Gold Supported on Silica Catalyzes the Aerobic Oxidation of N,N-Disubstituted Hydroxylamines to Nitrones

A new method for the preparation of nitrones through the aerobic oxidation of the corresponding N,N-disubstituted hydroxylamines has been developed by exploring a new catalytic reactivity of gold supported on silica. The oxidation occurs under very mild conditions (flux of air, methanol or water, room temperature). The oxidation of a range of highly functionalized hydroxylamines with complete conversions and excellent yields of nitrones illustrates the selectivity, efficiency, and reliability of this practical method. The oxidation was shown to take place chemoselectively in competition experiments with benzyl alcohol and dibutylamine.