Synthesis and Conformational Evaluation of p-tert-Butylthiacalixarene-crowns
datasetposted 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-butylthiacalixarene afforded 1,3-dihydroxythiacalixarene-monocrown-5 (3b), 1,2-alternate thiacalixarene-biscrown-4 and -5 (4a,b), and 1,3-alternate thiacalixarene-biscrown-5 and -6 (5a,b), depending on the metal carbonates and oligoethylene glycol ditosylates used. Starting from 1,3-dialkylated thiacalixarenes, the corresponding bridging reaction gave 1,3-alternate, partial-cone, and cone conformers 10−19, depending on the substituents present. Temperature-dependent studies revealed that the conformationally flexible 1,3-dimethoxythiacalixarene-crowns 10a−c exclusively occupy the 1,3-alternate conformation. Demethylation exclusively gave the cone 1,3-dihydroxythiacalixarene-crowns (3a,c), which could not be obtained by direct bridging of thiacalixarene. The different structures were assigned on the basis of several X-ray crystal structures and extensive 2-D 1H NMR studies.