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DOI: 10.1039/A902317H (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1999, 1601-1608

Irradiation of 5-azido-8-methoxypsoralen[hair space]† in water–acetonitrile gives nitrenium ion and triplet nitrene transients, but only nitrenium ion products

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Pratima Ramlall, Yuzhuo Li and Robert A. McClelland

Abstract

Irradiation of 5-azido-8-methoxypsoralen 10 in water–acetonitrile mixtures gives essentially quantitative yields of 5-imino-5,8-dihydropsoralen-8-one 17 regardless of the composition. This quinone imine is derived from the reaction of water with the nitrenium ion that results from protonation of the initially-formed singlet nitrene. Laser flash photolysis (LFP) in water and 90∶10 water–acetonitrile reveals a transient intermediate with λmax at 500–520 nm with the characteristics of a nitrenium ion, in particular a very effective quenching by azide ion. The immediate product of the reaction of water and the nitrenium ion is a hemiacetal; the breakdown of this species is also observed. In acetonitrile-rich solutions, the transient is a triplet nitrene (λmax at 410 nm), and at intermediate compositions, signals for both intermediates can be seen. Since the products are derived from the nitrenium ion, a mechanism is required where the triplet nitrene decays by way of this intermediate. Evidence that this actually happens is seen in an LFP experiment in water–2,2,2-trifluoroethanol (TFE). The decay of the nitrenium ion is slowed by the TFE, and the signal at 510 nm can be observed to grow at the same time as the signal for the triplet nitrene decays at 410 nm. Two mechanisms for the triplet nitrene→nitrenium conversion can be proposed, direct protonation or reversion to the singlet nitrene. The latter is favored because 0.02 mol dm–3 H+ has no effect on the rate constant for the decay of the triplet. This implies that the proton transfer step is already very fast with water as the acid, more consistent with the singlet nitrene as the species being protonated.

References

  1. G. B. Schuster and M. Platz, Adv. Photochem., 1992, 17, 143 Search PubMed.
  2. R. A. McClelland, P. A. Davidse and G. Hadzialic, J. Am. Chem. Soc., 1995, 117, 4173 CrossRef CAS.
  3. R. A. McClelland, M. J. Kahley, P. A. Davidse and G. Hadzialic, J. Am. Chem. Soc., 1996, 118, 4794 CrossRef CAS.
  4. P. Sukhai and R. A. McClelland, J. Chem. Soc., Perkin Trans. 2, 1996, 1529 RSC.
  5. J. Michalak, H. B. Zhai and M. Platz, J. Phys. Chem., 1996, 100, 14028 CrossRef CAS.
  6. R. Born, C. Burda, P. Senn and J. Wirz, J. Am. Chem. Soc., 1997, 119, 5061 CrossRef CAS.
  7. N. P. Gritsan, T. Yuzawa and M. S. Platz, J. Am. Chem. Soc., 1997, 119, 5059 CrossRef CAS.
  8. D. Ren and R. A. McClelland, Can. J. Chem., 1998, 76, 78 CrossRef CAS.
  9. P. Ramlall and R. A. McClelland, J. Chem. Soc., Perkin Trans. 2, 1999, 225 RSC.
  10. A. P. Dicks, A. Ahmad, R. D'Sa and R. A. McClelland, J. Chem. Soc., Perkin Trans. 2, 1999, 1 Search PubMed.
  11. T. A. Gadosy and R. A. McClelland, J. Am. Chem. Soc., 1999, 121, 1459 CrossRef CAS.
  12. H. Takeuchi, S. Hirayama, M. Mitani and K. Koyama, J. Chem. Soc., Perkin Trans. 2, 1986, 611 Search PubMed and references therein.
  13. R. A. Abramovitch, A. Hawi, J. A. R. Rodrigues and T. R. Trombetta, J. Chem. Soc., Chem. Commun., 1986, 283 RSC and references therein.
  14. A. Dipple, Carcinogenesis, 1995, 16, 437 CAS.
  15. R. A. McClelland, T. A. Gadosy and D. Ren, Can. J. Chem., 1998, 76, 1327 CrossRef CAS.
  16. R. A. McClelland, A. Ahmad, A. P. Dicks and V. E. Licence, J. Am. Chem. Soc., 1999, 121, 3303 CrossRef CAS.
  17. M. Novak, M. J. Kahley, E. Eiger, J. S. Helmick and H. E. Peters, J. Am. Chem. Soc., 1993, 115, 9453 CrossRef CAS.
  18. K. Feng and Y. Li, J. Org. Chem., 1996, 61, 398 CrossRef CAS.
  19. T. Chen, J. Michalak and M. S. Platz, Photochem. Photobiol., 1995, 61, 600 CAS.
  20. R. A. McClelland, Tetrahedron, 1996, 52, 6823 CrossRef CAS.
  21. R. A. McClelland, V. M. Kanagasabapathy, N. Banait and S. Steenken, J. Am. Chem. Soc., 1989, 111, 3966 CrossRef CAS.
  22. N. P. Gritsan, Z. Zho, C. M. Hadad and M. Platz, J. Am. Chem. Soc., 1999, 121, 1202 CrossRef CAS.
  23. M. B. Sullivan, K. Brown, C. J. Cramer and D. G. Truhlar, J. Am. Chem. Soc., 1998, 120, 11778 CrossRef CAS.
  24. G. B. Anderson, L. L. -N. Yang and D. E. Falvey, J. Am. Chem. Soc., 1993, 115, 7254 CrossRef CAS.
  25. S. Srivastava and D. E. Falvey, J. Am. Chem. Soc., 1995, 117, 10196.
  26. A. Albini, G. Bettinetti and G. Minoli, J. Am. Chem. Soc., 1991, 113, 6928 CrossRef CAS.
  27. A. Albini, G. Bettinetti and G. Minoli, J. Am. Chem. Soc., 1999, 121, 3104 CrossRef CAS.
  28. S. -J. Kim, T. P. Hamilton and H. F. Schaefer, J. Am. Chem. Soc., 1992, 114, 5349 CrossRef CAS.
  29. D. A. Hrovat, E. E. Waali and W. T. Borden, J. Am. Chem. Soc., 1992, 114, 8698 CrossRef CAS.
  30. A. A. Allen, A. J. Kresge, N. P. Schepp and T. T. Tidwell, Can. J. Chem., 1987, 65, 1719 CAS.
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