Inherently Chiral Cages via Hierarchical Desymmetrization

A new type of cage inherent chirality was accessed by hierarchical desymmetrization of a D_3h-symmetric prismlike cage motif. The dissymmetric C_3v cage precursor C1 bearing two different phloroglucinol caps was first synthesized. The subsequent progressive substitutions on the three triazine arms by different nucleophiles furnished the desired C₁-symmetric inherently chiral cages C3 and C4 with rich structural diversity. Resolution of the racemic cages was achieved by chiral chromatography, and the enantiopure cages were readily obtained on the gram scale. Convenient post-synthetic transformations of the chiral cages with retention of enantiomeric purity were also realized. The absolute configuration was determined by X-ray crystallography, and a chirality descriptor was provided to define the cage chirality. With the inherently chiral array of the electron-deficient triazine surfaces constituting three individual chiral V-shaped π cavities, regio- and enantioselective anion-π binding was probed for the first time with minimum interference of other interactions. As exemplified with chiral phosphate anions (CPAs), it was found that cage (-)-C3a preferably binds (S)-CPA^- in the most electron-deficient cavity through synergistic anion-π interactions with considerable chiral selectivity.