Peroxydicarbonate-mediated oxidation of N-(ortho-aryloxyphenyl) and N-(ortho-arylaminophenyl)aldimines

Article abstract of DOI:10.1016/0040-4020(95)00769-5

Imidoyl radicals 5, obtained from imines 1 by hydrogen abstraction with di-iso-propyl peroxydicarbonate (DPDC), give dibenzoxazepines through 7-membered ring closure. A competitive 6-membered cyclisation leads to intermediate spirocyclohexadienyl radicals that rearrange to aryloxy radicals; this process entails a novel 1,5-aryl radical translocation from an oxygen to a carbon atom and leads to benzophenones, benzoxazoles, and biphenyls. The possibility that the oxazepines arise from rearrangement of the 6-membered-ring-closure intermediates is discussed. With imine 1e, 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 linked to the two oxygen atoms. The 1,5-aryl migration can also be observed with imidoyl radicals generated by radical addition to 2-phenoxyisocyanobenzene. In contrast, the reactions of imines 2 with DPDC do not afford imidoyl radicals, as abstraction of the iminic hydrogen is slower than oxidation of the methyl group: this process entails the formation of carbamoyl radicals, which cyclise onto the carbonitrogen double bond, furnishing quinoxalinone derivatives, or loose carbon monoxide to yield benzimidazoles through ring closure of aminyl radicals. A novel cyclisation of a nitrogen-centred radical onto a formamido group could account for the formation of a benzimidazolinone derivative.