Enantioselective complexation of phenolic crown ethers with chiral aminoethanol derivatives: effects of substituents of aromatic rings of hosts and guests on complexation

Optically active azophenolic crown ethers having phenyl groups substituted at the respective para-position were prepared and their association constan ts with chiral aminoethanol derivatives, including 2-amino-2-phenylethanols having an electron-donating or an electron-withdrawing group, were determi ned in chloroform by means of UV-vis titration methods. The enantioselectiv ities of these crown ethers are estimated from the ratio of the association constants K-R/K-S and the effect of aromatic substituents of both hosts an d guests on the binding abilities and enantioselectivities is discussed. Th e structures of the complexes were investigated on the basis of the H-1 NMR and UV-vis spectra.