Catalytic ability of a flexible octopus-type calix[6]arene in ester-forming reactions and its structural properties

Abstract

The ester-forming reaction of alkali metal carboxylates with alkyl halides was catalyzed by the octopus-type calix[6]arene 1 which bears six 3,6,9-trioxadecyl substituents at the phenolic oxygens. The catalytic ability of 1 was significantly large in CH 2 Cl 2 and CH 3 CN but negligible in less polar solvents such as benzene and dioxane. The catalytic ability is also affected by the amount of water present in the reaction system. A similar solvent effect was found in the alkali metal cation extraction by 1 from aqueous solutions to organic solvents. The conformation and structural mobility of 1 in organic solvents were studied by 1 H NMR spectroscopy at varying temperatures. Compound 1 had a 1,4-anti conformation both in CD 2 Cl 2 and C 6 D 6 , but the orientation of the substituents on the aromatic rings of 1 varied with temperature. The reactivity features of 1 are discussed on the basis of its structural properties