Synthesis of a Basket-Shaped C₅₆H₃₈ Hydrocarbon as a Precursor toward an End-Cap Template for Carbon [6,6]Nanotubes

A basket-shaped C56H38 hydrocarbon (3) possessing a 30-carbon difluorenonaphthacenyl core that can be mapped onto the surface of C78 was synthesized from 4-bromo-1-indanone. The first stage of the synthesis involved the preparation of tetraketone 10 as a key intermediate. The use of cascade cyclization reactions of benzannulated enyne−allenes as key features in the next stage of the synthetic sequence provides an efficient route to 3 from 4-bromo-1-indanone in 12 steps. The all-cis relationship among the methyl groups and the methine hydrogens causes the two benzofluorenyl units in 3 to be in an essentially perpendicular orientation to each other. Hydrocarbon 3 and its derivatives could serve as attractive precursors leading to a geodesic C68H26 end-cap template for carbon [6,6]nanotubes.