Polycyclic aromatic hydrocarbons by ring-closing metathesis.

A strategy for the synthesis of polycyclic aromatic hydrocarbons (PAHs) by the ring-closing olefin metathesis (RCM) of pendant olefins on a phenylene backbone has been developed. RCM of 2,4',6',2' '-tetravinyl-[1,1';3',1' ']terphenyl and 2,2',5',2' '-tetravinyl-[1,1';4',1']terphenyl affords in high yield the isomeric [a,j] and [a,h] dibenzanthracenes, respectively. In contrast with other intramolecular annulation methods, such as Friedel-Crafts acylations, this reaction is completely regioselective. Since RCM is reversible and PAHs are often thermodynamic sinks, this strategy is an effective and general method for the preparation of PAHs. Density functional theory calculations support these results. Carbon disulfide is a suitable solvent for these reactions.