Polyethylene glycol methacrylate-grafted dicationic imidazolium-based ionic liquid: Heterogeneous catalyst for the synthesis of aryl-benzo[4,5]imidazo[1,2-a]pyrimidine amines under solvent-free conditions

A novel polyethylene glycol methacrylate-grafted tetra-ethylene glycol-bridged dicationic imidazolium-based ionic liquid (PEGMA-g-TEGBDIM) was prepared by grafting tetra-ethylene glycol-bridged 1-vinyl imidazolium mesylate to the surface of cross-linked polyethylene glycol methacrylate. Its structure was characterized by FT-IR, NMR, TGA, and XPS. Due to the combination of polymer-supports and flexible imidazolium linkers, it acted as a heterogeneous catalyst to exhibit excellent catalytic activity for the efficient synthesis of N-methyl-2-nitro-aryl-benzo[4,5]imidazo[1,2-a]pyrimidine amines via the multicomponent reaction of 1H-benzo[d]imidazol-2-amine (1) and (E)-N-methyl-1-(methylthio)-2-nitroethenamine (3) with a variety of aldehydes under solvent-free conditions. Moreover, PEGMA-g-TEGBDIM was easily reused and it maintained its high catalytic activity and stability even after seven reaction-cycles. This protocol perfectly obeys the features of green chemistry, including having no waste regarding side-products, being solvent-free, and having free from column chromatographic purification. (C) 2017 Elsevier Ltd. All rights reserved.