Copper-Catalyzed Perarylation of Cyclopentadiene: Synthesis of Hexaarylcyclopentadienes

While hexaphenylsilacyclopentadiene (hexaphenylsilole) is viewed as an archetypal Aggregation-Induced Emission (AIE) luminogen, its isostructural hydrocarbon surrogate hexaphenylcyclopentadiene has strikingly never been investigated in this context, most probably due to a lack of synthetic availability. Herein, we report a straightforward synthesis of hexaphenylcyclopentadiene, via the direct perarylation of cyclopentadiene upon copper(I) catalysis under microwave activation, with the formation of six new C-C bonds in a single synthetic operation. Using zirconocene dichloride as a convenient source of cyclopentadiene and a variety of aryl iodides as coupling partners, this copper-catalyzed cross-coupling reaction gave rise to a series of unprecedented hexaarylcyclopentadienes, displaying promising properties as AIE luminogens. In addition, these propeller-shaped perarylcyclopentadienes are direct precursors of π-extended conjugated polycyclic compounds, and their cyclodehydrogenation under Scholl reaction conditions yielded helicenic 17,17-diarylcyclopenta[l,l’]diphenanthrenes. These structurally complex polyannelated fluorene derivatives can now be prepared in only two synthetic steps from cyclopentadiene for applications as organic semiconductors or fluorophores.