Synthesis and complexation properties of pyrimidine-derived crown ether ligands [1]

Five new proton-ionizable macrocyclic ligands containing a pyrimidone-subcyclic unit, 6-10, were prepared from the previously prepared pyrimidinocrown ethers 1-5 (see Figure 1 and Scheme 1). One of the new proton-ionizable crown ethers is chiral. The proton-ionizable pyrimidonocrown ethers were prepared in high yields by treating the appropriate methoxy-substituted pyrimidinocrown with 5 M sodium hydroxide in a 50% alcohol-water mixture. Complexation properties of four of the pyrimidine-derived macrocycles were studied by various nmr techniques. Pyrimidono-18-crown-6 (9) forms a strong complex with benzylammonium perchlorate and also forms a complex with benzylamine. (S,S)-Dimethyl-substituted pyrimidino- and pyrimidono-18-crown-6 ligands 4 and 9 form stronger complexes with the (R)-form of alpha-(1-naphthyl)ethylammonium perchlorate than with the (S)-form. (S,S)-Dimethyl-substituted pyrimidono-18-crown-6 (9) also forms a stronger complex with (R)-alpha-(1-naphthyl)ethylamine than with the (S)-form. The crystal structure for compound 7 is reported.