Selective electrolytic removal of bis(alkoxycarbonyl)methano addends from C-60 bis-adducts and electrochemical stability of C-70 derivatives

The novel mixed bis-adducts of C-60, (+/-)-4-(+/-)-8 and 9, with a bis(etho xycarbonyl)methano addend (Bingel addend) and a second addend ([1,2]benzeno . but[2]eno, methanimino-methano. or diarylmethano) bridging 6.6-closed bon ds of the carbon sphere were synthesized in two-step reactions. Each bis-ad duct was exhaustively electrolyzed at the potential of the second fullerene -centered reduction step, resulting in the selective removal of the Bingel addend (retro-Bingel reaction) to produce the corresponding mono-ad-ducts, which were isolated in yields of over 60%, These results open up the possib ility of using the Bingel addend as a temporary protecting and directing gr oup in the construction of multiple adducts of C-60 with unusual addition p atterns. The Bingel-type mono-adduct of C-70 10 and the constitutionally is omeric bis-adducts 11, (+/-)-12, and (+/-)-13 were also included in this in vestigation. A large difference in the electrochemical behavior between Ci, bis-adducts and the corresponding C-60 derivatives was observed. Thus, the intramolecular "walk-on-the-sphere" isomerization which occurs readily wit h Bingel-type bis-adducts of C-60 under the conditions of two-electron cont rolled potential electrolysis (CPE) is only a minor reaction pathway in the series of C-70 derivatives The latter preferentially undergo retro-Bingel reaction.