Novel chiral Oxa-bridged Calix[2]arene[2]triazine derivatives as NMR chiral reagents for enantioselective recognition of α-racemic carboxylic acids

Abstract

A new family of chiral tetraoxacalix[2]arene[2]triazine receptors (2a–2c) have been synthesized efficiently in 69–73% yields. By 1H NMR spectroscopy, the chiral enantiodiscrimination ability of novel hosts against a series racemic carboxylic acids were examined. The chiral calix[2]arene[2]triazine-based compounds were found to have good enantiomeric recognition ability to racemic carboxylic acids. We also observed that the tetraoxacalix[2]arene[2]triazine derivative 2c is a more versatile chiral solvating agents than 2a and 2b, as 2c shows a better performance for the determination of the enantiomeric excess. The molar ratio of the each enantiomers of guest molecules with receptors were examined by using Job plots, respectively. The graphics show that the hosts form 1:1 complexes with all of the guests.