Abstract Two new 18-membered tetralactams with two dimethyleneoxy moieties are synthesized by direct macrocyclization or steps reaction. In the latter case symmetrical or unsymmetrical compounds can be obtained. The unsymmetrical tetralactam shows a very high selectivity for barium vs. Na+ and Zn 2+ and to a lesser extent vs. K+, Mg 2+ and Ca 2+ in the extraction procedure with picrates. In addition, the stability constants are determined ...
