High-yield diastereoselective synthesis of planar chiral [2]- and [3]rotaxanes constructed from per-ethylated pillar[5]arene and pyridinium derivatives

Planar chiral 2]- and 3]rotaxanes constructed from pillar5]arenes as wheels and pyridinium derivatives as axles were obtained in high yield using click reactions. The process of rotaxane formation was diastereoselective; the obtained 2]rotaxane was a racemic mixture consisting of (pS, pS, pS, pS, pS) and (pR, pR, pR, pR, pR) forms of the per-ethylated pillar5]arene (C2) wheel, and other possible types of the 2]rotaxane did not form. Isolation of the enantiopure 2]rotaxanes with one axle through (pS, pS, pS, pS, pS)-C2 or (pR, pR, pR, pR, pR)-C2 wheels was accomplished. Furthermore, pillar5]arene-based 3]rotaxane was successfully synthesized by attachment of two pseudo 2]rotaxanes onto a bifunctional linker. 3]Rotaxane formed in a 1:2:1 mixture with one axle threaded through two (pS, pS, pS, pS, pS)-C2, one (pS, pS, pS, pS, pS)-C2 and one (pR, pR, pR, pR, pR)-C2 (meso form), or two (pR, pR, pR, pR, pR)-C2 wheels. The 3]rotaxane enantiomers and the meso form were successfully isolated using appropriate chiral HPLC column chromatography. The procedure developed in this study is the starting point for the creation of pillar5]arene-based interlocked molecules.