Bingel intramolecular

The stabilization of reaction intermediates RCjq and RC q to form dihydrofullerene derivatives can also be achieved by intramolecular nucleophilic substitutions (SjJ), if R contains a leaving group. As shown by Bingel [31], the generation of a carbon nucleophile by deprotonation of a-halo esters or a-halo ketones leads to a clean cyclopropanation of Cjq. 

The electrochemical properties of all these bis-adducts have been studied in reasonable detail, using either cyclic voltammetry (CV) or controlled potential electrolysis (CPE) [8], Reductive electrolysis of ester-containing methanofullerenes results in the removal of the adducts in a versatile and useful reaction, initially called the retro-Bingel reaction (Figure 1). Additional work resulted in the discovery of an intramolecular electrochemically induced isomerization of C6o-bis-adducts. Exhaustive reduction with one electron per molecule resulted in seven regio-isomers regardless of which pure bis-adduct regioisomer was electrolyzed. Recently, it has been observed that, in addition to the malonates, electrochemical reduction of other methano-adducts can also lead to removal of the addends,... 

A reaction fulfilling this requirement is the Bingel addition [130], a methano-fullerene synthesis in which the attack of 2-bromomalonate carbanions on the fullerene is followed by intramolecular halide displacement. In the mono-func-tionalization of C7o,it shows a high preference for the C(l)-C(2) bond [54,130]. This can be rationalized by the preference of the -hybridized carbanionic cen-... 

In 2007 two independent contributions made by Cordova and co-workers [14] and by W. Wang and co-workers [15] reported a simple and highly stereoselective cyclopropanation via the reaction of enals (15) and 2-bromomalonates (18). Catalyst VII allowed, based on a Michael addition and subsequent intramolecular a-alkylation (i.e., a Bingel-Hirsch reaction) of the enamine intermediate, the production of the cyclopropane motif 17 (Scheme 10.9, B). 

The most used nucleophilic synthesis reaction to form fuUerenes is cyclopropanation. The original method was developed by Bingel, and it employs the generation of a carbon nucleophile starting from a-halo esters in the presence of a base (such as NaH), and the subsequent addition to After the addition of the anions of a-halo ester, an intramolecular substitution of the halide takes place with the intermediate fullerene anion, giving the corresponding methanofullerene derivative (Scheme 2.1e). Further modification of this method consist of preparing the a-halomalonate in situ. 

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