Synthesis and ¹H NMR studies of vinyl-substituted calix[4]arene derivatives: Enhanced cation-π interactions with extended calix[4]arene π-systems

A new class of calix[4]arene derivatives bearing vinyl groups on the upper rim has been synthesized using the condensation of starting 5,17-diformyl-2526,27,28-tetrapropoxycalix[4]arene with malonic acid in the presence of piperidine as a catalyst. The corresponding vinyl substituted derivative can be isolated directly in 40% yield and serves as a starting point for the preparation of calix[4]arene derivatives fixed either in the cone or 1,3-alternate conformations. The complexation ability of such compounds towards Ag⁺ cation has been studied with the help of ¹H NMR spectroscopy and MS spectroscopy. It was shown that the presence of the double bonds at upper rim can enhance binding constants as compared with unsubstituted derivatives due to their additional cation-π interactions. The significance of the double bonds for quaternary pyridinium salts has been also demonstrated by the enhanced binding ability.