화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.141, No.29, 11583-11593, 2019
Orchestrating Communications in a Three-Type Chirality Totem: Remote Control of the Chiroptical Response of a Mobius Aromatic System
Among the various types of chirality (central, axial, helical, planar, etc.), that inherent to Mobius topology remains almost unexplored, partly due to the difficulty to access Mobius compounds. Over the past decade, [28]hexaphyrins have been revealed to be among the best candidates to build on Mobius aromaticity. Whereas their flexibility needs to be controlled to get P/M twist enantioselectivity, it could be of great interest to sustain dynamic chirality transfer. In this context, we report herein the first example of a Mobius aromatic ring capped by a cavity, consisting of a Mobius [28]hexaphyrin doubly linked to an alpha-cyclodextrin. This unique design affords a "totem" of three different chirality elements arising from the cyclodextrin (fix central chirality), the bridging pattern (dynamic planar chirality), and the hexaphyrin (dynamic topological chirality). Chirality transfers (as shown in the TOC graphic) are characterized by a stereospecific planar-to-topological communication (diastereomeric excess >95%; the highest asymmetric selectivity reported to date for a Mobius ring) combined to a stereoselective central-to-planar communication (up to 60% diastereomeric excess). Interestingly, the stereoselectivity is remotely controlled by coordination of an achiral effector to the hexaphyrin, increasing up to 5 times the chiroptical response of the Mobius aromatic pi-system. These results highlight the advantageous use of dynamic chirality transfers to further incorporate Mobius chirality and aromaticity into all kinds of stimuli-responsive devices.