Efficacy of Au versus Au–Pd nanoparticles towards synthesis of spirooxindoles via multicomponent reaction

The catalytic efficacy of monometallic (Pd NPs) vs bimetallic nanocatalyst (Au NPs and Pd NPs supported on rGO) towards the one-pot synthesis of spirooxindole derivatives has been compared under mild reaction conditions. The multicomponent reaction comprised of reaction of substituted isatins, malononitrile, and 1,3-dicarbonyl compounds to synthesise series of diverse spirooxindoles. The nano-Au–Pd@rGO catalyst showed enhanced catalytic activity in the synthesis of spirooxindoles when compared to that of the monometallic nano-Pd/rGO catalyst which may be indicative of potential synergistic effect in the bimetallic catalyst viz Au and Pd NPs facilitating the accelerated synthesis of spirooxindoles in excellent yields. This methodology has the advantages of utilisation of non-toxic solvent, higher product yields, and lower reaction times at room temperature. Also, higher yields for spirooxindoles in case of substituted carbonyl compounds were observed, an indicative of the gem-dialkyl effect responsible to favour higher yields for spirooxindoles synthesised with di-methyl substituted cyclohexan-diones with respect to the unsubstituted ones for both catalytic systems.