Enantioselective Synthesis of Polycyclic Aromatic Hydrocarbon (PAH)‐Based Planar Chiral Bent Cyclophanes by Rhodium‐Catalyzed [2+2+2] Cycloaddition
Yukimasa Aida, Juntaro Nogami, Haruki Sugiyama, Hidehiro Uekusa, Ken Tanaka
Abstract
Abstract The enantioselective synthesis of polycyclic aromatic hydrocarbon (PAH)‐based planar chiral cyclophanes was achieved for the first time by the rhodium‐catalyzed intramolecular regio‐ and enantioselective [2+2+2] cycloaddition of tethered diyne‐benzofulvenes followed by stepwise oxidative transformations. The thus synthesized planar chiral bent cyclophanes, that possess bent p ‐terphenyl‐ and 9‐fluorenone‐cores, were converted to 9‐fluorenol‐based ones with excellent ee values of >99 % by diastereoselective 1,2‐reduction. These 9‐fluorenol‐based cyclophanes exhibited high fluorescence quantum yields, which were significantly higher than that of an acyclic reference molecule (78–82 % vs. 48 %). The bending effect on the chiroptical property was also examined, which revealed that the anisotropy factors ( g abs values) for electronic circular dichroism (ECD) of these 9‐fluorenol‐based planar chiral bent cyclophanes increase as the tether length becomes shorter.