Retro-cyclopropanation reactions using

In another study involving C78, a pure sample of the C2v isomer was prepared using the cyclopropanation-retro-cyclopropanation reaction sequence [44, 64]. This reaction scheme consists of a controlled potential electrolytic (CPE) reduction of a previously synthesized cyclopropane derivative of the isomer, leading to removal of the cyclopropane moiety (s), (see Sect. 6.1.5). A pure sample of the D3 isomer was obtained by high performance Kquid chromatography (HPLC) as previously described [49, 65]. The redox behavior of both isomers, in DCM at room temperature, reveals that their cathodic electrochemistry is indeed very similar (although not identical) in this solvent [44]. The first two reductions are easier for the D3 isomer by 60 and 100 mV, respectively, while the third and fourth reductions are nearly identical for the two... 

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. 

The only electrochemical study on derivatives of Cg4 describes the use of the Bingel-retro-Bingel protocol, now known as the retro-cyclopropanation reaction (see Sect. 6.1.5.2), to isolate the two major isomers of pure Cg4 by removing bis(phenylbutyl)malonate addends from mono and bis-adducts of Cg4 (see (56) in Fig. 22) [54]. CV profiles in DCM (+0.12 M TBAPFg) of two different monoadducts and four different... 

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. 

Cyclopropane derivatives of type III/64 (Scheme III/ll) have been shown to be useful starting materials for a smooth transformation to furanones [63] and thiophenes [64]. The aldol reaction of III/64 and a ketone or aldehyde yielded III/65, which forms, on desilylation, an ester diol (by a retro aldol reaction). 

The title compound also exhibits affinity for /3-dicarbonyl compounds, enabling their use as leaving groups in retro-Claisen reactions (eq 29) or cyclopropane-1,1-diester ring openings. ... 

The non-nitrogenous carbene precursor (102) was used for the photochemical generation of the carbene (103) without complications due to reactions of diazirine or diazo species. In the presence of alkenes, carbene (103) gave rise to cyclopropanes and in the absence of alkenes was proposed to undergo [1,2]-C shift to form (104), which suffered retro-Diels-Alder reaction to give a triene. 

While the double dehydrochlorination of 1,1-dichlorocyclopropane derivatives has proved successful in the preparation of a variety of cyclopropabenzenes and cyclopropa[6]naphthalenes (Table 7), the reaction fails to provide cyclopropa[a]naphthalenes, cyclopropanthracenes or higher derivatives. In these cases only substituted arenes arising from the opening of the cyclopropane ring were obtained. For the preparation of lFf-cyclopropa[<2]naphthalene a retro-Diels-Alder reaction was used (see Section 5.2.2.6.). 

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