Locking the Dynamic Axial Chirality of Biphenyl Crown Ethers through Threading.

This paper describes the syntheses of [2]rotaxanes comprising 23‐ and 26‐membered biphenyl crown ethers as the macrocyclic components and secondary ammonium ions as the dumbbell‐shaped components, and the locking of the dynamic axial chirality of the biphenyl moieties in these structures. Chiral high‐performance liquid chromatography (HPLC) revealed that our [2]rotaxane featuring the 26‐membered crown ether racemized at room temperature, but the racemization of the [2]rotaxane featuring the 23‐membered crown ether did not proceed at room temperature over a period of three days. After separation of the enantiomers of the [2]rotaxane incorporating the 23‐membered crown ether through chiral HPLC, we studied its racemization at elevated temperature. The rate of stereoinversion in dimethylsulfoxide (a polar solvent) was faster than that in o‐dichlorobenzene (a nonpolar solvent), and herein we discuss these kinetic parameters. [ABSTRACT FROM AUTHOR]