Copper-catalyzed homolytic and heterolytic benzylic and allylic oxidation using tert-butyl hydroperoxide

Abstract

Allylic and benzylic alcohols were oxidized in good yields to the respective ketones by tert-butyl hydroperoxide (TBHP) in the presence of copper salts under phase-transfer catalysis conditions. This dehydrogenation was found to proceed via a heterolytic mechanism. CuCl₂, CuCl, and even copper powder were equally facile as catalysts, as they were all transformed in situ to Cu(OH)Cl which was extracted into the organic phase by the phase-transfer catalyst (PTC). Deuterium labeling experiments evidenced the scission of the benzylic C–H bond in the rate-determining step. Nonproductive TBHP decomposition was not observed in the presence of the alcohol substrates. Conversely, the oxygenation of π-activated methylene groups in the same medium was found to be a free radical process, and the major products were the appropriate tert-butyl peroxides. Catalyst deactivation, solvent effects, and extraction effects are discussed. By applying Minisci’s postulations concerning the relative reactivity of TBHP molecules towards tert-butoxyl radicals in protic and nonprotic environments, the coexistence of the homolytic and the heterolytic pathways can be explained. A complete reaction mechanism is proposed, wherein the free-radical oxidation obeys Kochi’s mechanism, and the heterolytic dehydrogenation is based on either a high-valent Cu^IV[double bond, length half m-dash]O species or a [Cu(OH)Cl]₂ species.

References

1. D. T. Sawyer, A. Sobkowiak and T. Matsushita, Acc. Chem. Res., 1996, 9, 409.
2. C. Walling, Acc. Chem. Res., 1998, 31, 155.
3. P. A. MacFaul, D. D. M. Wayner and K. U. Ingold, Acc. Chem. Res., 1998, 31, 159.
4. (a) For a monograph on oxidation reactions, see R. A. Sheldon and J. K. Kochi, Metal-Catalyzed Oxidations of Organic Compounds, Academic Press, New York, 1981; (b) for recent studies on the oxidation of allylic and benzylic alcohols, see K. P. Peterson and R. C. Larock, J. Org. Chem., 1998, 63, 3185 and refs. cited therein.
5. (a) H. H. Szmant, Organic Building Blocks of the Chemical Industry, Wiley, New York, 1989, pp. 386–391; (b) M. D. Clayton, Z. Marcinow and P. W. Rabideau, J. Org. Chem., 1996, 61, 6052.
6. (a) M. Nakayama, S. Shinke, Y. Matsushita, S. Ohira and S. Hayashi, Bull. Chem. Soc. Jpn., 1979, 52, 184; (b) W. G. Dauben, M. Lorber and D. S. Fullerton, J. Org. Chem., 1969, 34, 3587; (c) E. J. Parish, S. Chitrakorn and T.-Y. Wei, Synth. Commun., 1986, 16, 1371.
7. (a) K. B. Sharpless and T. R. Verhoeven, Aldrichim. Acta, 1979, 12, 63; (b) J. Muzart and A. Naît-Ajjou, J. Mol. Catal., 1991, 66, 155; (c) Synthesis, 1993, 785; (d) J. Muzart, Tetrahedron Lett., 1986, 27, 3139; (e) 1987, 28, 2131; (f) S. Uemura and S. R. Patil, Tetrahedron Lett., 1982, 23, 4353; (g) J. A. R. Salvador, M. L. Sa e Melo and A. S. C. Neves, Tetrahedron Lett., 1997, 38, 119.
8. (a) I. E. Marko, P. R. Giles, M. Tsukazaki, S. M. Brown and C. J. Urch, Science, 1996, 274, 2044; (b) J. Muzart, J. Mol. Catal., 1991, 64, 381.
9. (a) M. T. Rispens, C. Zondervan and B. L. Feringa, Tetrahedron: Asymmetry, 1995, 6, 661; (b) A. Levina and J. Muzart, Tetrahedron: Asymmetry, 1995, 6, 147; (c) Z.-R. Lu, Y.-Q. Yin and D.-S. Jin, J. Mol. Catal., 1991, 70, 391.
10. Preliminary communication: L. Feldberg and Y. Sasson, J. Chem. Soc., Chem. Commun., 1994, 1807.
11. cf. (a) R. A. Miller, W. Li and G. R. Humphrey, Tetrahedron Lett., 1996, 37, 3429; (b) M. Harre, R. Haufe, K. Nickish, P. Weinig, H. Weinmann, W. A. Kinney and X. Zhang, Org. Proc. Res. Dev., 1998, 2, 100; (c) G. Rothenberg, H. Wiener and Y. Sasson, J. Mol. Catal., 1998, 136, 251; (d) See also J. Muzart and A. Naît-Ajjou, in The Activation of Dioxygen and Homogenous Catalytic Oxidation, D. H. R. Barton, A. R. Martell and D. T. Sawyer, ed., Plenum Press, New York, 1993, p. 471.
12. For a monograph on the fundamentals of PTC, see C. M. Starks, C. L. Liotta and M. Halpern, Phase-Transfer Catalysis, Chapman and Hall, New York, 1994.
13. For a review on PTC extraction by hydrogen-bonding, see Y. Sasson and R. Neumann, in Handbook of Phase Transfer Catalysis, Y. Sasson and R. Neumann, ed., Chapman and Hall, London, 1997, pp. 510–546.
14. J. B. Sharkey and S. Z. Lewin, Thermochim. Acta, 1972, 3, 189.
15. I. W. C. E. Arends, K. U. Ingold and J. Lusztyk, J. Am. Chem. Soc., 1993, 115, 466.
16. Preliminary communication: L. Feldberg and Y. Sasson, Tetrahedron Lett., 1996, 12, 2063.
17. (a) J. K. Kochi, Tetrahedron, 1962, 18, 483; (b) J. Am. Chem. Soc., 1962, 84, 1572.
18. (a) F. Minisci, F. Fontana, S. Araneo, F. Recupero, S. Banfi and S. Quici, J. Am. Chem. Soc., 1995, 117, 226; (b) F. Minisci, F. Fontana, S. Araneo, F. Recupero and L. Zhao, Synlett, 1996, 119.
19. H. Paul, R. D. Small and J. C. Scaiano, J. Am. Chem. Soc., 1978, 102, 4520.
20. E. Napadensky and Y. Sasson, J. Chem. Soc., Chem. Commun., 1991, 65.
21. Similar transient high oxidation state copper species have been envisaged: (a) D. H. R. Barton, S. D. Bévière, W. Chavasiri, É. Csuhai and D. Doller, Tetrahedron, 1992, 48, 2895; (b) S.-I. Murahashi, Y. Oda, T. Naota and M. Komiya, J. Chem. Soc., Chem. Commun., 1993, 139.
22. J. Muzart and A. Naît-Ajjou, J. Mol. Catal., 1994, 92, 277.