Influence of the size of upper and lower rim substituents on the fluxional and complexation behaviour of calix[5]arenes

A comparative study on a series of penta- O-alkylated p-H-calix[5]arenes 1b-e and p- tert-butylcalix[5]arenes 1g-m shows that the former are inherently mobile and adopt in solution non-cone conformations. The 1,2-alternate conformation for penta- O-benzyl ether 1c was proven by single-crystal X-ray...

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Bibliographic Details
Published in:Tetrahedron letters 1998-04, Vol.39 (14), p.1965-1968
Main Authors: Ferguson, George, Notti, Anna, Pappalardo, Sebastiano, Parisi, Melchiorre F., Spek, Anthony L.
Format: Article
Language:English
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Summary:A comparative study on a series of penta- O-alkylated p-H-calix[5]arenes 1b-e and p- tert-butylcalix[5]arenes 1g-m shows that the former are inherently mobile and adopt in solution non-cone conformations. The 1,2-alternate conformation for penta- O-benzyl ether 1c was proven by single-crystal X-ray analysis. VT-NMR studies on 1c-e have provided the first experimental evidence that conformational interconversion occurs via the p- phenyl- through- the- annulus mechanism with ΔG ‡ in the range 17.9–18.8 kcal mol −1. Unlike the corresponding tert-butylated counterparts, p-H-calix[5]arenes are unable to form 1:1 endo-calix complexes with primary unbranched alkylammonium cations. Graphic
ISSN:0040-4039
1873-3581
DOI:10.1016/S0040-4039(98)00106-3