Synthesis and Structure of a Propeller-Shaped Polycyclic Aromatic Hydrocarbon Containing Seven-Membered Rings.

The synthesis and structure of a C3-symmetric propeller-shaped polycyclic aromatic hydrocarbon that bears three seven-membered rings is reported. The synthesis was accomplished in three steps from benzo[ c]naphtho[2,1- p]chrysene, including a Pd-catalyzed intramolecular C-H arylation for the formation of the seven-membered rings. The combination of the helicities ( P/ M) of the three seven-membered-ring moieties and three [4]helicene moieties affords 24 possible conformers, and two relatively stable conformations were observed by 1H NMR spectroscopy.