ability in methanol towards the alkali cations K+, Rb+ and Cs+. The binding substantially increases in basic solution because of the reversible addition of methoxideion to the heteroaromatic ring to form a neutral 4H adduct. The effect of the length of the polyoxyethylene chain and of the presence of a bulky group (tert-butyl) in the γ position of the heteroaromatic ring has been quantitatively investigated
The pyrylium corands 1a, 1b and the thiopyrylium corands 2a, 2b, were prepared in good yields by heterocyclization of the macrocyclic 1,5-pentanediones 4a, 4b, whereas the pyridine corands 3a, 3b were obtained by reacting 1a and 1b, respectively, with ammonium acetate. NMR data and molecular mechanics calculations suggest that the heteroaromatic nuclei tend to fill the cavity of the macrorings.