The tandem intermolecular Paternò–Büchi reaction: formation of tetrahydrooxepins

Abstract

The Paternò–Büchi reaction is the [2 + 2] photocycloaddition between carbonyl compounds and electron rich alkenes to generate oxetane products. By the introduction of substituted cyclopropyl rings to the alkene components, the utility of this reaction has been extended to facilitate the synthesis of substituted tetrahydrooxepins. It is proposed that initial addition of oxygen radicals to cyclopropyl enol ethers generates cyclopropylmethyl radicals which, when the cyclopropane ring bears appropriate radical-stabilising groups (e.g. phenyl, CO₂Et), undergo rapid fragmentation to form homoallylic 1,7-biradicals which then recombine to deliver the observed tetrahydrooxepin products. The importance of various radical-stabilising substituents on the efficiency of tetrahydrooxepin formation is examined.

References

1. E. Paterno and G. Chieffi, Gazz. Chim. Ital., 1909, 39, 341.
2. G. Büchi, C. G. Inman and E. S. Lipinsky, J. Am. Chem. Soc., 1954, 76, 4327.
3. G. S. Hammond and N. J. Turro, Science, 1963, 142, 1541.
4. J. S. Searles, ‘Oxetanes’, in Heterocyclic Compounds with Three- and Four-Membered Rings, Part 2, Interscience, 1964, p. 984.
5. J. A. Porco and S. L. Schreiber, ‘The Paternò–Büchi Reaction’, in Comprehensive Organic Synthesis, ed. B. M. Trost, Pergamon, New York, 1991, p. 151.
6. M. Bartok and K. L. Lang, ‘Oxiranes’, in Small Ring Heterocycles (Part 3), ed. A. Hassner, Wiley, New York, 1964, p. 89.
7. D. S. Watt, S. Vasudevan, P. Brock and H. Morita, J. Org. Chem., 1994, 59, 4677.
8. T. Bach and K. Jödicke, Chem. Ber., 1993, 126, 2457.
9. T. Bach, Tetrahedron Lett., 1994, 35, 5845.
10. H. A. J. Carless, J. Beanland and S. Mwesigye-Kibende, Tetrahedron Lett., 1987, 28, 5933.
11. G. I. Jones, ‘Synthetic Applications of the Paternò–Büchi Reaction’, in Organic Photochemistry, ed. A. Padwa, Marcel Dekker, New York, 1981, p. 2.
12. W. Horspool and D. Armesto, Organic Photochemistry: A Comprehensive Treatment, Prentice Hall, London, 1992.
13. G. Büchi, J. T. Kofron, E. Koller and D. Rosenthal, J. Am. Chem. Soc., 1956, 78, 876.
14. M. Yamaguchi and I. Hirao, Tetrahedron Lett., 1984, 25, 4549.
15. M. Sevrin and A. Krief, Tetrahedron Lett., 1980, 21, 585.
16. D. R. Arnold, ‘The Photocycloaddition of Carbonyl Compounds to Unsaturated Systems: The Synthesis of Oxetanes’, in Advances in Photochemistry, ed. W. A. Noyes, G. S. Hammond and J. N. Pitts, Interscience, New York, 1968, p. 301.
17. S. Nishida, N. Shimizu, M. Ishikawa and K. Ishikura, J. Am. Chem. Soc., 1974, 96, 6456.
18. P. J. Wagner and K. L. Cheng, J. Am. Chem. Soc., 1994, 116, 7945.
19. D. C. Neckers and S. Hu, J. Org. Chem., 1997, 62, 755.
20. D. C. Nonhebel, Chem. Soc. Rev., 1993, 347.
21. E. J. Corey and M. Chaykovsky, J. Am. Chem. Soc., 1965, 87, 1353.
22. H. Hagiwara, F. Abe and H. Uda, J. Chem. Soc., Perkin Trans. 1, 1993, 2651.
23. M. W. Majchrzak and A. Kotelko, Synthesis, 1983, 469.
24. H. M. Walborsky and F. M. Hornyak, J. Am. Chem. Soc., 1955, 77, 6026.
25. F. J. Impastato and H. M. Walborsky, J. Am. Chem. Soc., 1962, 84, 4838.
26. T. Bach, Liebigs Ann./Recueil, 1997, 1627.
27. A. G. Griesbeck and S. Stadtmüller, J. Am. Chem. Soc., 1991, 113, 6923.
28. J. N. Lambert, C. Y. Gan and R. W. Gable, Acta Crystallogr., 1997, C53, 1122.
29. A. E. Derome, Modern NMR Techniques for Chemistry Research, Pergammon, London, 1987.
30. W. C. Still, M. Kahn and A. Mitra, J. Org. Chem., 1978, 43, 2923.
31. D. D. Perrin and W. L. F. Armarego, PuriWcation of Laboratory Chemicals, Pergamon, Sydney, 1986.
32. P. A. Grieco and Y. Ohfune, J. Org. Chem., 1978, 43, 2720.
33. R. M. Roberts, R. G. Landolt, R. N. Greene and E. W. Heyer, J. Am. Chem. Soc., 1967, 89, 1404.
34. J. Baluenga, P. L. J. Bernad, J. M. Concellon, A. Pinera-Nicholas and S. Garcia-Granda, J. Org. Chem., 1997, 62, 6870.
35. B. K. Carpenter, R. H. Newman-Evans and R. J. Simon, J. Org. Chem., 1990, 55, 695.
36. H. O. House, A. V. Prabhu, J. M. Wilkins and L. F. Lee, J. Org. Chem., 1976, 41, 3067.