Planar Chirality

Fig. １

　Pillar[n]arenes have planar chirality depending on the position of the alkoxy group on the rims. Usually, racemization proceeds by the rotation of the benzene unit. However, by introducing bulky cyclohexyl groups on the rims of pillar[5]arene, the rotation of the benzene ring is suppressed due to its bulkiness, and the pS / pR enantiomer can be isolated by chiral column chromatography. The rotation of the unit was also suppressed by introducing a π-conjugated unit from di-reactive pillar[5]arene containing one hydroquinone unit, and the enantiomer could be isolated. We also synthesized bi-cyclic structure. Because of formation of self-inclusion complex (in-state), the rotation of the unit was suppressed and the enantiomers could be separated. By addition of competitive achiral guest, the ring located inside of the cavity was kicked out to outside of the cavity, which was triggered planar chiral inversion.


Fig. 2