Bingel addition

Clearly, depending on the number of electrons per molecule added during CPE, either removal of the addends [170] or an isomerization reaction was attained. The former reaction was initially called the rctro-Bingd reaction [64], since it was the reverse of the Bingel addition of methano addends to Ceo [171]. The generality of the retro-Bingel and isomerization reactions has since been tested using other multiple-malonate adducts of Ceo [172,173]. In fact, the reaction has made it possible to isolate the Civ isomer of Cyg, a new Cyg bis-adduct, and new isomers of Cg4 [44, 54]. 

Scheme 1.3. General synthetic scheme for the regio- and stereoselective macrocyclization of Cgo by Bingel addition of tethered bis-malonates.

Figure 1.26. Double Bingel addition to C70 leads to an achiral top) and two inherently chiral (center and bottom) addition patterns. Combination of each of the latter with chiral ester moieties affords two diastereoisomeric pairs of enantiomers. The enantiomers of each pair were prepared separately by addition of either (R,R) or (S, -configured malonates to C70, and all stereoisomers were isolated in pure state. The black dots mark intersections of the C2-symmetry axis with the [70]fullerene spheroid. Next to the three-dimensional representations, constitution and configuration of the addition patterns are shown schematically in a Newman type projection along the Cs-axis of C70. Of the two concentric five-membered rings, the inner one corresponds to the polar pentagon closest to the viewer, and the attached vertical line represents the bond C(l)-C(2) where the first addition occurred. The functionalized bonds at the distal pole depart radially from the outer pentagon.

Scheme 7-1 (A) Position notation for bis-adducts of Cgg according to Hirsch et al. [10]. (B) Products isolated from the second Bingel addition to bis(diethoxycarbonyl)methanofullerene [C6i(COOEt)2l [10]. a) Diethyl 2-bromomalonate, NaH, toluene, 20°C.

Hirsch and co-workers subsequently discovered that the yield of hexakis-adducts such as 8 or 9 can be greatly increased and their separation from side products substantially facilitated, if 9,10-dimethylanthracene (DMA) is used as a template (Scheme 7-2) [14, 15]. Anthracene derivatives such as DMA are well known to undergo reversible Diels-Alder additions with fullerenes at ambient temperamre [16-18]. After addition to the fullerene, the template directs diethyl malonate addends in the Bingel addition tegio-selectively into e positions, ultimately yielding the hexakis-adducts with a pseudo-octahedral, all-e addition pattern. The templated activation of e 6-6 bonds (bonds between two six-membered rings) is also efficient starting from C o mono-adducts, and several examples are shown in Scheme 7-2. Thus, bis(alkynyl)methanofullerene 10 [19] reacted with diethyl 2-bromomalonate/DBU (8 equiv) and DMA (12 equiv) to provide hexakis-... 

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 1997, a [2]catenane bearing Cgo was synthesized through Stoddart s methodology,exploiting n-n interactions between aromatic moieties. " The double Bingel addition of a [34]crown-10 bismalonate to Cgo was followed by a ring-closed reaction, where the electron-deficient cyclobis-(paraquat-p-phenylene) (CBPQT +) macrocycle recognizes the electron-rich hydroquinone template. 

---