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 pKa values 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.
ASJC Scopus subject areas
- Organic Chemistry