Reactivity of nitroso oxides: Effect of polar substituents and reaction mechanism

The structure and reactivity of nitroso oxide intermediates has been studied by trapping and tracer experiments in the photooxidation of substituted phenyl azides, O-Transfers with p-methoxyphenyl nitroso oxide were efficient and showed the reactivity order of PhN=O > Ph(2)S > Ph(2)SO > PhH. Sulfides and sulfoxides were oxidized electrophilically and the partial rate factor for the hydroxylation of benzenes afforded a negative rho-value of -1.40 (sigma(+)). In the case of the p-nitrophenyl isomer, the radical reactivity was much more significant as exemplified in the hydrogen abstraction from toluene. Both isomers behave as electrophilic radicals as shown by the relative rates of hydrogen abstraction from aliphatic C-H bonds, i.e., 1 degrees:2 degrees:3 degrees = 1:7:50-60. An O-18-tracer study revealed that the intramolecular cyclization of aryl nitroso oxides is competitive with intermolecular O-transfers.