Circulene structures

Wynberg and co-workers have prepared helicenes composed of fused thiophene and benzene units from the photocyclization of alkene precursors [134], It was shown that the effect of substituting thiophenes for benzene rings in these structures led to a blue shift of the absorption maxima. Compound 61 can be converted to the circulene structure 62 in two steps and the latter compound represents another interesting class of fused thiophene stmctures [135]. Trithiophenes with a benzene core (63) can be prepared from diacetylene-fimctionalized bithiophenes via a five-coordinate rhodium(I) intermediate by the addition of elemental sulfur [136]. A related structure (64) was reported by Pei et al. [137], along with the elaborate helicene 65. The compounds were constracted via oxidative (FeCb) cyclization reactions of 1,2-dithienyl benzene derivatives. 

Polynuclear aromatic hydrocarbons formed by the angular fusion of benzene rings may adopt either planar or nOnplanar minimum energy conformations, as demonstrated by the circulenes 8-10. [6]Circulene (coronene 9), the earliest known member of the family, prefers a planar structure of symmetry since the presence... 

Fig. 1. Structures of (a) [5]circulene, corannulene and (b) [6]circulene, coronene. Three corannulene (c) skeletons give the C60 structure (d).

Circulene 149) described recently, shows a nonplanar saddle-shaped structure in the crystal, as revealed by X-ray analysis. Wynberg et al. synthesized several heterocirculenes, which mainly show a nonplanar corrugated structure 150-155). 

The homogeneous bold connected cycles comprise the family named circu-lenesby Wynberg and Dopper [79].Corannulene (62) [4-6],coronene (63) [80], and pleidannulene (64) [81] represent the [5]-, [6]-, and [7]circulenes, respectively. A related 12-membered cycle, but not a circulene, can be seen in the structure of Kekulene (65) [82,83]. 

Since the convention for constructing the Wiswesser codes for polyhexes is understood, one can easily produce the Wiswesser code of any benzenoid by inscribing the appropriate number in each hexagon of a properly oriented polyhex. In Figs. 9.4 and 9.5, we give as examples Wiswesser codes for two structures in which the starting numeral is not unity one representing perylenes, and the other circulenes. 

FIGURE 8.7 (a) Structure of a single octathio[8]circulene molecule, (b) 3-D view of the... 

Figure 4.13 Molecular and crystal structures of corannulene and [7]circulene.

Recently, remarkable progress by several groups has been obtained in the synthesis and structural characterization of a number of [8]circulene derivatives. Notably, in 2013, Wu and coworkers [62] reported the synthesis of a series of... 

A radialene-type core also appears in the appropriate bond resonance structures of the so-called [ ]circulenes, where the central -sided ring is surrounded by n fused benzenoid rings (Figure 4.4) [107]. As the first members of the homologous series, the parent structures comprise the [3]circulene (probably too strained to be accessible by synthesis), the so far unknown [4]circulene (153), [5]circulene or corannulene (154) which is a substructure of buckminsterfullerene (Cgg), the long-known [6]circulene or coronene (155), and [7]circulene (156). 

Highly symmetric octathio[8]circulene, popularly called sulflower (sulfur + flower), the first fully heterocyclic circulene, has been synthesized recently. Molecular modeling and x-ray diffraction studies have indicated that this molecule has almost planar geometry with nearly Dgj symmetry [40], Apart from its very appealing chemical structure, this molecule has a very large surface area (56 A ), and coupled with its planar structure that ensures equal activity on either surface, it should be capable of adsorbing small molecules such as H2. Also, the planar structure (as a consequence of the presence of the S atoms) should ensure similar activity of both the top and bottom surfaces of the rings. 

FIGURE 4.12 (a) Structure for the stacked aggregate of octathio[8]circulene with the... 

Barth and Lawton s production of [5]circulene or corannulene 114 (Fig. 1.9) in 1966 [90] was a significant achievement due to the fuDerene-based, nonplanar structure of 114. The 17-step synthesis began with acenaphthene and relied on alkylation, condensation, and Pdaromatization reactions to afford the macrocycle. The following decade would see continued efforts to isolate [7]circulene IIS (Fig. 1.9) but another decade would pass before 115 was successfiilly produced [Id], Sygula and Rabideau discuss more recent work on buckybowls and fiillerene fragments in Chapter 12, whereas fullerene reactivity is outlined by Kitagawa, Mur-ata, and Komatsu in Chapter 9. 

Highly fused derivatives of cot studied this year include the as yet unknown [8]circulene (39), which is predicted to exist in a conformationally mobile saddle structure,and a series of tetraphenylenes (40) containing one, two, three, or four further bridging groups (A—D are, e.g., CH2 or CO). These were prepared from 2,2 -diIithiobiphenyls, and their chemistry has been reported. ... 

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