Aromatic π-Systems More Curved Than C₆₀. The Complete Family of All Indenocorannulenes Synthesized by Iterative Microwave-Assisted Intramolecular Arylations

Syntheses and X-ray crystal structures are reported for all seven members of the indenocorannulene family, comprising indenocorannulene, both isomers of diindenocorannulene, both isomers of triindenocorannulene, tetraindenocorannulene, and pentaindenocorannulene. With each additional indenoannulation, the pyramidalization of the trigonal carbon atoms at the hub of the corannulene increases. Five of the seven indenocorannulenes contain carbon atoms at the hub that are actually more pyramidalized than the carbon atoms of C60. This work demonstrates, for the first time, that extended π-systems with curvatures exceeding those of the most curved stable fullerenes and carbon nanotubes can be prepared by ordinary laboratory methods in solution, without recourse to high-temperature gas phase methods, such as flash vacuum pyrolysis. This proof of principle presages the days when scientists will be able to synthesize isomerically pure fullerenes and single-chirality nanotubes by well-understood, controlled chemical methods. Pentaindenocorannulene, itself, represents an attractive precursor to the C5v end-cap of an all-carbon, single-walled, “armchair” [5,5]nanotube.