2020 Volume 78 Issue 8 Pages 770-781
Helicenes are nonplanar 3D screw-shaped polycyclic compounds based on ortho-fused benzenes or aromatic rings, unlike other chiral compounds, and exhibit unique structural, optical, and electronic features. Thus, a large number of helicenes were investigated so far for a broad range of applications in study on chirality, catalysis, optoelectronics, and biology. In this study, a variety of carbo［5］helicenes with a substituent exclusively oriented toward the interior curvature of the helix are synthesiszed by PtCl2-catalyzed cycloisomerization. These［5］helicenes show a high enough configurationally stability. Based on this research, a series of novel optically active［5］helicene-derived phosphine ligands (L1, with a 7,8-dihydro［5］helicene core structure- and L2, with a fully aromatic［5］helicene core structure) were synthesized and applied to Pd-catalyzed asymmetric reactions. Furthermore, we recently designed and synthesized internal-edge-substituted coumarin-fused［6］helicenes with a phenyl substituent. Of particular note, the enantiomerically pure crystal adopted a one-dimensional columnar structure, which clearly showed the importance of the proper choice of a substituent for columnar arrangement.
