The formation of complexes between aza derivatives of crown ethers and primary alkylammonium salts. Part 7. Chiral derivatives of aza crown ethers

Abstract

A number of optically active derivatives of diaza-15-crown-5 and diaza-18-crown-6 have been synthesised using amino acids as the source of chirality. The diaza-18-crown-6 derivatives (21) show enantioselectivity in the complexation of 1-phenylethylammonium thiocyanate in methylene chloride as determined by ¹H n.m.r. spectroscopy. The degree of enantioselectivity depends upon the substituents on the nitrogen atoms of the macrocycle and although the N,N-dibenzyl derivatives (21) show moderately high enantioselectivity, the N,N-dimethyl derivatives (20) do not. In the presence of water the hosts (21) apparently form hydrated complexes with guest alkylammonium cations with very little enantioselectivity.