Electronic effects in polyarylvinyl propellers. Solid state structures and dynamic behaviour in solution of several crowded enol derivatives

Abstract

By means of dynamic NMR (DNMR) investigations the dynamic behaviour of several crowded enol derivatives 5–11 and of the enols 12 and 13 has been studied. The NMR data are in agreement with the presence of vinyl propeller structures in solution, which fits the results of X-ray structural analysis. As deduced from a comparison with electrochemical data for the compounds investigated a severe electronic influence of the residue R attached at the enol ether oxygen atom on the rotation barriers can be ruled out. For Mes₂C[double bond, length half m-dash]C(Ph)OR systems, two different kinds of dynamic processes have been deduced on the basis of the DNMR data: first, an isolated rotation of the phenyl ring with a low activation barrier and, secondly, a correlated rotation of the two β-mesityl rings with a substantially higher barrier.

References

1. (a) R. Göttlich, B. C. Kahrs, J. Krüger and R. W. Hoffmann, Chem. Commun., 1997, 247; (b) J. Clayden, Angew. Chem., Int. Ed. Engl., 1997, 36, 949; (c) K. P. Meurer and F. Vögtle, Top. Curr. Chem., 1985, 127, 1.
2. (a) D. Gust and K. Mislow, J. Am. Chem. Soc., 1973, 95, 1535; (b) K. Mislow, Acc. Chem. Res., 1976, 9, 26; (c) J. P. Hummel, D. Gust and K. Mislow, J. Am. Chem. Soc., 1974, 96, 3679; (d) K. S. Hayes, M. Nagumo, J. F. Blount and K. Mislow, J. Am. Chem. Soc., 1980, 102, 2773.
3. (a) S. E. Biali and Z. Rappoport, J. Am. Chem. Soc., 1984, 106, 477; (b) S. E. Biali, D. A. Nugiel and Z. Rappoport, J. Am. Chem. Soc., 1989, 111, 846; (c) E. Schottland, J. Frey and Z. Rappoport, J. Org. Chem., 1994, 59, 1663 and refs. cited therein.
4. Z. Rappoport and S. E. Biali, Acc. Chem. Res., 1997, 30, 307.
5. R. J. Kurland, I. I. Schuster and A. K. Colter, J. Am. Chem. Soc., 1965, 87, 2279.
6. (a) M. Schmittel, M. Keller and A. Burghart, J. Chem. Soc., Perkin Trans. 2, 1995, 2327; (b) M. Schmittel, J.-P. Steffen and A. Burghart, Chem. Commun., 1996, 2349.
7. M. Schmittel and A. Langels, Angew. Chem., Int. Ed. Engl., 1997, 36, 392.
8. M. Schmittel, M. Keller and A. Burghart, unpublished results.
9. E. B. Nadler and Z. Rappoport, J. Am. Chem. Soc., 1987, 109, 2112.
10. A. Burghart, M. Schmittel and M. Keller, submitted for publication in J. Chem. Cryst.
11. W. Luef and R. Keese, Top. Stereochem., 1991, 20, 231.
12. H. S. Gutowsky and C. H. Holm, J. Chem. Phys., 1956, 25, 1228.
13. Z. Rappoport and S. E. Biali, Acc. Chem. Res., 1988, 21, 442.
14. A. Hoekstra and A. Vos, Acta Crystallogr., Sect. B, 1975, 31, 1716.
15. A. Mugnoli and M. Simonetta, J. Chem. Soc., Perkin Trans. 2, 1976, 1831.
16. For example, see see the propiophenone derived silyl enol ether [CH₃CH=C(Ph)O]₃SiCH₃; M. Schmittel, A. Burghart, W. Malisch, J. Reising and R. Söllner, J. Org. Chem., 1998, 63, 396.
17. E. B. Nadler, M. Röck, M. Schmittel and Z. Rappoport, J. Phys. Org. Chem., 1993, 6, 233.
18. D. A. Nugiel, S. E. Biali and Z. Rappoport, J. Am. Chem. Soc., 1984, 106, 3357.
19. E. Rochlin and Z. Rappoport, J. Org. Chem., 1994, 59, 3857.
20. C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165.
21. R. B. Nachbar, Jr., W. D. Hounshell, V. A. Naman, O. Wennerström, A. Guenzi and K. Mislow, J. Org. Chem., 1983, 48, 1227.
22. G. Yamamoto and M. Oki, Bull. Chem. Soc. Jpn., 1981, 54, 473, 481; G. Yamamoto and M. Oki, J. Org. Chem., 1983, 48, 1233.
23. S. E. Biali and Z. Rappoport, J. Org. Chem., 1986, 51, 2245.
24. D. A. Nugiel, S. E. Biali and Z. Rappoport, J. Am. Chem. Soc., 1984, 106, 3357.