讲座摘要：

      Inherently chiral macrocycles, e.g., pillar[5]arenes and tiara[5]arenes, are abundant, but their asymmetric nature is often overlooked, as many such derivatives exist as stereolabile racemic mixtures in solution. Their micro-to-milli-second enantiomerization half-lives associated with the rapid inversion of flexible macrocyclic scaffold make chromatographic separation practically unfeasible. In the solid state, on the other hand, a small portion of these chiral macrocycles conglomerates instead of racemates upon crystallization, indicating that fluxional conformers are not only confined in crystalline environment but also spontaneously resolved as homochiral crystals. Extensive X-ray crystallographic and circular dichroism spectroscopic characterizations, in combination with careful examination of crystal morphology, revealed the connections among absolute configuration, chiroptical properties, and hemihedrism of single crystals of such fluxional macrocycles. This study revisits the triage approach–first employed by Louis Pasteur in 1848 on tartrates–for the resolution of conformational isomers with a moderate inversion barrier of 47.8 kJ/mol, which is generally considered “irresolvable”.