Ultrasonically-mediated one-pot synthesis of substituted imidazoles via sulfamic acid functionalized hollow magnetically retrievable solid-acid catalyst

Abstract In this work, we report the synthesis of functionalized hollow magnetite spheres (HMS) which were synthesized through gas-bubble assisted Ostwald ripening approach and post-functionalized with sulfamic acid groups. The fabricated material was used as an efficient solid-acid catalyst for one-pot three-component synthesis of medicinally important tri-substituted imidazoles under ultrasonic irradiation. Some of the striking features of the present protocol over existing routes are environmentally benign synthesis, milder reaction conditions, excellent yields, high selectivity, short reaction times, use of ultrasound as green energy source, less waste generation and effortless magnetic recovery and recycling of the catalyst. Further, the synthesized magnetite spheres extend the scope of ‘double functionalization’, i.e., the acidic groups can be immobilized on both internal and external surfaces which provides high acid loading as compared to previously reported solid supports.