Indeno[2,1-c]fluorene Quasi[8]circulenes Through Intramolecular Cyclization.

The study of polycyclic aromatic hydrocarbons has become a cornerstone of chemical sciences, providing crucial guidance for advancing a wide range of fields. Within this context, quasi[8]circulenes and indenofluorenes (IFs) have gained considerable attention due to their rich chiroptical, optoelectronic, supramolecular, and redox properties. However, their combined integration into a single molecular framework has not yet been realized. This work demonstrates that curved indeno[2,1-c]fluorene quasi[8]circulenes are easily accessible through an intramolecular cyclization of a readily available helicene diketone. The cyclization is high yielding and accompanied by an unexpected regioselective triflation that-alongside both ketones-allows orthogonal functionalization. This synthetic utility offers great potential for incorporating 8-membered rings and formally antiaromatic as-indacene moieties into complex architectures. Herein, a series of fully conjugated antiaromatic indeno[2,1-c]fluorene quasi[8]circulenes were synthesized and studied spectroscopically and electrochemically, showcasing the rich properties of these rare, purely carbon-based quasi[8]circulenes. It is shown that the studied compounds display multiple accessible redox states at mild potentials, which can be significantly altered through adequate substituents. These substituents additionally induce unprecedented aggregation behavior for one of the compounds. Furthermore, the studied IFs exhibit chirality arising from the curved structure of the quasi[8]circulenes, which allowed studying chiroptical properties for one of the structures.