10.1002/chem.202001450
The study presents the enantioselective synthesis of polycyclic aromatic hydrocarbon (PAH)-based planar chiral bent cyclophanes using rhodium-catalyzed [2+2+2] cycloaddition. The researchers achieved this by intramolecular regio- and enantioselective cycloaddition of tethered diyne benzofulvenes, followed by stepwise oxidative transformations. The synthesized planar chiral bent cyclophanes, featuring bent p-terphenyl and 9-fluorenone cores, were converted into 9-fluorenol-based cyclophanes with excellent enantiomeric excess (ee) values of over 99%. These cyclophanes exhibited high fluorescence quantum yields, significantly higher than an acyclic reference molecule, due to reduced flexibility and suppressed radiationless deactivation. The study also found that the anisotropy factors for electronic circular dichroism (ECD) increased as the tether length became shorter, enhancing the bending effect and reducing twist. The work demonstrates the utility of rhodium-catalyzed [2+2+2] cycloaddition for constructing PAH-based planar chiral bent cyclophane structures with high enantioselectivity and unique optoelectronic properties.