The Helicenes, Radialenes, Fulvalenes, and Circulenes

A resurgence in helicene chemistry occurred in 1956 when Newman and Lednicer reported production of phenanthro[3,4-cjphenanthrene or hexahelicene 98, which displayed the stereotypical chirality resultant from steric overcrowding [80j. The 

Pentafiilvalene and heptafulvalene 109, the first symmetrical fiilvalenes, were iso- 

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 Pd atalyzed aromatization 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. 

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