Novel C1-symmetric chiral crown ethers bearing rosin acids groups: synthesis and enantiomeric recognition for ammonium salts

Four types of novel C1-symmetric chiral crown ethers including 28-crown-8, 20-crown-6, 17-crown-5 and 14-crown-3 (9a-m) were synthesized and their enantiodiscriminating abilities with protonated primary amines (10-14) were examined by 1H NMR spectroscopy. 20-crown-6 crown ethers exhibited good chiral recognition properties toward these guests and showed different complementarity to some chiral guests, indicating that 20-crown-6 crown ethers could be used as a chiral NMR solvating agent to determine the enantiopurity of these guests. In addition, the binding model and binding site between the hosts and guests were also studied by the computational modeling and experimental calculation.