Synthesis, Characterization, and Application of a Novel Polystyrene-Supported Brønsted-Acidic Ionic Liquid as an...

Herein, we report a novel synthesis of the polymer-supported Brønsted-acidic ionic liquidPS-[(SO₃H)⁴C₄Im]-[OTf]as an efficient and recyclable heterogeneous catalyst for the Groebke-Blackburn-Bienaymé (GBB) multicomponent reaction. The catalyst was synthesized from Merrifield resin (polystyrene) and fully characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Its catalytic activity was then evaluated in GBB model reactions, with the optimal conditions determined using 50 mg mmol^-1 of PS-[(SO₃H)⁴C₄Im]-[OTf] in ethanol as solvent under microwave heating at 150 °C for 1 h. A diverse library of imidazo-fused heterocycles (e.g., imidazo-[1,2-a]-pyridines, imidazo-[2,1-b]-thiazoles, and benzo-[d]-imidazo-[2,1-b]-thiazoles) was synthesized using the optimized conditions and the corresponding products were obtained in moderate to excellent yields (34-91%), depending on the starting aminoazole. Furthermore, the heterogeneous catalyst could be easily recovered by filtration after each reaction cycle and reused for up to six consecutive cycles with no significant loss of integrity as well as catalytic activity (average yield 86 ± 3.5%). These results demonstrated the potential of this polymer-supported Brønsted-acidic ionic liquid as a sustainable catalyst for acid-catalyzed multicomponent reactions applied to the synthesis of nitrogen-based heterocycles of interest in Medicinal Chemistry.