Macrocyclic, linear and starlike assemblies of calix[4]arenes covalently bridged by methylenes at the upper rims: simple route to novel receptors with defined polycavities

Chloromethylation of 5,17-di-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene with chloromethyl methyl ether in the presence of zinc chloride led to the formation of macrocyclic and linear oligomers containing three to five calix[4]arenes bridged via methylenes at the upper rims. Under the identical conditions, however, 5,17-di-tert-amyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene was converted into a mixture of linear dimer and trimer in yields of 39.5 and 34%, respectively. Only dimer was obtained as the sole product in 41% yield when 25,27-dihydroxy-26,28-diethoxycalix[4]arene was used. Efficient synthesis of linear or starlike polycalixarenes was achieved utilizing the Friedel–Crafts reaction of debutylated or partially debutylated calix[4]arenes with chloromethylated calix[4]arene promoted by anhydrous zinc chloride.