Polycyclic fullerene preparation

This method has been applied to the synthesis of various polycyclic aromatic compounds [91]. Among the interesting applications are lactone formation in the preparation of natural products having biaryl skeletons (Eq. 42) [87] and double cyclization leading to spirocyclic compounds (Eq. 43) [92] and a fullerene fragment (Eq.44) [93]. 

The first pure fullerene derivative to be prepared was C5o(0s04)(4-t-butylpyridine)2. The X-ray crystal structure of this compound provided direct evidence that the proposed structure for C o was correct. Osmium tetroxide, a powerful oxidizing agent, can add across the double bonds of many compounds, including polycyclic aromatic hydrocarbons. When OSO4 was reacted with C50 and 4-ferf-butylpyridine, 1 1 and 2 1 adducts were formed. The 1 1 adduct has been characterized by X-ray crystallography, and has the structure shown in Figure 13.37. 

The existence of fullerenes, consisting of sp -hybridized carbon networks of six-and five-membered rings, renewed an interest in the chemistry and physics of carbon-rich polycyclic aromatic hydrocarbons (PAHs) in general, and especially in the subclass of PAHs that have become known as fullerene fragments or bucky-bowls. The latter curved-surface PAHs have carbon frameworks that can be identified on the buckminsterfiillerene (Ceo) surface. The simplest example is corannu-lene and it has been known for decades all of the other known buckybowls have been prepared since the early 1990s. 

Two intramolecular substitutional arylation reactions are catalyzed by Pd(0) and lead to the spherical polyaromatic hydrocarbon 3.616. X-ray diffraction study of 3.616 showed significant distortions in the structure. Such bowl-shaped polycyclic aromatic hydrocarbons are the building blocks for preparing fullerene structures [162, 291]. The first syntheses of the fullerene precursors were carried out by vacuum pyrolysis. Corannulene 3.617, diindeno[l,2,3,4-d /g l, 2, 3, 4 -mnop]chrysene 3.618, and semibuckminsterfullerene 3.619 were obtained, which creates a basis for the development of the synthesis of Cgo molecules (Figure 3.5) [300, 162]. 

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