Conformational properties of propargyloxy-calix[4]arene tricarboxamides: NMR and DFT studies on the O-through-the-annulus rotation

Abstract

The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R¹ on the conformational inversion was investigated by means of ¹H NMR. The rotational isomerisation of the parent (R¹ = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies.

Keywords::

• calix[4]arene
• propargyloxy group rotation
• partial cone
• 1,2-alternate
• conformational equilibrium

Acknowledgements

The authors are grateful to K. Tarcsay-Petrov and M. Bojtár for fruitful discussions and suggestions during the preparation of the manuscript.

Notes

^1. Present affiliation: XiMo Hungary Ltd., Pusztaszeri út 59-67, Budapest 1025, Hungary.

Additional information

Funding

This work was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TÁMOP 4.2.4. A/-11-1-2012-0001 ‘National Excellence Program’, the Hungarian Scientific Research Fund [grant number OTKA K 67585] and Richter Gedeon Centenary Foundation [J.B.Cz.'s fellowship].