Some intramolecular reactions of ortho-substituted aryl radicals

Abstract

ortho-Substituted aryl radicals have been generated by reduction of arenediazonium salts in aqueous solution by use of a flow cell. The e.s.r. spectra indicate that radicals containing olefinic bonds in the 5,6- or 6,7-positions with respect to the radical centre undergo rapid cyclization by addition to the 5- and 6-positions respectively to give the thermodynamically less stable products. No evidence was obtained for addition to the remote termini of the double bonds. The direction of cyclization is not determined primarily by the case of approach of the radical centre to the olefinic carbon atoms. Aryl radicals containing saturated ortho-substituents undergo rearrangement by 1,5-intramolecular hydrogen atom transfer. The conclusions based on e.s.r. spectroscopic studies have been supported by the isolation of rearranged products from the reduction of suitable arenediazonium salts.