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'Conformational Isomers' in keywords Facet   section ZfN Section B:Volume 053  [X]
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1998 (1)
1Author    Ion Neda, Tjark Siedentop, Alexander Vollbrecht, Holger Thönnessen, PeterG. Jones, Reinhard SchmutzlerRequires cookie*
 Title    A New Synthesis of Tetrakis(C-methyl)octakis(hydroxyethyl)calix[4]- resorcinarene via an Ethoxy-Tethered Trimethylsiloxy Precursor  
 Abstract    The octakis(trimethylsiloxy)calix[4]resorcinarenes, 3 and 4, were synthesized by reaction of 1 and its tetrabromo derivative 2 with hexamethyldisilazane, and were found to exhibit dynamic behaviour in solution. Temperature-dependent NMR investigations confirmed the presence of at least two conformational isomers of 3 in solution. The conformation of 3 in the solid state was determined by an X-ray crystal structure analysis; the calixarene displays a boat conformation. The introduction of the ethoxy group as a spacer into the molecule of 1 was ef­ fected via its reaction with ethyl bromoacetate and subsequent reduction with lithium alu­ minium hydride forming the ethoxy-tethered C-methylcalix[4]resorcinarene 6 in an impure state. Reaction of crude 6 with hexamethyldisilazane furnished the ethoxy-tethered oc-takis(trimethylsiloxy)calix[4]resorcinarene 7; its hydrolysis led to pure 6. Calixresorcinarenes display interesting proper­ ties as materials and as complexing agents. Their use in the synthesis of cavitands and (hemi)carcerands [5], as building blocks in the preparation of phosphorus-functionalized calix[4]resorcinarenes [6], and their application as a fascinating class of container molecules [7, 8] have been described. We are now presenting the synthesis and char­ acterization in a pure state of the polyol deriva­ tive 6, related to calix[4]resorcinarene, with none of the eight hydroxy groups bonded directly to the aromatic ring system, but via OCH2CH2 groups as spacers. The synthesis of 6 in an impure state from calix[4]resorcinarene and ethylene oxide has been described [9]. No direct characterization of 6 has been reported; rather, it was converted to an octaacetate. Recently, the preparation of the C-undecyl-octakis-hydroxyethyl derivative of the latter has been described, functioning as an in­ termediate in the synthesis of macrocyclic sugar clusters [ 10]. An X-ray crystal structure determination of 3, bearing eight trimethylsiloxy groups directly bonded to the upper rim of the molecule, was con­ ducted. The results are compared with regard to conformational aspects to those of the correspond­ ing octakis(ethoxy-tethered) trimethylsiloxy deriva­ tive 7. 
  Reference    Z. Naturforsch. 53b, 841—848 (1998); received February 18 1998 
  Published    1998 
  Keywords    Calix[4]resorcinarenes, Conformational Isomers, Spacer Groups, X-Ray Data 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0841.pdf 
 Identifier    ZNB-1998-53b-0841 
 Volume    53