Methanofullerenes syntheses

Further possibilities for methanofullerene syntheses were found by Nakamura s group (Tokuyama et al., 1993) and by Rubin s group (An et al., 1994 Anderson et... 

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

An alternative synthetic approach, first developed by Bingel225 allowed the efficient nucleophilic cyclopropanation of fullerenes via their reaction with bromomalonate derivatives in the presence of base. This approach, the most reliable method for the synthesis of functionalized methanofullerenes, combined the advantages of mild... 

Gubskaya VP, Berezhnaya LS, Gubaidullin AT, Faingold II, Kotelnikova RA, Konovalova NP, Morozov VI, Litvinov IA, Nuretdinov IA (2007) Synthesis, structure and biological activity of nitroxide malonate methanofullerenes. Org. Biomol. Chem. 5 976-981. 

As well as the Bingel reaction and its modifications some more reactions that involve the addition-elimination mechanism have been discovered. 1,2-Methano-[60]fullerenes are obtainable in good yields by reaction with phosphorus- [44] or sulfur-ylides [45,46] or by fluorine-ion-mediated reaction with silylated nucleophiles [47]. The reaction with ylides requires stabilized sulfur or phosphorus ylides (Scheme 3.9). As well as representing a new route to l,2-methano[60]fullerenes, the synthesis of methanofullerenes with a formyl group at the bridgehead-carbon is possible. This formyl-group can be easily transformed into imines with various aromatic amines. 

The reaction of Cjq with silylated nucleophiles [47] requires compounds such as silyl ketene acetals, silylketene thioacetals or silyl enol ethers. It proceeds smoothly and in good yields in the presence of fluoride ions (KF/18-crown-6) (Scheme 3.10). The advantage of the latter synthesis is the realization of the cyclopropanation under nearly neutral conditions, which complements the basic conditions that are mandatory for Bingel reactions. Reaction with similar silyl ketene acetals under photochemical conditions and without the use of F does not lead to methanofullerenes but to dihydrofullerene acetate [48]. 

The synthesis of methanofullerenes 955 was achieved starting from / -tosylhydrazones 954 and Cso under basic conditions (toluene, 70 °C). Tosylhydrazones 954 were prepared from the respective aldehydes 953 and />-toluene sulfonylhydrazide (Scheme 146) <2000CC113>. 

The need to prepare fullerene derivatives for possible applications to medicine and material sciences resulted in the development of novel synthetic methods for the functionalization of Cso. R. Pellicciari et al. reacted Ceo with carboalkoxycarbenoids generated by the Rh2(OAc)4-catalyzed decomposition of a-diazoester precursors. This reaction was the first example of a transition metal carbenoid reacting with a fullerene and the observed yields and product ratios were better than those obtained by previously reported methods. The reaction conditions were mild and the specificity was high for the synthesis of carboalkoxy-substituted[6,6]-methanofullerenes. When the same reaction was carried out thermally, the rearranged product (the [6,5]-open fullerene) was the major product. 

Figure 2.56 collects some exemplary reactions of Ceo with different bromoma-lonates and other applicable keto compounds. This collection shows that there is virtually no Umit to the choice of side chains, which renders the Bingel-Hirsch reaction an attractive and flexible starting point for the synthesis of fuUerene-containing materials. For example, the base-mediated conversion of a malonate and Cao into the respective methanofullerene can also be achieved. With the semiester of malonic acid instead of a malonate, the monosubstituted methanofullerene is obtained because the primary product is instantaneously decarboxylated (Figure 2.56). P-Ketoesters may also be reacted under Bingel-Hirsch conditions to give methanofuUerenes.

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. 

In general, the methanofullerenes formed by the Bingel reaction are stable and have been used widely for the synthesis of new materials. However, as a drawback, they show liability under reductive conditions. Electrochemical reduction is sufficient to induce a reverse Bingel reaction in di(alkoxycarbonyl)methanofullerenes, generating the parent fullerene and starting malonate as products. ... 

Gonzalez, S., Martin, N. and Guldi, D. M. Synthesis and properties of Bingel-type methanofullerene-it-extended-TTF diads and triads. J. Org. Chem. 68, 779-791, 2002. 

The first example was reported in 1994 by Diederich, who electropolymerized a bis(l,3-dialkyne)methanofullerene to obtain conductive films [51]. Nowadays, several research groups are engaged in the synthesis and study of D-C polymers, especially in the search for more efficient organic photovoltaic solar devices [52]. 

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