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Synthesis and Conformational Evaluation of p-tert-Butylthiacalix[4]arene-crowns

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posted on 28.05.2004, 00:00 by Fijs W. B. van Leeuwen, Hans Beijleveld, Huub Kooijman, Anthony L. Spek, Willem Verboom, David N. Reinhoudt
Bridging of p-tert-butylthiacalix[4]arene afforded 1,3-dihydroxythiacalix[4]arene-monocrown-5 (3b), 1,2-alternate thiacalix[4]arene-biscrown-4 and -5 (4a,b), and 1,3-alternate thiacalix[4]arene-biscrown-5 and -6 (5a,b), depending on the metal carbonates and oligoethylene glycol ditosylates used. Starting from 1,3-dialkylated thiacalix[4]arenes, the corresponding bridging reaction gave 1,3-alternate, partial-cone, and cone conformers 1019, depending on the substituents present. Temperature-dependent studies revealed that the conformationally flexible 1,3-dimethoxythiacalix[4]arene-crowns 10ac exclusively occupy the 1,3-alternate conformation. Demethylation exclusively gave the cone 1,3-dihydroxythiacalix[4]arene-crowns (3a,c), which could not be obtained by direct bridging of thiacalix[4]arene. The different structures were assigned on the basis of several X-ray crystal structures and extensive 2-D 1H NMR studies.