Gold-coated iron oxide core–shell nanostructures for the oxidation of indoles and the synthesis of uracil-derived spirooxindoles

Abstract

Encapsulation of iron oxide (Fe₃O₄)-based nanoparticles (NPs) with Au NPs holds a promising scope for catalysis, which overcomes the hindrance of the inherent hydrophilic surface of iron species and facilitates the easy separation of colloidal Au NPs. As such, iron oxide-based NPs were encapsulated by Au NPs to form core–shell structures (Fe₃O₄/Au NPs) followed by further immobilization on in situ synthesized reduced graphene oxide (rGO) to yield Fe₃O₄/Au NPs–rGO for increased stability. Fe₃O₄/Au NPs–rGO was evaluated for the oxidation of NH-free indoles to synthesize isatins, potential precursors of SARS-CoV-2 protease inhibitors. Furthermore, the application of isatin was explored with the Fe₃O₄/Au NPs–rGO catalysed synthesis of uracil-based spirooxindoles (potential precursors of anti-cancer compounds) via mild reaction conditions and short reaction times with high yields.