Bridging Chiral Calix[4]arenes: Description, Optical Resolution, and Absolute Configuration Determination

A new chiral calix[4]arene constructed from asymmetric substitution on bridging methylenes, phenyl rings, and (or) oxygen atoms was tentatively named as “bridging chiral” calix[4]arene that have point chirality on its substituted bridging methylene. A new approach to enantiopure bridging chiral calix[4]arenes through optical resolution is presented for the first time. As a result, a pair of enantiopure bridging chiral calix[4]arene carboxylic acids monobridge‐substituted with an equatorial N,N′‐dimethylformamidyl group (4a and 4b) were easily prepared by the optical resolution of their racemate with chiral auxiliary (S)‐Binol. The absolute configurations of the enantiomers were determined by X‐ray crystallographic analysis. Bridging chiral calix[4]arenes (–)‐4a and (+)‐4b are a pair of new chiral calix[4]arene enantiomers that have point chirality on their substituted bridging methylene. Their optical resolution is easily achieved with chiral auxiliary (S)‐Binol. The absolute configurations of the enantiomers were determined by X‐ray crystallographic analysis.