PEROXYDICARBONATE-MEDIATED OXIDATION OF N-(ORTHO-ARYLOXYPHENYL) AND N-(ORTHO-ARYLAMINOPHENYL)ALDIMINES

Imidoyl radicals 5, obtained from imines 1 by hydrogen abstraction wit h di-iso-propyl peroxydicarbonate (DPDC), give dibenzoxazepines throug h 7-membered ring closure. A competitive 6-membered cyclisation leads to intermediate spirocyclohexadienyl radicals that rearrange to arylox y radicals; this process entails a novel 1,5-aryl radical translocatio n from an oxygen to a carbon atom and leads to benzophenones,benzoxazo les, and biphenyls. The possibility that the oxazepines arise from rea rrangement of the 6-membered-ring-closure intermediates is discussed W ith imine le, the formation of 5e occurs to a minor extent owing to a side-reaction of the iso-propoxycarbonyloxy radicals, which give rise to an intermolecular aromatic ipso-substitution on the benzenic ring l inked to the two oxygen atoms. The 1,5-aryl migration can also be obse rved with imidoyl radicals generated by radical addition to 2-phenoxyi socyanobenzene. In contrast, the reactions of imines 2 with DPDC do no t afford imidoyl radicals, as abstraction of the iminic hydrogen is sl ower than oxidation of the methyl group: this process entails the form ation of carbamoyl radicals, which cyclise onto the carbon-nitrogen do uble bond, furnishing quinoxalinone derivatives, or loose carbon monox ide to yield benzimidazoles through ring closure of aminyl radicals. A novel cyclisation of a nitrogen-centred radical onto a formamido grou p could account for the formation of a benzimidazolinone derivative.