BRIDGED CALIX[6]ARENES IN THE CONE CONFORMATION - NEW RECEPTORS FOR QUATERNARY AMMONIUM CATIONS

The synthesis of calix[6]arene crown ethers 3 and 4 has been accomplished for the first time by selective bridging of the parent macrocycles. The alkylation of 3 with alpha-chloro-N,N-diethyl acetamide produces a compound 6 whose conformational flexibility is strongly reduced and which assumes a cone conformation both in solution and in the solid state. Compound 6 represents a new type of ditopic receptor which binds tetramethylammonium cation in the polar region at the lower rim, showing an association constant K-a=750 M(-1) in CDCl3.