Reaction of RuO₄ with carbon–carbon double bonds. Part 8.¹ Reaction of 7,8-didehydrocholesteryl acetate and cholesteryl acetate with RuO₄ and OsO₄. A comparative view

Abstract

The title reactions have been studied. The first formed compound from the oxidation of 7,8-didehydrocholesteryl acetate with RuO₄ performed in acetone–water (5∶1), both at room temperature and –70 °C, is the ruthenium(VI) diester 5. In mild acidic conditions compound 5 converts into the isomeric compound 6 that in turn is in equilibrium in the same conditions with a third isomeric ruthenium(VI) diester, 2, a compound previously isolated from the same oxidative process conducted at –70 °C. The structural relationship between the isomeric compounds 2, 5 and 6 has been established by careful spectral analyses and comparison of their NMR properties with those exhibited by the osmium-containing analogues (7 and 8) of the ruthenate esters 2 and 5, synthesized by reaction of 7,8-didehydrocholesteryl acetate with OsO₄ in dioxane. The RuO₄ oxidation of cholesteryl acetate at room temperature also furnishes two ruthenium(VI) diesters (9 and 10) structurally analogous to compounds 2 and 5. NMR evidence is reported that the Ru[double bond, length half m-dash]O and Os[double bond, length half m-dash]O groups possess similar magnetic anisotropy. The isomerization process involving the ruthenate esters of 7,8-didehydrocholesteryl acetate has also been studied by ¹H NMR spectroscopy and is briefly discussed.

References

1. For part 7 see ref. 7.
2. V. Piccialli, D. Sica and D. Smaldone, Tetrahedron Lett., 1994, 35, 7093.
3. D. G. Lee and M. van den Engh, The oxidation of organic compounds by RuO₄, in Oxidation in Organic Chemistry, ed. W. S. Trahanovsky, Academic Press, New York, 1973, vol. 5, part B, ch. 4.
4. A. Migliuolo, V. Piccialli and D. Sica, Tetrahedron, 1991, 47, 7937.
5. V. Piccialli, D. Smaldone and D. Sica, Tetrahedron, 1993, 49, 4211.
6. G. Notaro, V. Piccialli, D. Smaldone and D. Sica, Tetrahedron, 1994, 50, 4835.
7. L. Albarella, V. Piccialli, D. Smaldone and D. Sica, J. Chem. Res., 1996, (S) 400; (M) 2442.
8. K. B. Sharpless and K. Akashi, J. Am. Chem. Soc., 1976, 98, 1986.
9. T. K. M. Shing, E. K. W. Tam, V. W.-F. Tai, I. H. F. Chung and Q. Jiang, Chem. Eur. J., 1996, 2, 5057.
10. R. A. Johnson and K. B. Sharpless, in Catalytic Asymmetric Synthesis, ed. Iwao Ojima, VCH, Weinheim, 1993, pp. 227–272.
11. (a) P. O. Norrby, C. H. Kolb and B. K. Sharpless, Organometallics, 1994, 13, 344; (b) P. O. Norrby, C. H. Kolb and B. K. Sharpless, J. Am. Chem. Soc., 1996, 118, 35.
12. K. A. Jorgensen and R. Hoffmann, J. Am. Chem. Soc., 1986, 108, 1867.
13. (a) K. Tomioka, M. Nakajima and K. Koga, J. Am. Chem. Soc., 1987, 198, 6213; (b) K. Tomioka, M. Nakajima, Y. Itaka and K. Koga, Tetrahedron Lett., 1988, 29, 573; (c) K. Tomioka, M. Nakajima and K. Koga, J. Chem. Soc., Chem. Commun., 1989, 1921; (d) K. Tomioka, M. Nakajima and K. Koga, Tetrahedron Lett., 1990, 31, 1741.
14. (a) E. J. Corey, P. D. Jardine, S. Virgil, P.-W. Yuen and D. Connel, J. Am. Chem. Soc., 1989, 111, 9243; (b) E. J. Corey and G. I. Lotto, Tetrahedron Lett., 1990, 31, 2665; (c) E. J. Corey, M. C. Noe and S. Sarshar, J. Am. Chem. Soc., 1993, 115, 3828; (d) E. J. Corey and M. C. Noe, J. Am. Chem. Soc., 1993, 115, 12 579; (e) E. J. Corey, M. C. Noe and S. Sarshar, Tetrahedron Lett., 1994, 35, 2861; (f) E. J. Corey, M. C. Noe and M. J. Grogan, Tetrahedron Lett., 1994, 35, 6427; (g) E. J. Corey, A. Guzman-Perez and M. C. Noe, J. Am. Chem. Soc., 1994, 116, 12 109; (h) E. J. Corey, A. Guzman-Perez and M. C. Noe, J. Am. Chem. Soc., 1995, 117, 10 805; (i) E. J. Corey, A. Guzman-Perez and M. C. Noe, J. Am. Chem. Soc., 1995, 117, 10 817; (j) E. J. Corey and M. C. Noe, J. Am. Chem. Soc., 1996, 118, 319; (k) E. J. Corey, M. C. Noe and M. J. Grogan, Tetrahedron Lett., 1996, 37, 4899.
15. (a) U. Pidun, C. Boehme and G. Frenking, Angew. Chem., Int. Ed. Engl., 1996, 35, 2817; (b) A. Veldkamp and G. Frenking, J. Am. Chem. Soc., 1994, 116, 4937.
16. CHCl₃ was of analytical grade (99.5%; acidity 5 × 10 ^–3 meq g^–1).
17. J. K. H. Bridgemann, P. C. Cherry, A. S. Clegg, J. M. Evans, E. R. H. Jones, A. Kasal, V. Kumar, G. D. Meakins, Y. Morisawa, E. E. Richards and P. D. Woodgate, J. Chem. Soc. C, 1970, 250.
18. In all the ruthenate and osmate esters that we have so far studied, the carbons geminal to the metal resonated in the range 80–100 ppm.
19. In a previous work (L. Albarella, F. Giordano, M. Lasalvia, V. Piccialli and D. Sica, Tetrahedron Lett., 1995, 36, 5267) on the RuO₄ oxidation of α-pinene we hypothesized that ruthenium(VI) diesters possess a structure similar to that of osmium(VI) diesters in which the metal adopts a square-based pyramidal five-coordination.
20. 3β-Acetoxy-5-hydroxy-5α-cholestan-6-one and 5α-cholestane-3β,5, 6α-triol 3-acetate, the final oxidation products of cholesteryl acetate, were both present in the filtrate of the reaction mixture; their yields were as previously described (ref. 5).