mesoporous materials were reported to be efficient catalysts for acid catalyzed reactions [6]. Hybrid mesoporous SBA-15-Pr-SO3H with organic propyl groups in the pores of the SiO2 mesostructue would make the materials hydrothermal stable and hydrophobic and thus provide the materials with improved catalytic properties during applications for organic small molecules [7]. For these reasons and in our continuing interest in the development of environmental friendly protocols and one-pot multi-component reactions, we report herein our results for the synthesis of tri- and tetra-substituted imidazoles using easy producible and affordable SBA-15-Pr-SO3H as an suitable, efficient and green catalyst for the multicomponent condensation of an benzil and amines with aldehyde, without any solvent, salts and additives with excellent yields (Scheme 1).