5,11,17,23-Tetra-tert-butyl-2,8,14,20-tetrathiacalixarene-25,26,27,28- tetrol (TCA) underwent facile tetra-O-alkylation by treatment with ethyl bromoacetate in the presence of an alkali carbonate as base catalyst in DMF or acetone to provide a mixture of conformational isomers (cone, partial cone, and 1,3-alternate) of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-2,8, 14,20-tetrathiacalixarene(1), the stereochemistries of which were unambiguously assigned by 1H NMR and X-ray analysis. The isomer distribution depended significantly on the base used, thus providing a facile route for the preparation of a particular conformer; Na2CO3, K2CO3, and Cs2CO3 gave cone- (77% yield), partial-cone- (58% yield), and 1,3-alternate-1 (78% yield) in acetone, respectively. Cone- and partial-cone-1, in turn, showed preference for Na+ and K+, respectively, in an ion-pair extraction study, while 1,3-alternate-1 preferred most Rb+ ion, followed by K+ and then Cs+. These results imply that the size of the cavities provided by the (ethoxycarbonyl)methoxy groups arranged on the periphery of the thiacalixarene skeleton is in the order cone- < partial-cone- < 1,3-alternate-1. The ion selectivity of cone-1 was rather better than that of the methylene-bridged counterpart. 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy] calixarene (2). The stoichiometry of the complex of cone-1 with Na+ ion was determined to be 1:1 with the stability constant of 102.85 mol-1 dm3 in 50 (v/v)% CDCl3-CD3OD.
|Number of pages||6|
|Journal||Journal of the Chemical Society. Perkin Transactions 2|
|Publication status||Published - 1998 Dec|
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