t-Butyl Biphenylation of o-Dibromoarenes: A Route to Soluble Polycyclic Aromatic Hydrocarbons

Large, soluble polycyclic aromatic hydrocarbons (PAHs) have been synthesized using Zr-mediated and Stille-type biphenylation reactions. Both the Zr and Stille methodologies have been adopted to incorporate tert-butyl substituents, permitting the direct synthesis of alkylated PAHs that are much more soluble than their unsubstituted analogues. To demonstrate the utility of these methods and the importance of solubilizing functionality, several large PAHs were synthesized and crystallographically characterized. The scope of the Zr-mediated and Stille methodologies is shown to be complementary. The Stille methodology often gives higher yields but is ineffective for the introduction of strain and failed with some polybrominated arenes. In these difficult cases, the zirconium methodology is effective, albeit in low yields.