Helicenes Fused with Hexafluorocyclopentene (HFCP): Synthesis, Structure, and Properties

Helicenes fused with hexafluorocyclopentene (HFCP) were synthesized by oxidative photocyclization of stilbene derivatives (the Mallory reaction). Of the newly-obtained fluorinated helicenes, the [7]helicenes bearing one- or three-HFCP units were structurally characterized by X-ray crystallographic analysis. The attempted synthesis of [9]helicene fused with three HFCP units resulted in the unexpected formation of a novel double helicene consisting of [4]- and [6]-helicenes sharing peripheral benzene rings. Optical properties and chiral resolutions of the newly obtained HFCP-substituted helicenes are also described.