Electrochemical studies of seven regioisomers of tris[di(ethoxycarbonyl)methano][60]fullerene: Umpolung of regiochemistry in retro-bingel reactions and walk-on-the-sphere rearrangements

Seven of the possible 46 constitutional isomers of tris[di(ethoxycarbonyl)m ethano[60]fullerene have been isolated and their electrochemical properties studied in CH2Cl2. A two-electron controlled potential electrolysis of eac h of these isomers results in competing retro-Bingel and isomerization reac tions with preferential loss of one or two of the addends. PM3 and AM1 comp utational studies indicate that while the reactivity of neutral precursors is kinetically controlled, charging of the neutral species with two electro ns results in an umpolung of reactivity and introduction of thermodynamic c ontrol. Lowering the electrolysis temperature increases the proportion of i somerization, and a new tris-isomer never obtained before via synthetic met hods has been isolated.