Merging a Negatively Curved Nanographene and a Carbon Nanoring

Two
molecular nanocarbons result from merging a negatively curved nanographene
and a carbon nanoring in two constitutional isomers of D2 and C2v symmetry, respectively. They were synthesized by attachment of C-shaped
paraphenylene precursors to 2,11,18,27-tetrabromooctabenzo[8]circulene
and the subsequent intramolecular Yamamoto coupling and reductive
aromatization reactions. The flexible nature of octabenzo[8]circulene
enabled two different ways of connection in the Yamamoto coupling
reactions, leading to the two constitutional isomers. The D2 isomer is shaped like a figure eight, as revealed
by X-ray crystallography, and is resolved into two enantiomers by
chiral HPLC. The synthesis of the C2v isomer is regarded as a further step toward precision
synthesis of carbon schwarzites through a bottom-up approach.