Short Synthesis of [5]- and [7]Phenacenes with Silyl Groups at the Axis Positions

[5]Phenacene with trimethylsilyl groups at the axis positions was synthesized by the ruthenium-catalyzed direct C-H arylation of a 1-formyl-7-phenanthrene-derived aldimine, followed by sequential Wittig olefination and bismuth-catalyzed cyclization of the resulting vinyl ethers. By using the same synthetic building blocks and sequential Wittig olefination and photocyclization, the number of fused benzene rings was readily increased to seven to afford 3,12-disilyl[7]phenacene. The introduction of silyl groups endowed the [n]phenacene frameworks with good solubility, as well as enabling further functionalization. The electronic structure of these new [n]phenacenes was determined by photophysical measurements and by density functional theory calculations, which clearly implied effective conjugation throughout the entire π framework.