NMR study of stereoelectronic anomeric and homoanomeric effects on the axial and equatorial CH bonds in 1,3-diazacyclohexanes and 1,5-diazabicyclo[3.2.1]octanes

Abstract

The ¹H and ¹³C NMR spectra of a series of 1,3-di-tert-butyl-1,3-diazacyclohexanes 6, and of 1,5-diazabicyclo[3.2.1]octanes 7, have been investigated in an attempt to find evidence regarding a stereoelectronic interaction of the non-bonding electron pairs on nitrogen or of the C–N bonding electron pairs in the ring, with the axial and equatorial CH bonds of the α- or β-methylene groups. In 6, the orbital carrying the non-bonding electron pair lies antiperiplanar to the axial α-CH bond; a significant n_N→σ*_CH 3-orbital interaction (the anomeric effect) is sterically possible, and this shows up in the values of δ_H and of ¹J_CH. In 7, the doubly-occupied orbital is orientated gauche to both the axial and equatorial α-CH bonds, and no anomeric effect is apparent. In 7 however, in contrast to 6, the stereochemistry is appropriate for a W-plan n_N→σ*_CH 4-orbital interaction with the equatorial β-CH bond, and comparison of the NMR data of 6 and 7 suggests that such a homoanomeric effect may operate, though it is much weaker than in the analogous 1,3-dioxanes. No evidence could be found for a σ_CN→σ*_CH 3-orbital interaction.

References

1. S. Wolfe, B. M. Pinto, V. Varma and R. Y. N. Leung, Can. J. Chem., 1990, 68, 1051 and references therein.
2. A. S. Perlin and B. Casu, Tetrahedron Lett., 1969, 2921.
3. A. J. Kirby, The Anomeric Effect and Related Stereoelectronic Effects at Oxygen, Springer-Verlag, Berlin, 1983.
4. M. Anteunis, D. Tavernier and F. Borremans, Bull. Soc. Chim. Blgs., 1966, 75, 396.
5. J. E. Anderson, A. J. Bloodworth, J. Cai, A. G. Davies and N. A. Tallant, J. Chem. Soc., Chem. Commun., 1992, 1689.
6. J. E. Anderson, A. J. Bloodworth, J. Cai, A. G. Davies and C. H. Schiesser, J. Chem. Soc., Perkin Trans. 2, 1993, 601.
7. J. Cai, A. G. Davies and C. H. Schiesser, J. Chem. Soc., Perkin Trans. 2, 1994, 1151.
8. E. Juaristi and G. Cuevas, Tetrahedron Lett., 1992, 33, 1847.
9. E. Juaristi, G. Cuevas and A. Flores-Vela, Tetrahedron Lett., 1992, 33, 6927.
10. E. Juaristi, G. Cuevas and A. Vela, J. Am. Chem. Soc., 1994, 116, 5796.
11. F. Bohlmann, Angew. Chem., 1957, 69, 641.
12. F. Bohlmann, Chem. Ber., 1958, 91, 2157.
13. J. P. Albrand, A. Cogne, D. Gagnaire and J. B. Robert, Tetrahedron, 1971, 27, 2453.
14. W. B. Jennings, D. R. Boyd, C. G. Watson, E. D. Becker, R. B. Bradley and D. M. Jerina, J. Am. Chem. Soc., 1972, 94, 8501.
15. Y. Takeuchi, P. J. Chivers and T. A. Crabb, J. Chem. Soc., Chem. Commun., 1974, 210.
16. R. R. Fraser and M. Bresse, Can. J. Chem., 1983, 61, 576.
17. T. A. Crabb and A. R. Katritzky, Adv. Heterocycl. Chem., 1984, 36, 1.
18. L. Carballeira, R. A. Mosquera and M. A. Rios, J. Molec. Struct., 1988, 176, 89.
19. R. A. Y. Jones, A. R. Katritzky and M. Snarey, J. Chem. Soc. (B), 1970, 131.
20. P. J. Halls, R. A. Y. Jones, A. R. Katritzky, M. Snarey and D. L. Trepanier, J. Chem. Soc. (B), 1971, 1320.
21. Y. Takeuchi, in Cyclic Organonitrogen Stereochemistry, ed. J. B. Lambert and Y. Takeuchi, VCH, New York, 1992.
22. A. R. Katritzky, V. J. Baker, F. M. S. Brito-Palma, I. J. Ferguson and L. Angiolini, J. Chem. Soc., Perkin Trans. 2, 1980, 1746.
23. R. W. Alder, E. Heilbronner, E. Honegger, A. B. McEwen, R. E. Moss, E. Olefirowicz, P. A. Petillo, R. B. Sessions, G. R. Weisman, J. M. White and Z.-Z. Yang, J. Am. Chem. Soc., 1993, 115, 6580.
24. R. F. Evans, Aust. J. Chem., 1967, 20, 1643.
25. R. Daniels and B. D. Martin, J. Org. Chem., 1962, 27, 178.
26. P. Poppelsdorf and R. C. Myerly, J. Org. Chem., 1961, 26, 131.
27. N. F. Curtis, Aust. J. Chem., 1986, 39, 239.