The Bingel Macrocyclization

7 Regio- and Stereoselec tive Multiple Functionalization of Fullerenes 

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Figure 6 Representative examples of C6o bis-adducts directly produced by the Bingel macrocyclization reaction.

Scheme 7-6 General protocols for the Bingel macrocyclization reaction [25,59,60],...

Scheme 7-8 Examples of Cgg bis-adducts directly produced by the Bingel macrocyclization reaction (Scheme 7-6). For each compound, the molecular symmetry and the preparation yield are given.

The Bingel macrocyclization has been increasingly exploited in the construction of molecular building blocks for supramolecular systems. For this purpose, cis-2 bis-adducts, such as 43 with a m-xylylene tether (Scheme 7-8), have been particularly useful. Thus, bis-adducts 55 [70], a fullerene-glycodendron conjugate, and 56 [71] were shown to form stable Langmuir monolayers at the air-water interface (Scheme 7-9). 

Scheme 7-9 Examples of functional supramolecular systems containing C q cis-2 bis-adducts prepared by the Bingel macrocyclization.

Scheme 7-10 Extensions of the Bingel macrocyclization preparation of a higher adduct of Cgy [25] and use of tethered bis(jHceto esters) instead of tethered bismalonates [74]. THP=3,4,5, tetrahydro-2//-pyran-2-yl.

Since cis-3, trans-3, and trans-2 bis-adducts of 50 with identical addends are chiral as a result of inherently chiral functionalization patterns [10, 44-46], it was of interest to explore whether Bingel macrocyclizations with bismalonates bridged by non-racemic tethers would provide an enantioselective synthesis of these compounds. An overall enantioselective synthesis of optically active Cgg bis-adducts had been achieved previously by asymmetric Sharpless bis-osmylation [77] however, this sequential bis-func-tionalization lacks the regioselectivity of the Bingel macrocyclization, and therefore requires tedious regioisomer separations. 

The Bingel macrocyclization is not completely regioselective in each case [25, 59]. As an example, the use of a tether derived from l,10-phenanthroline-2,9-dimethanol yielded both e bis-adduct ( )-46 and trans-A bis-adduct 47. 

One of the most convenient of these tether-directed functionalization strategies exploits the macrocyclization of C60 with bismalonate derivatives in a double Bingel reaction.156,571 With the exception of the cis-1 bisaddition product, all possible bisaddition patterns have been obtained by this macrocyclization reaction (Figure 13). As a general... 

Possibly the simplest and most versatile method for the preparation of covalent bis-adducts of C(,o with high regio- and diastereoselectivity is the macrocyclization between C(,o and bismalonate derivatives in a double Bingel reaction [7,8,26,27], In theory, each macrocyclic regio-isomer could form as a mixture of diastereomers, depending on how the EtOCO residues at the two methano bridge C-atoms are oriented with respect to each other (in-in, in-out,... 

With the bis-malonate 56 containing a vra-disubstituted DB18C6 tether, the regioselectivity of the macrocyclization of C70 via double Bingel cyclopropanation... 

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

Planar chirality was finally combined with the achiral cis-2 addition pattern in a tethered Bingel type bis-adduct including a trans-configured ethene unit as planar chiral element in the macrocyclic bridge.118... 

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. 

Photoinduced ET was studied in fullerene bisadducts synthesized throngh a Bingel reaction bearing different kinds of macrocycles in a parachute-like shape architecture. The double addition to Cgo imposes geometrical restrictions that set the macrocycle and the fullerene moieties in spatial proximity and affects the ET as well as the CR processes. 

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