Conformational studies of calix[5]arenes containing a single alkanediyl bridge †

Abstract

Six new calix[5]arenes substituted at one of the methylene bridges by methyl, ethyl, isopropyl, tert-butyl, p-tolyl and p-nitrophenyl have been synthesised by heat induced (3+2) fragment condensation of a linear trimer with the corresponding bishydroxymethylated alkanediyl diphenols in boiling xylene. These conditions give the calix[5]arenes more reliably in about 20–30% yield, while the corresponding condensation with bisbromomethylated alkanediyl diphenols leads to complex mixtures from which sometimes only a calix[8]arene could be isolated. In agreement with molecular mechanics calculations the calix[5]arenes prefer the cone conformation with an equatorial position of the alkyl or aryl substituent at the bridge. From variable temperature ¹H NMR spectroscopy the conformational equilibria and the energy barriers for the cone-to-cone ring inversion have been determined. Single crystal X-ray analyses have been performed for the calix[5]arene substituted by tert-butyl and for the corresponding tert-butyl substituted dinuclear precursor.

References

1. For a review on calixarenes see: V. Böhmer, Angew. Chem., 1995, 107, 785; Angew. Chem., Int. Ed. Engl., 1995, 34, 713.
2. Up to 20% are available by a one-pot reaction: D. R. Stewart and C. D. Gutsche, Org. Prep. Proc. Int., 1993, 25, 137 see also K. Iwamoto, K. Araki and S. Shinkai, Bull. Chem. Soc. Jpn., 1994, 67, 1499.
3. For example, the number of partially O-alkylated derivatives, as well as the number of potential conformational isomers in a completely O-alkylated product is higher than with calix[4]arenes.
4. D. R. Stewart, M. Krawieck, R. P. Kashyap, W. H. Watson and C. D. Gutsche, J. Am. Chem. Soc., 1995, 117, 586.
5. For recent examples of guest binding in the cavity of calix[5]arene derivatives see: (a) T. Haino, M. Yanase and Y. Fukazawa, Tetrahedron Lett., 1997, 38, 3739; (b) T. Haino, M. Yanase and Y. Fukazawa, Angew. Chem., 1998, 110, 1004; Angew. Chem., Int. Ed. Engl., 1998, 37, 997; (c) S. Pappalardo and M. F. Parisi, J. Org. Chem., 1996, 61, 8724; (d) R. Arnecke, V. Böhmer, R. Cacciapaglia, A. Dalla Cort and L. Mandolini, Tetrahedron, 1997, 53, 4901; (e) F. Arnaud-Neu, S. Fuangswasdi, A. Notti, S. Pappalardo and M. F. Parisi, Angew. Chem., 1998, 110, 120; (f) see also J. W. Steed, C. P. Johnson, R. K. Juneja, R. S. Burkhalter and J. L. Atwood, Supramol. Chem., 1996, 6, 235.
6. See for instance: (a) J. F. Gallagher, G. Ferguson, V. Böhmer and D. Kraft, Acta Crystallogr., Sect. C, 1994, 50, 73; (b) M. Perrin and S. Lecocq, J. Inclusion Phenom. Mol. Recognit. Chem., 1991, 11, 171.
7. (a) J. W. Steed, C. P. Johnson, C. L. Barnes, R. K. Juneja, J. L. Atwood, S. Reilly, R. L. Hollis, P. H. Smith and D. L. Clark, J. Am. Chem. Soc., 1996, 117, 11 426; (b) C. P. Johnson, J. L. Atwood, J. W. Steed, C. B. Bauer and R. D. Rogers, Inorg. Chem., 1996, 35, 2602.
8. J. M. Van Gelder, O. Aleksiuk and S. E. Biali, J. Org. Chem., 1996, 61, 8419.
9. S. E. Biali, V. Böhmer, S. Cohen, G. Ferguson, C. Grüttner, F. Grynszpan, E. F. Paulus, I. Thondorf and W. Vogt, J. Am. Chem. Soc., 1996, 118, 12 938.
10. G. Sartori, R. Maggi, F. Bigi, A. Arduini, A. Pastorio and C. Porta, J. Chem. Soc., Perkin Trans. 1, 1994, 1657.
11. M. Bergamaschi, F. Bigi, M. Lanfranchi, R. Maggi, A. Pastorio, M. A. Pellinghelli, F. Peri, C. Porta and G. Sartori, Tetrahedron, 1997, 53, 13 037.
12. K. No and K. M. Kwan, Synthesis, 1996, 1293.
13. Compare also T. Haino, T. Harano, K. Matsumura and Y. Fukazawa, Tetrahedron Lett., 1996, 36, 5793.
14. This downfield shift of the axial protons in the cone conformation of endo-calix[4]arenes is caused by the proximity to the OH groups, since in exo-calix[4]arenes the equatorial protons appear at lower field. See: S. E. Biali, V. Böhmer, J. Brenn, M. Frings, I. Thondorf, W. Vogt and J. Wöhnert, J. Org. Chem., 1997, 62, 8350.
15. F. A. L. Anet and V. J. Basus, J. Magn. Reson., 1978, 32, 339 For papers using this method see for example: S. P. Adams and H. W. Whitlock, J. Am. Chem. Soc., 1982, 104, 1602; D. Casarini, L. Lunazzi and D. Macciantelli, J. Chem. Soc., Perkin Trans. 2, 1985, 1839.
16. C. D. Gutsche and L. J. Bauer, J. Am. Chem. Soc., 1985, 107, 6052.
17. An unusually high energy barrier of 17.3 kcal mol^–1 was found for a “resorcinol derived” calix[5]arene consisting of five 2,4-dihydroxybenzophenone units: M. Tabatabai, W. Vogt, V. Böhmer, G. Ferguson and E. F. Paulus, Supramol. Chem., 1994, 4, 147.
18. This conformation can be designated as TTTtt(17.3), see I. Thondorf and J. Brenn, J. Chem. Soc., Perkin Trans. 2, 1997, 2293.
19. J. F. Gallagher, G. Ferguson, V. Böhmer and D. Kraft, Acta Crystallogr., Sect. C, 1994, 50, 73 and references cited there.
20. For a recent example with an average O⋯O-distance of 2.955 Å see: L. Dumazet, N. Ehlinger, F. Vocanson, S. Lecocq, R. Lamartine and M. Perrin, J. Inclusion Phenom. Mol. Recognit. Chem., 1997, 29, 175.
21. I. Thondorf, G. Hillig, W. Brandt, J. Brenn, A. Barth and V. Böhmer, J. Chem. Soc., Perkin Trans. 2, 1994, 2259.
22. (a) J. Gasteiger and M. Marsili, Tetrahedron, 1980, 36, 3219; (b) M. Marsili and J. Gasteiger, Croat. Chem. Acta, 1980, 53, 601.