Electrostatic repulsion by the charged tail of a radical controls the stereochemistry of coupling with anthracenide. Reversibility of benzylic fragmentation[hair space]1,2

(Note: The full text of this document is currently only available in the PDF Version )

Thomas Mall and Helmut Stamm


Abstract

Reaction of anthracenide A˙ with 1-pivaloyl-2,3-diphenylaziridines cis-4a and trans-4a yield the same products, namely PhCH2CHPhNHCOCMe3 (11) and AH–CHPhCHPhNHCOCMe3 (6) (AH = dihydroanthryl). The steric differentiation is lost when the two ketyls 12 formed from 4a undergo homolytic ring cleavage forming the same anionic radical 13. Extremely short reactions (⩽10 s) give 6 as the erythro isomer exclusively or nearly so. Coupling of 13 with A˙ does not form the precursor (threo-8) of threo-6 owing to electrostatic repulsion between A˙ and the anionic tail of 13 in the preferred conformation of the latter. Radical coupling is not completed within this short time so 11 can be formed directly from 13 via 10, the amide anion of 11. Reduction of 13 to carbanion 9 by outer-sphere electron transfer or via 8 and its benzylic fragmentation (BFR) is the other path to 11. Extending the time to 1 or 2 min has the following effects. Coupling of 13 with A˙ is completed at the expense of 11. Second, more than a trace of threo-6 is detected indicating that BFR 8→9 + A (A = anthracene) is reversible and that addition of dianion 9 to A proceeds without pronounced stereochemical preference. With even more time the erythrothreo ratio changes in favour of threo-6 and finally can even reach a value slightly less than 1. Simultaneously the amount of 11 increases slowly at the expense of the total 6 indicating that part of BFR which becomes irreversible by carbanion protonation 9 + THF→10. With much longer reaction times imidate ion 10 eliminates (E)-stilbene. Both isomers of 6 have been independently synthesized from the two isomers of 4a and anthracene hydride AH.


References

  1. Aziridines, Part 72; For Parts 70 and 71, see refs. 3 and 4.
  2. Arene Hydrides. Part 15; for Parts 13 and 14, see refs. 3 and 4.
  3. T. Mall and H. Stamm, J. Chem. Res., (S), 1996, 375 Search PubMed.
  4. T. Mall and H. Stamm, Pharmazie, 1996, 51, 831 Search PubMed.
  5. H. Stamm and R. Falkenstein, Chem. Ber., 1990, 123, 2227 CAS.
  6. M. Malissard, J.-P. Mazaleyrat and Z. Welvart, J. Am. Chem. Soc., 1977, 99, 6933 CrossRef CAS; E. Hebert, J.-P. Mazaleyrat, Z. Welvart, L. Nadjo and J.-M. Savéant, Nouv. J. Chim., 1985, 9, 75 Search PubMed.
  7. A. L. J. Beckwith and W. A. Waters, J. Chem. Soc., 1957, 1001 RSC.
  8. H. E. Zieger, I. Angres and L. Marasco, J. Am. Chem. Soc., 1973, 95, 8201 CrossRef CAS; S. Bank and J. F. Bank, Tetrahedron Lett., 1971, 4581 CrossRef CAS; Y.-J. Lee and W. D. Closson, Tetrahedron Lett., 1974, 1395 CrossRef CAS.
  9. P.-Y. Lin, K. Bellos, J. Werry, P. Assithianakis, R. Weiβ, T. Mall, G. Bentz and H. Stamm, J. Prakt. Chem., 1996, 338, 270 CrossRef CAS.
  10. A. W. Brinkmann, M. Gordon, R. G. Harvey, R. W. Rabideau and L. Stothers, J. Am. Chem. Soc., 1970, 92, 5912 CrossRef CAS; E. J. Panek and T. J. Rogers, J. Am. Chem. Soc., 1974, 96, 6921 CrossRef CAS.
  11. S. Bank and D. A. Juckett, J. Am. Chem. Soc., 1976, 98, 7742 CrossRef CAS.
  12. D. Archier-Jay, N. Besbes, A. Laurent, E. Laurent, S. Lesniak and R. Tardivel, Bull. Soc. Chim. Fr., 1993, 537.
  13. P.-Y. Lin, J. Werry, G. Bentz and H. Stamm, J. Chem. Soc., Perkin Trans. 1, 1993, 1139 RSC.
  14. T. Mall, B. Buchholz and H. Stamm, Arch. Pharm., 1994, 327, 377 Search PubMed.
  15. R. Falkenstein, T. Mall, D. Speth and H. Stamm, J. Org. Chem., 1993, 58, 7377 CrossRef CAS.
  16. R. Huisgen and H. Brade, Chem. Ber., 1957, 90, 1432 CAS; D. W. Farlow and R. B. Moodie, J. Chem. Soc. (B), 1970, 334 RSC.
  17. A. Sommer and H. Stamm, Liebigs Ann. Chem., 1992, 99 Search PubMed.
  18. P.-Y. Lin, K. Bellos, J. Werry, P. Assithianakis, R. Weiβ, T. Mall, G. Bentz and H. Stamm, J. Prakt. Chem., 1996, 338, 270 CrossRef CAS.
  19. H. Stamm, A. Sommer, A. Woderer, W. Wiesert, T. Mall and P. Assithianakis, J. Org. Chem., 1985, 50, 4946 CrossRef CAS.
Click here to see how this site uses Cookies. View our privacy policy here.