tert-Butyl Hydroperoxide and Tetrabutylammonium Iodide-Promoted Free Radical Cyclization of α-Azido-N-arylamides

The oxidizing system of tert-butyl hydroperoxide (TBHP) and tetrabutylammonium iodide (TBAI) is capable of engendering alpha-(aminocarbonyl)iminyl radicals from alpha-azido-N-phenylacetamides. These iminyl radicals preferably undergo intramolecular attack on the benzene ring to give azaspirocyclohexadienyl radicals, which are readily captured by O-2 under an oxygen atmosphere to yield azaspirocyclohexadienones. In the absence of oxygen, the reaction will afford quinoxalin-2-one products. The generation of alpha-(aminocarbonyl) iminyl radicals is proposed to involve an initial deprotonation and denitrogenation, and subsequent oxidation of thus formed imine intermediates by tert-butoxy radical and/or tert-butyl peroxyl radical.