Tandem addition reactions of dialkoxyanthracenes with C60.: Thermal vs. electrochemical stability of Diels-Alder adducts

In order to improve the ability to follow the events occurring in retro-cyclopropanation reactions, new methanofullerenes that incorporate fluorescent anthracene malonates were prepared using the Bingel cyclopropanation reaction. Since anthracene groups undergo thermal [4 + 2] cycloadditions with the [6,6] bonds of C-60, the formation of the corresponding side products, along with the Bingel adducts, was confirmed by H-1 NMR, HPLC, and cyclic voltammetric studies. When the anthracene malonates were reacted with C-60 following a Diels-Alder protocol, the corresponding monoadducts were obtained. The mono-Diels-Alder derivative 5 was investigated under controlled potential electrolysis conditions and does not exhibit decomposition when approximately two electrons per C-60 derivative were transferred. In contrast, upon heating to temperatures of 50 to 90 degreesC the monoadducts 5 and 6 decomposed to [60]fullerene and the corresponding anthracenes.