Retro-cyclopropanation reactions fullerene derivatives

This chapter presents an up-to-date account of the redox properties of the pristine fullerenes and a large number of their derivatives as revealed by electrochemical studies in solution. The description here is as exhaustive as possible, although not completely comprehensive due to the large number of reports on the subject that have appeared over the years. A section on electrosynthesis of fullerene derivatives is included, with special emphasis on the retro-cyclopropanation reaction, a reaction that has led to the formation of novel derivatives as well as... 

At this point, it is important to indicate that a very large number of C-bridged cyclopropanated fullerene derivatives undergo irreversible reduction processes leading to the removal of the addend and recovery of the pristine parent fullerene. The process has been advantageously used in electrosynthetic procedures, and thus a separate section covering the electrochemically induced retro-cyclopropanation reaction is presented later in this chapter (see Sect. 6.1.5.2). A number of other C-bridged cyclopropanated derivatives will be discussed there. 

Two of the three pairs of diastereomers reduce at potentials more positive than those of the parent [76] fullerene, while the other pair is actually more difficult to reduce. Interestingly, in contrast with similar Ceo and C70 derivatives, the di-and trianions of these C76 monoadducts are much more chemically stable. In fact, the retro-cyclopropanation reaction (see Sect. 6.1.5.2 below), which removes the malonate addend, occurs in very low yields... 

The usefulness of the retro-cyclopropanation reaction is even more remarkable than previously anticipated. It was questioned whether this reaction allowed the selective removal of a Bingel-type addend while leaving addends of a different type unaffected. A variety of mixed bis-adducts such as those shown in Fig. 29, were prepared, all of which contained a bis(ethoxycarbonyl)methano group [182]. In all cases, CPE led to the selective removal of the Bingel addend in over 60% yield, while the other one was retained, confirming that the reaction may be used in a synthetic protection-deprotection protocol to prepare novel fullerene derivatives. 

In this section we present the use of the retro-cyclopropanation reactions for the synthesis of fullerene derivatives which are not available by other routes, and for the isolation of isomers and enantiomers of the higher fullerenes. 

The reverse reaction to the Bingel cyclopropanation - the so-called retro-Bingel reaction - was developed by Diederich, Echegoyen and coworkers [70] and opens up the possibility to remove the Bingel-addend completely. This removal was successfully done with Cjq malonates [70, 71], dialkoxyphosphorylmethano[60]-fullerene [72], methano[60]fullerenyl amino acid derivatives [73] and also with... 

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