Further insight via¹⁵N NMR spectroscopy into the reactive intermediates formed by superacid protonation of crowded nitro-PAHs: persistent dihydroxyiminiumpyrenium and hydroxyiminiumpyrenium dications

Abstract

Low temperature protonation of 1-nitropyrene and its ¹⁵N-labelled isotopomer with FSO₃H·SbF₅ (1∶1) (‘magic acid’)–SO₂ClF (or SO₂) or with FSO₃H·SbF₅ (4∶1)–SO₂ClF generates either the dihydroxyiminiumpyrenium dication (NO₂ diprotonation) or the hydroxyiminiumpyrenium dication as the principle NMR observable persistent species (depending on the sample concentration, reaction time and the superacid). The latter is independently generated by diprotonation of authentic 1-nitrosopyrene. Variable formation of dihydroxyiminiumpyrenium and hydroxyiminiumpyrenium dications is also observed in the protonation of sterically crowded 1-nitro-2,7-di-tert-butylpyrene, which gives the corresponding dihydroxyiminiumpyrenium dication in FSO₃H·SbF₅ (1∶1)–SO₂ClF (or SO₂) and the hydroxyiminiumpyrenium dication by low temperature reaction with FSO₃H·SO₂ClF or CF₃SO₃H·SO₂. Protonation of the buttressed 1-nitro-2,4,6,8,10-pentaisopropylpyrene and its ¹⁵N-labelled isotopomer produces the dihydroxyiminiumpyrenium dication (no NMR evidence for the formation of the hydroxyiminiumpyrenium dication) which, as shown before (J. Chem. Soc., Perkin Trans. 2, 1995, 537), undergoes a facile cyclization to the oxazoline-fused pyrenium cation for which ¹⁵N NMR data are now presented. Diprotonation and subsequent cyclization of the singly ¹⁵N-labelled 1,3-dinitro-2,4,6,8,10-pentaisopropylpyrene are also studied. Whereas our work reaffirms the generality of NO₂ diprotonation in nitropyrenes, it focuses attention on an additional pathway leading to [double bond, length half m-dash]NH(OH) dication formation.

PM3 calculations are used as a complementary tool to examine the geometries and energies of the resulting dications.

References

1. P. Upadhaya, L. S. von Tunglen, P. P. Fu and K. El-Bayoumy, Chem. Res. Toxicol., 1994, 7, 690.
2. B. P. Cho, Org. Prep. Proced. Int., 1995, 27, 243.
3. K. Fukuhara, M. Takei, H. Kageyama and N. Miyata, Chem. Res. Toxicol, 1995, 8, 47.
4. D. Herrerno-Saez, F. E. Evans and P. P. Fu, Chem. Res. Toxicol., 1994, 7, 806.
5. W. A. Vance and R. Chan, Environ. Mutagen., 1983, 5, 859.
6. P. P. Fu, Y.-C. Ni, Y.-M. Zhang, R. H. Heflich, Y.-X. Wang and J.-S. Lai, Mutat. Res., 1989, 225, 121.
7. S.-T. Lin, Y.-F. Jih and P. P. Fu, J. Org. Chem., 1996, 61, 5271.
8. B. P. Cho, M. Kim and R. G. Harvey, J. Org. Chem., 1993, 58, 5788.
9. A. M. van den Braken van Leersum, J. Cornelisse and J. Lugtenburg, Tetrahedron Lett., 1985, 4823.
10. Y.-S. Yu, J.-S. Lai and P. P. Fu, J. Org. Chem., 1993, 58, 7283.
11. K. Fukhari, M. Takei, H. Kageyama and N. Miyata, Chem. Res. Toxicol., 1994, 7, 357.
12. F. E. Evans, J. Deck and P. C. Howard, Chem. Res. Toxicol., 1994, 7, 357.
13. A. M. Dietrich, C. R. Guenat and L. M. Ball, Abstracts of 35th ASMS conference on Mass Spectrometry and Allied Topics, Denver, CO, May 1987.
14. Review: K. K. Laali, Chem. Rev., 1996, 96, 1873.
15. K. K. Laali, S. Hollenstein, R. G. Harvey and P. E. Hansen, J. Org. Chem., 1997, 62, 5804.
16. K. K. Laali and P. E. Hansen, J. Org. Chem., 1997, 62, 5804.
17. K. K. Laali, M. Tanaka, S. Hollenstein and M. Cheng, J. Org. Chem., 1997, 62, 7752.
18. K. K. Laali, S. Hollenstein and P. E. Hansen, J. Chem. Soc., Perkin Trans. 2, 1997, 2207.
19. K. K. Laali, S. Bolvig and P. E. Hansen, J. Chem. Soc., Perkin Trans. 2, 1995, 537.
20. K. K. Laali, T.-M. Liang and P. E. Hansen, J. Org. Chem., 1992, 57, 2658.
21. J. V. Bullen, J. H. Ridd and O. Sabek, Gazz. Chim. Ital., 1990, 120, 291.
22. J. V. Bullen and J. H. Ridd, J. Chem. Soc., Perkin Trans. 2, 1990, 1681.
23. R. P. Austin and J. H. Ridd, J. Chem. Soc., Perkin Trans. 2, 1994, 1411.
24. R. P. Austin and J. H. Ridd, J. Chem. Soc., Perkin Trans. 2, 1993, 1229.
25. G. A. Olah and D. J. Donovan, J. Org. Chem., 1978, 43, 1743.
26. S. Berger, S. Braun and H.-O. Kalinowski, ¹⁵N NMR Spectroscopie, Thieme Verlag, Stuttgart, 1992, vol. 2.
27. D. J. Craik, G. C. Levery and R. T. C. Brownlee, J. Org. Chem., 1983, 48, 1601.
28. G. J. Martin, M. L. Martin and J.-P. Gouesnard, ¹⁵N NMR Spectroscopy, in NMR Basic Principles and Progress, ed. P. Diehl, E. Fluck and R. Kosfeld, 1981.
29. T. Ohta, K. Shudo and T. Okomoto, Tetrahedron Lett., 1984, 25, 325.
30. Nitrogen NMR, ed. M. Witanowski and G. A. Webb, Plenum, London, 1973.
31. I. Yavari, R. E. Botto and J. D. Roberts, J. Org. Chem., 1978, 43, 2542.
32. G. C. Levy and R. L. Lichter, Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy, Wiley Interscience, New York, 1979.
33. (a) K. K. Laali and D. S. Nagvekar, J. Org. Chem., 1991, 56, 1867; (b) K. K. Laali and J. J. Houser, J. Phys. Org. Chem., 1992, 5, 244.