Absolute Configuration Determination from Low ee Compounds by the Crystalline Sponge Method. Unusual Conglomerate Formation in a Pre-Determined Crystalline Lattice

When chiral compounds with low enantiomeric excess (ee, R:S=m:n) were absorbed into the void of the crystalline sponge (CS), enantiomerically pure [(R)(m)(S)(n)] chiral composites were formed, changing the centrosymmetric space group into non-centrosymmetric one. The absolute configuration of the analyte compounds was elucidated with a reasonable Flack (Parsons) parameter value. This phenomenon is characteristic to the post-crystallization in the pre-determined CS crystalline lattice, seldom found in common crystallization where the crystalline lattice is defined by an analyte itself. The results highlight the potential of the CS method for absolute configuration determination of low ee samples, an often encountered situation in asymmetric synthesis studies.

Automated summary

Absorbing chiral compounds with low enantiomeric excess into the crystalline sponge void can lead to the formation of enantiomerically pure chiral composites, changing the space group from centrosymmetric to non-centrosymmetric. This phenomenon is characteristic of post-crystallization in the predetermined CS lattice, highlighting the potential of the CS method for determining absolute configuration in low ee samples.