Synthesis of Planar meso-Aryl Rosarins: A Reversible Antiaromatic/Aromatic Interconversion

Novel 24π antiaromatic and 26π aromatic meso-aryl rosarins were successfully obtained for the first time from β-free bipyrrole through a one-pot synthesis. Because of the absence of substituents at the β-positions of the pyrrole units, the β-free pristine rosarin backbones were highly planar, as confirmed using X-ray crystallography. Optical measurements indicated interconversion between 24π antiaromatic and 26π aromatic β-free pristine rosarin via redox reactions, which was not observed in distorted β-dodecamethyl rosarin.