Selective Electrolytic Removal of Bis(alkoxycarbonyl)methano Addends from C60 Bis-adducts and Electrochemical Stability of C70 Derivatives

Abstract

The novel mixed bis-adducts of C60, (+/-)-4-(+/-)-8 and 9, with a bis(ethoxycarbonyl)methano addend (Bingel addend) and a second addend ([1,2]benzeno, but[2]eno, methaniminomethano, or diarylmethano) bridging 6,6-closed bonds of the carbon sphere were synthesized in two-step reactions. Each bis-adduct 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-adducts, which were isolated in yields of over 60%. These results open up the possibility of using the Bingel addend as a temporary protecting and directing group in the construction of multiple adducts of C60 with unusual addition patterns. The Bingel-type mono-adduct of C70 10 and the constitutionally isomeric bis-adducts 11, (+/-)-12, and (+/-)-13 were also included in this investigation. A large difference in the electrochemical behavior between C70 bis-adducts and the corresponding C60 derivatives was observed. Thus, the intramolecular "walk-on-the-sphere" isomerization which occurs readily with Bingel-type bis-adducts of C60 under the conditions of two-electron controlled potential electrolysis (CPE) is only a minor reaction pathway in the series of C70 derivatives. The latter preferentially undergo retro-Bingel reaction.

Selective Electrochemical Retro‐Cycloaddition Reaction of Pyrrolidinofullerenes

“…The di(alkoxycarbonyl)methano bridges can be efficiently removed from the carbon sphere by exhaustive controlled‐potential electrolysis (CPE). This electrochemical retro‐cyclopropanation reaction has been found to be of general applicability for different fullerenes and highly selective towards removal of cyclopropano addends in the presence of other types of addends 7–8. Chemical reductive methods have also been employed for efficient retro‐cyclopropanation reactions 9…”

New Reactions in Fullerene Chemistry

“…The selective removal of the bis(ethoxycarbonyl)methano addend from a similar compound (a trans-3 isomer) by electrochemical reduction proceeded with the product being formed in 63% yield. 57 The reductive CPE of 42 was carried out in dichloromethane at a potential 100 mV more negative than the second reduction peak and yielded N-methylpyrrolidino-fused C 60 37a as a major product (89% yield). This finding reveals the instability of the cyclopropane and the stability of the pyrrolidine rings under reductive conditions.…”

Design, mesomorphic properties, and supramolecular organization of [60]fullerene-containing thermotropic liquid crystals

“…11 Compound 12 was specially designed considering the electrochemical stability of fulleropyrrolidines. Indeed, while the Bingel adducts undergo retro-addition upon chemical 26 or electrochemical 27 reduction, fulleropyrrolidines lead to stable reduced species. 28 This is of interest to elaborate redox-active liquid-crystalline fullerenes.…”