Synthesis of new proton-ionizable crown ether compounds containing substituted lh-pyridin-4-one subcyclic units

Five novel pyridono‐18‐crown‐6 (10‐14) and two new benzyloxy‐substituted pyridino‐18‐crown‐6 (15 and 16) ligands have been prepared. By the catalytic hydrogenative removal of the benzyl group from the benzyloxy moiety at position 4 of the pyridine ring of 15 and 16, pyridono‐18‐crown‐6 ethers 5 and 12 were obtained. These ligands were transformed to their 3,5‐dibromo (10 and 13) and 3,5‐dinitro derivatives (11 and 14) by treatment with bromine in methylene chloride and nitric acid in acetic anhydride, respectively. The latter proton‐ionizable crown ethers have pKavalues of about 7.5 for 10 and 13 and 4.5 for 11 and 14. Thus, they are good candidates for complexation and proton‐coupled transport of selected cations.