Supported gold nanoparticles as efficient and reusable heterogeneous catalyst for cycloisomerization reactions

We report the utilization of a novel catalyst for cycloisomerizations. The novel catalyst system contains gold nanoparticles supported on Al-SBA15, which was prepared by the ball-milling process. We developed a greener methodology for synthesizing spiroindolines under heterogeneous conditions, using this novel class of supported gold nanoparticles in combination with microwave irradiation. The catalyst is highly reusable and selective. Cycloisomerization reaction yields ranged from good to excellent leading to the formation of two novel classes of six- and seven-membered heterocycles, which have been unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as the solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity.