π-Radical Cascade to a Chiral Saddle-Shaped Peropyrene

Abstract

Reactions of open-shell molecular graphene fragments are typically thought of as undesired decomposition processes because they lead to the loss of desired features like π-magnetism. Oxidative dimerization of phenalenyl to peropyrene shows, however, that these transformations hold promise as a synthetic tool for making complex structures via formation of multiple bonds and rings in a single step. Here, we explore the feasibility of using this “undesired” reaction of phenalenyl to build up strain and provide access to non-planar polycyclic aromatic hydrocarbons. To this end, we designed and synthesized a biradical system with two phenalenyl units linked via a biphenylene backbone. The design facilitates an intramolecular cascade reaction to a helically twisted saddle-shaped product, where the key transformations—ring-closure and ring-fusion—occur within one reaction. The negative curvature of the final peropyrene product, induced by the formed eightmembered ring, was confirmed by single-crystal X-ray diffraction analysis and the helical twist was validated via resolution of the product’s enantiomers that display circularly polarized luminescence and high configurational stability.