Corannulene derivatives, synthesis

Scheme 3 Synthesis of corannulene derivatives in solution phase by Method A [32, 34]...

Scheme 5 Synthesis of dibromo-substituted corannulenes derivatives by Method C [25, 39, 40]...

Preparation of 2,3-disubstituted corannulene derivatives requires an alternative synthesis (Scheme 9) [57]. 2,3-DiphenyIcorannulene (32) was generated by the Ni-catalyzed Kumada coupling of 2,3-dichlorocorannulene (19) with phenyl-magnesium bromide. Similarly, the Ni-catalyzed methylation of 19 with trimethyl-aluminum yielded 2,3-dimethylcorannulene (33), from which the bis-(bromomethyl) derivative 34 was obtained by benzyUc bromination with M-bromosuccinimide. Moreover, heating 19 in diethylene glycol monomethyl... 

Scheme 13 Synthesis of pentasubstituted corannulene derivatives liom pcmtachloiDcraannulene...

Two years later, Craig and Robinson attempted an alternative synthesis of 8 with a more symmetrical pathway starting from derivatives of fluoranthene. Cycliza-tion of fluoranthene-7,10-diacetic acid 14 was attempted to produce diketone 15, expected to enolize to the dihydroxycorannulene 16. Unfortunately, several attempts at cyclization failed, including anhydrous hydrofluoric acid, concentrated sulfuric acid, and polyphosphoric acid. Friedel-Crafts cyclization of the corresponding acid chloride of 14 with aluminum or stannic chloride was similarly unsuccessful. However, although Craig and Robinson were not successful, they developed a convenient synthesis of 7,10-disubstituted fluoranthenes which turned out later to be of premium importance in a new, successful synthesis of corannulene. 

An alternative synthesis of corannulene, also involving a pyrolysis, was reported by Siegel and co-workers (Scheme 4), The tetrabromide may be directly pyro-lyzed to corannulene, or it may be converted to a bis-sulfone where extrusion of SO2 produces a mixture of 8 along with its di- and tetrahydro derivatives, and 5,6-dimethy 1-benzo [g/ir] fluoranthene. 

In Chapter 2, Matsuo and Nakamura describe the synthetic developments of a subgroup of bowl-shaped it-conjugated corannulenes and expand the topic to the discussion of the synthesis of a novel class of organic fluorophores derived from C60, hoop-shaped condensed aromatic compounds. They are made by selective removal of ten sp2 carbon centers out of conjugation from the north and south pole regions of C60. The resulting 40-jr-electron [lOjcyclophenacenes excised... 

Transition-metal complex of n bowls have attracted much attention [12, 34, 35]. Controlled positioning of metal centers inside the bowls is expected to provide a direct route to the inclusion complexes of fiillerenes and nanotubes. On the other hand, the coordination of metal centers to the outside of the bowls should permit applications in the field of surface activation and functionalization of fiiUerenes and nanotubes. To date, some n bowl (mainly corannulene or its derivatives) complexes with several coordination modes have been synthesized [12, 34, 35]. In addition to the conventional liquid phase synthesis, a microscale gas-phase coordination method was introduced [36] to prepare and/or jj -binding complexes, which is based on co-deposition of volatile complementary building units such as Rh2(02CCF3)4, Ru2(02C(3,5-CF3)2C H3)2(C0)5, and Ru2(02CCF3)2(C0)4 under reduced pressure. 

The synthesis of a plethora of sym-pentakis substituted corannulenes was recently published by Siegel et al. [37]. The authors introduced various substituents, including sp (37), sp (38) and sp hybridized carbon atoms (39) directly connected to 1 as well as some -SR (40) and -OR (41) derivatives [37]. The UV/vis absorption and emission properties of the derivatives were also studied, as well as the inversion barriers of some of the derivatives vide infra). The Stokes shifts were found to be in the range of 130 nm in all derivatives investigated [37]. 

The corannulenes are the simplest examples of compounds with a curved surface. They include fluoranthenes that are important synthetic intermediates in the construction of corannulenes and their derivatives. Indenofluoranthenes have a curvature of a higher order due to the inclusion of two 5-membered rings. Methods for the synthesis of fluoranthenes from naphthalene and indenocorannulenes from corannulenes offer approaches to the formation of high-order spherical and tubular structures. 

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