· Chromyl Acetate
· (MW 202.10)
(oxidizing agent for carbon-hydrogen bonds, carbon-carbon double bonds, macrocyclic lactones, and alcohols)
Physical Data: mp 30.5 °C.
Solubility: sol CCl4, Ac2O, HOAc; slowly oxidizes many solvents.
Purification: spectrophotometrically or titrimetrically.2-5
Preparative Methods: prepared in situ from CrO3 and Ac2O or Ac2O/HOAc. Slow addition of CrO3 to a cooled solution of Ac2O is recommended in order to avoid a highly exothermic reaction.
Handling, Storage, and Precautions: best results are obtained from the freshly prepared oxidant. Chromium compounds are toxic and should be handled with care and disposed of in conformance with established procedures. This reagent should be handled in a fume hood.
This powerful oxidant, which is sometimes called chromium(VI) oxide-acetic anyhdride or chromium(VI)-acetic anhydride-acetic acid, oxidizes carbon-hydrogen bonds in bicycloalkanes and polycycloalkanes to form alcohols and ketones.6-12 The initially formed alcohol may also be acetylated or oxidized to the ketone in the reaction mixture. Methylbenzenes are oxidized to the corresponding benzoic acids12 and, in the presence of sulfuric acid (Thiele reagent), benzylidene diacetates (aldehyde precursors) are obtained.13-15 Alkenes are oxidized to oxiranes16-18 and diol carbonates.19 Diarylmethanes and secondary alcohols are oxidized to ketones.12,20
Oxidation of Carbon-Hydrogen Bonds to Form Alcohols and Ketones.
Chromyl acetate oxidizes bicyclo[2.2.1]heptane (1) to (2) and (3) (eq 1),6 bicyclo[2.2.2]octane (4) to (5) and (6) (eq 2),6 and adamantane (7) to (8) and (9) (eq 3).6 Tricyclo[18.104.22.168.2,6]octane (10) is oxidized to (11) and (12) in a 9:1 ratio (eq 4).7 (-)-Isobornyl acetate (13) is regioselectively oxidized to (14) and (15) (4:1; eq 5), which is useful in the synthesis of nojigku acid.8 Similarly, (-)-bornyl acetate (16) is oxidized to (17) and (18) (eq 6).9 3b-Acetoxy-5a,6b-dichloroandrostan-17-one
(19) is oxidized by chromyl acetate to the corresponding 14a-hydroxy compound (20) (eq 7)10 and 3,5a-cycloandrostane is oxidized to a mixture of three ketones.11 The latter reaction involves oxidation and carbonyl formation a to a cyclopropane ring.
Oxidation of Benzylic Carbon-Hydrogen Bonds to Alcohols, Aldehydes, Carboxylic Acids, and Ketones.
Chromyl acetate in the presence of sulfuric acid converts methyl-substituted aromatic and heteroaromatic compounds to the corresponding benzylidene diacetates in fair to excellent yields (eq 8).13-15 The benzylidene diacetates are easily hydrolyzed to aldehydes. Diphenylmethane and triphenylmethane are oxidized to benzophenone and triphenylcarbinol, respectively, in near quantitative yields.12
Oxidation of Carbon-Carbon Double Bonds to Oxiranes.
Chromyl acetate16-18 and chromyl nitrate19 stereospecifically oxidize carbon-carbon double bonds to oxiranes (eq 9). Tetraphenylethylene is converted to the oxirane, benzophenone, and benzopinacol (eq 10).20
Unlike the Dipyridine Chromium(VI) Oxide complex and Pyridinium Chlorochromate which gave nearly exclusive a-oxidation of alkynes, chromyl acetate oxidized the a-position and the triple bond.21 Macrocyclic lactones are oxidized to monoketo lactones with some regioselectivity. The preferred conformation of the lactone probably influences the site of oxidation.22 New oxygenated derivatives of 1,8-epoxy-p-menthane were obtained by the chromyl acetate oxidation of 1,8-cineole.23
- 1. (a) Wiberg, K. B. In Oxidation in Organic Chemistry; Wiberg, K. B., Ed.; Academic: New York, 1965; Part A, pp 131-135. (b) Freeman, F. In Organic Synthesis By Oxidation With Metal Compounds; Mijs, W. J.; de Jonge, C. R. H. I., Eds.; Plenum: New York, 1986; Chapter 2. (c) Lee, D. G. The Oxidation of Organic Compounds by Permanganate Ion and Hexavalent Chromium, Open Court: La Salle, IL, 1980. (d) Stewart, R. Oxidation Mechanisms: Applications to Organic Chemistry, Benjamin: New York, 1964. (e) Cainelli, G.; Cardillo, G. Chromium Oxidations in Organic Chemistry, Springer: Berlin, 1984. (f) Krauss, H.-L. AG 1958, 70, 502.
- 2. Freeman, F.; Armstead, C. R.; Essig, M. G.; Karchefski, E. M.; Kojima, C. J.; Manopoli, V. C.; Wickman, A. H. CC 1980, 65.
- 3. Kapoor, R.; Sharma, R.; Kapoor, P. ZN(B) 1984, 39B, 1702.
- 4. (a) Enqvist, E. Ann. Acad. Sci. Fenn., Ser. A2 1977, 183. (b) Lepse, P. Ph. D. Thesis, 1962, Yale University, New Haven, CT.
- 5. Sowinska, M.; Myrzczek, J.; Bartecki, A. J. Mol. Struct. 1990, 218, 267.
- 6. Bingham, R. C.; Schleyer, P. v. R. JOC 1971, 36, 1198.
- 7. Meinwald, J.; Kaplan, B. E. JACS 1967, 89, 2611.
- 8. Darby, N.; Lamb, N.; Money, T. CJC 1979, 57, 742.
- 9. Allen, M. S.; Darby, N.; Salisbury, P.; Sigurdson, E. R.; Money, T. CJC 1979, 57, 733.
- 10. Sykes, P. J.; Kelly, R. W. JCS(C) 1968, 2346.
- 11. Beugelmans, R.; Toubiana, B. E. CR(C) 1967, 264, 343.
- 12. Freeman, F.; Bond, D. L.; Freeman, Jr., W. L.; Karchefski, E. M. Unpublished data.
- 13. Thiele, J.; Winter, E. LA 1900, 311, 353.
- 14. Nishimura, T. OSC 1963, 4, 713.
- 15. Freeman, F.; Karchefski, E. M. CED 1977, 22, 355.
- 16. Hickinbottom, W. J.; Moussa, G. E. M. JCS 1957, 4195.
- 17. Moussa, G. E. M.; Eweiss, N. F. J. Appl. Chem. 1969, 19, 313.
- 18. Moussa, G. E. M.; Abdalla, S. O. J. Appl. Chem. 1970, 20, 256.
- 19. Miyaura, N.; Kochi, J. K. JACS 1983, 105, 2368.
- 20. Mosher, W. A.; Steffgen, F. W.; Lansbury, P. T. JOC 1961, 26, 670.
- 21. Sheats, W. B.; Olli, L. K.; Stout, R.; Lundeen, J. T.; Justus, R.; Nigh, W. G. JOC 1979, 44, 4075.
- 22. Eigendorf, G. K.; Ma, C.-L.; Money, T. CC 1976, 561.
- 23. De Martinez, M. V.; De Venditi, F. G.; De Fenick, I. J. S.; Catalan, C. A. N. An. Asoc. Quim. Argent. 1982, 70, 137 (CA 1982, 96, 218 042).
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