Dynamic Figure Eight Chirality: Multifarious Inversions of a Helical Preference Induced by Complexation

We demonstrate two types of inversion
of a helical preference upon
the 1:1 complexation of a dynamic figure eight molecule with a guest
molecule through the controlled transmission of point chirality. We
designed a series of macrocycles that prefer a nonplanar conformation
with figure eight chirality. These macrocycles are composed of a chirality-transferring
unit (terephthalamide) and a structure-modifying unit (two o-phenylene rings spaced with a varying number of triple
bonds). The former unit provides a binding site for capturing a guest
molecule through the formation of hydrogen bonds. The attachment of
chiral auxiliaries to the former unit induces a helical preference
for a particular sense through the intramolecular transmission of
point chirality. For relatively small-sized macrocycles, the preferred
sense was reversed upon complexation with an achiral guest. Contrary
preferences before and after complexation were both seen for chiral
auxiliaries associated with a figure eight host through two-way intramolecular
transmission of the single chiral source. Alternatively, the helical
preference induced in relatively large-sized macrocycles was reversed
only when a figure eight host formed a 1:1 complex with a particular
enantiomeric guest through the supramolecular transmission of point
chirality in the guest. This stereospecific inversion of a helical
preference is rare.