Oxidation of N,N-Disubstituted Hydroxylamines to Nitrone with Hydrogen Peroxide Catalyzed by Polymer-Supported Methylrhenium Trioxide Systems

Poly(4-vinylpyridine)/methylrhenium trioxide (MTO) compounds IIII and microencapsulated polystyrene/MTO systems IVV are efficient catalysts for the oxidation of secondary hydroxylamines to the corresponding nitrones with H2O2. Complete conversions of substrates and quantitative yields of products are obtained under environmentally friendly experimental conditions and with the use of simple work-up procedures. Symmetrically substituted hydroxylamines, and non-symmetrical 3-substituted and 2-substituted hydroxypyrrolidines, precursors of nitrones applied in the synthesis of alkaloids and biologically active congeners, have been considered as substrates. The heterogeneous catalysts are stable under the reaction conditions and can be recovered and recycled for at least five times without any appreciable loss in efficiency.