Intramolecular addition of oxyradicals to benzene rings: A DFT study

The reactivity of a series of oxyradicals related to the triplet state of β-phenylpropiophenone was investigated by density functional theory. Analysis of the potential energy hypersurfaces indicates that radical addition to the β-phenyl ring should occur with a smaller barrier than intramolecular hydrogen abstraction from the benzylic position, although the latter reaction is far more exothermic. Addition can occur in ipso- and ortho-position of the β-phenyl ring, with ortho addition being slightly more favourable. As both addition reactions are predicted to be mildly exothermic and exergonic, intermolecular trapping of the resulting cyclohexadienyl- type radicals should be feasible.