Chemoselective Reductive Heterocyclization by Controlling the Binomial Architecture of Metal Particles and Acid−Base Properties of the Support

Abstract

2,1-Benzisoxazoles have been selectively synthesized through reductive heterocyclization of 2-nitroacylarenes using Pt-supported nanoparticles. The reaction involves a cascade process in which the first step is the reduction of the nitro group into hydroxylamine followed by heterocyclization through the nucleophilic attack of the hydroxylamine group to the carbonyl of the acyl group and further dehydration. The reaction was performed on Pt/C, Pt/TiO₂, and Pt/MgO using hydrogen as the reducing agent under mild reaction conditions. The results showed that Pt/MgO was the most active and selective catalyst. The study of the influence of the crystal size of the metal on the activity and selectivity, combined with the reaction mechanism examined by in situ Fourier transform infrared spectroscopy of the adsorbed reactant, showed that the maximum activity and selectivity to the target compound can be achieved by controlling the architecture of metal particles and acid–base properties of the support. The effect of temperature on selectivity, the stability of the Pt/MgO catalyst, and the scope of the reaction have been studied. Finally, reductive heterocyclization using different metals (Pd and Au) supported on MgO has also been performed.