Diastereoselective Polypseudorotaxane Formation with Planar Chiral Pillar[5]arenes via Co‐crystallization Processes

Abstract

As the number of chiral ring molecules in chiral polyrotaxane increases, the number of possible stereoisomers exponentially increases. Consequently, the selective synthesis of a specific stereoisomer becomes much more challenging. To address this problem, we co‐crystallized poly(ethylene glycol) and a diastereomeric ring molecule, pillar[5]arene, in the solid state. The co‐crystallization formed polypseudorotaxanes with a high diastereomeric excess (ca. 88% de), meaning that polypseudorotaxanes containing (S, pS) stereoisomer pillar[5]arene rings were synthesized selectively. By contrast, in a solution and evaporation systems, the selectivity remained low (ca. 10% de). The results suggested that the packing effect by the co‐crystallization contributed to the denser assembly of ring molecules on the polymeric chain, resulting in the diastereoselective formation. High diastereoselectivity was also observed even in higher‐molecular‐weight poly(ethylene glycol)s. These selectivities arose from the cooperative effects of the ring molecules on the polymeric chain, which were supported by calculating the stabilization energy.