Inherently Chiral Calix[5]arenes Incorporating an Axially Chiral Binaphthyl Moiety: Synthesis, Structures and Chiral Recognition

Inherent chirality was generated by regioselective monoalkylation of 1,3‐substituted calix[5]crown‐6 incorporating an axially chiral BINOL moiety, with ethyl bromoacetate. The resultant diastereomers 4a and 4b , which possess both axial chirality and inherent chirality, were readily separated by column chromatography. Respective hydrolysis afforded diastereomeric acids 5a and 5b . 1 H NMR spectra and X‐ray crystallography established that esters 4a and 4b feature a cone‐in conformation, which disappears in the corresponding acids 5a and 5b due to intramolecular hydrogen‐bonding between the carboxyl group and a glycolic oxygen atom. Amino alcohol‐induced fluorescence quenching was observed for 5a and 5b . The highest enantioselectivity, based on the ratio of Stern–Volmer constants K SV( S ) / K SV( R ) , reached 1.90 in the case of 5a with 2‐amino‐1‐phenylethanol ( G1 ), and 5b with phenylalaninol ( G2 ). The highest diastereoselectivity of 1.83, measured by K SV( 5a ) / K SV( 5b ) , occurs in the case of 5a / 5b with ( R )‐ G2 .