Asymmetrical cis-5,6-dimethyl-6-oxyacetoxy-(2,3)(9,10)-dibenzo-16-crown-5 w
as synthesized by a multi-step sequence and its stereochemistry determined
by NOE experiments. Introduction of the 6-methyl group markedly reduces the
stability constant for complexation of Na+ and K+ by the ionized form of t
he lariat ether carboxylic acid.