ENOL RADICAL CATIONS IN SOLUTION - 13 - FIRST EXAMPLE OF A RADICAL DICATION REARRANGEMENT - ONE-ELECTRON OXIDATION OF DIHYDROBENZOFURANYL CATIONS LEADS TO DRASTIC RATE ENHANCEMENT IN THE OXIDATIVE BENZOFURAN FORMATION FROM ENOLS

The synthesis and electrochemical investigation of six stable, simple enols E1-E6 are reported that are characterized by electron-releasing substituents in the alpha-position. Oxidative benzofuran formation fro m these enols is unusually slow because a key intermediate in the reac tion, the dihydrobenzofuranyl cation X+, is substantially stabilized v s rearrangement by the attached electron-releasing substituents. The p ersistent cations X+ were characterized by H-1 NMR and cyclic voltamme try, and the kinetics of their rearrangement was followed by UV/vis. N otably, upon one-electron oxidation of X+ to the radical dication, the formation of the benzofurans B was markedly accelerated by a factor o f >10(6).