Regioselectivity fullerene adducts

Silylmethylation of fullerenes can be achieved by Grignard reaction of Cjq with Me2Si(0 Pr)MgCl (Scheme 3.4). Two different types of silylmethylated 1,2-fullerene adducts are formed [8]. The use of different solvents leads either to the 1,2-product 12 or to the unprecedented 1,4-addition product 13. These compounds react easily with various alcohols or phenols, which makes silylmethylated fullerenes a versatile starting material for regioselectively defined fullerene compounds [10]. Some examples are shown in Scheme 3.4. 

F. Regioselective Self-sensitized Oxygenation of Fullerene Adducts. 857... 

TABLE 15. Regioselectivity in the self-sensitized oxygenation of fullerene adducts"... 

Self-sensitized photooxygenation of Cgo-fused cyclobutanes containing an oxidizable alkene moiety" or alkenyl-substituted fullerene adducts followed by reduction also results in the formation of allylic alcohols. Whereas in the former case formation of both the three and erythro forms of the allylic alocohols is observed, in the latter case the reaction occurs regioselectively by the preferential abstraction of an allylic hydrogen next to the fullerene group. The hydrogen atom linked to the fullerene skeleton is unreactive under the reaction conditions. 

Thioselenation of alkenes,209,210 1,3-dienes,207 and vinylcyclopropanes197 occurs by using the binary system of (PhS)2/(PhSe)2 to afford the adducts regioselectively in good yield (Table 6). Addition of a disulfide to fullerene[60] is achieved using this binary system.211... 

Beuerle F, Chronakis N, Hirsch A (2005) Regioselective synthesis and zone selective deprotection of [60]fullerene tris-adducts with an e,e,e addition pattern. Chem. Commun. 3676-3678. 

Figure 10 Regioselective one-step synthesis of topologically chiral trans-3,trans-3,trans-3 and e,e,e [60]fullerene-cyclotriveratrylene tris-adducts.

The scope of the tether-directed remote functionalization has been expanded from Cgo to the higher fullerene C70, and the described reactions are completely regioselective, featuring, in the case of C70, the kinetically disfavored addition pattern. The crown ether is a real template, since it can be readily removed by transesterification, giving a much-improved access to certain bis-adducts that are not accessible by the direct route. Cation-binding studies by CV reveal that cyclophane-type crown ethers derived from C60 and C70 form stable complexes with metal cations, and a perturbation of the fullerene reduction potentials occurs because the cation is tightly held close to the fullerene surface. This conclusion is of great importance for future developments of fullerene-based electrochemical ion sensors. 

Prior to the development of tether-directed functionalization methods, regioisomerically pure higher adducts of C50 usually were obtained by additions of transition metal complexes [31-33] or radical halogenations [34, 35]. These reactions either occur under thermodynamic control or lead to the precipitation of the least soluble derivative. Iso-merically pure higher adducts of C o sometimes are also readily isolated out of more complex product mixtures [36]. Tether-directed remote functionalization of CgQ allows the construction of fullerene derivatives with addition patterns that are difficult to obtain by thermodynamically or kinetically controlled reactions with free untethered reagents. Since the description of the first such reaction in 1994 [7], which is the subject of Section 7.3.1, an increasing variety of such regioselective functionalization protocols have... 

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