Efficient syntheses of calix[4]arenes in the 1,2-alternate conformation via intramolecular benzoate ester migrations

Abstract

A previously known imidazole-initiated intramolecular ester migration was modified by replacing the imidazole with Cs 2CO 3 to effect the efficient conversion of 25, 27-bis- p-methoxy-, 25,27-bis- p-fluoro and 25, 27-bisbenzoyloxycalix[4]arene in the flattened cone conformation to the corresponding 25,26-benzoyloxy compounds in the 1,2-alt. The rearrangement was highly efficient for the unsubstituted and methoxy-substituted esters; the 1,2-alternate isomers were isolated in 80–88% yield, but less efficient for the fluoro-substituted ester (isolated yield 58%). The p-methoxy- and p-fluoroesters were further functionalized in subsequent alkylation reactions with methyl p-toluenesulfonate and pentaethyleneglycol-di- p-tosylate to produce dimethoxy- and calixcrown-ester derivatives in the 1,2-alt. in moderate to good yields. The high yields of the 1,2-alt. are attributed to a π-metal template effect involving the soft cesium ion from the base, two aryl rings and the two phenolate oxygens of the deprotonated calixarene.