title: Synthesis and conformational evaluation of p-tert-butylthiacalix[4]arene-crowns.
abstract: 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 10-19, depending on the substituents present. Temperature-dependent studies revealed that the conformationally flexible 1,3-dimethoxythiacalix[4]arene-crowns 10a-c 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 (1)H NMR studies.
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology, Mesa Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Fijs W B
authors.initials: FW
authors.lastname: van Leeuwen
authors.forename: Hans
authors.initials: H
authors.lastname: Beijleveld
authors.forename: Huub
authors.initials: H
authors.lastname: Kooijman
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Willem
authors.initials: W
authors.lastname: Verboom
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt