Calixarenes. 28. Synthesis, Structures, and Conformations of Aroylates of Calixarenes

Article abstract of DOI:10.1021/jo00037a036

A study of the aroylation of calix<6>arenes under a variety of conditions has shown that the reaction often yields the 1,2,4,5-tetraester as a major product but that the outcome is dependent both on the aroylating agent and the calixarene.The best results have been obtained with p-nitrobenzoyl chloride which reacts with p-tert-butylcalix<6>arene (1a) to yield a separable mixture containing ca. 40percent tetraester 2a and 30percent pentaester 3 when NaH is used as the base or up to 85percent of the tetraester when 1-methylimidazole is used as the base.In comparable fashion benzoyl chloride and p-nitrobenzoyl chloride react with 1a and 1b, respectively, to yield the tetraesters 2b and 2c, whereas p-allylcalix<6>arene (1c) reacts under the same conditions to produce the hexaester 6.With limiting amounts of p-nitrobenzoylating agent the diesters 4 and 5 have been isolated in low yields. 3,5-Dinitrobenzoyl chloride gives less satisfactory results, producing mixtures containing six or more esters from which only small amounts of the 1,2,4,5-tetraester 2d have been isolated.The structure and conformation of the products have been established by elemental analysis, mass spectral measurements, and 1H NMR techniques.In the case of 2a this includes difference NOE and transient NOE determinations which show that the compound exists in a conformation in which two of the aroylated moieties are canted inward so that their p-tert-butyl groups occupy the two faces of the calix<6>arene cavity, thus self-complexing the compound and preventing intermolecular complexation.