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 constants with chiral aminoethanol derivatives, including 2-amino-2-phenylethanols having an electron-donating or an electron-withdrawing group, were determined in chloroform by means of UV-vis titration methods. The enantioselectivities 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 and guests on the binding abilities and enantioselectivities is discussed. The structures of the complexes were investigated on the basis of the (1)H NMR and UV-vis spectra.