Supported gold nanoparticles as an efficient reusable and green 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, ensuring that the majority of the metal is deposited on the surface and not inside the pores of the support. 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 are unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity