CALIXARENES .26. SELECTIVE ESTERIFICATION AND SELECTIVE ESTER CLEAVAGE OF CALIX[4]ARENES

Methods have been developed for converting p-tert-butylcalix[4]arene (1a) in high yield to the 25-monoester 7, the 25,26-diesters 5 and 6, the 25,27-diester 4a, and the 25,26,27-triesters 2 and 3 in which the aryl groups are 3,5-dinitrophenyl moieties. Concomitantly, methods have emerged whereby these esters can be selectively cleaved or rearranged. By appropriate choice of reaction conditions the 25,27-diester 4a can be selectively cleaved with imidazole bases to the monoester 7 or rearranged to the 25,26-diester 5; the triesters 2 and 3 can be converted to their conformationally related 25,26-diesters 5 (a chiral compound) and 6. The effects of variations in solvent, organic base, and reaction time on the conversion of 4a to 7, along with semiquantitative kinetic data, suggest that two or more molecules of the imidazole are involved in the activated complex of the rate-determining step in the aminolysis. These syntheses provide easy access to the mono-, di-, and triesters, thus expanding the techniques for obtaining selectivity para-substituted calixarenes via selective de-tert-butylation. Thus, removal of three, two, or one tert-butyl group, respectively, from the monoester 7, the diesters 4a and 5, and the triester 2 yields the corresponding mono-, di-, and tri-tert-butylated analogues 12a-d. Acylation of 12b, for example, can be effected at the vacated para positions to produce the diacylcalix[4]arenes 15a and 15b. Collectively, the system provides an example of how careful control of reaction conditions can be used to advantage in determining product formation.