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Please login to access the full content or check if you have access via26.9.1.1.1.1 Variation 1: Allylic Oxidation with Stoichiometric Chromium Reagents
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Marsden, S. P., Science of Synthesis, (2005) 26, 1045.
The use of chromium(VI) species to perform allylic oxidations has been known since the 1950s. Early attempts focused on chromium(VI) oxide[1] or di-tert-butyl chromate,[2] but yields with these reagents are often variable. Chromium(VI) oxide–pyridine complex (Collins' reagent) in dichloromethane provides a more reproducible system,[3] while both pyridinium chlorochromate[4] and pyridinium dichromate[5] are also good reagents, often working best in benzene or dimethyl sulfoxide solution. These reactions are presumed to proceed via hydride abstraction to generate intermediates and hence mixtures of regioisomers are frequently observed where there is more than one site for hydride abstraction, as in the conversion of 1-methylcyclohexene (1) into a mixture of methylcyclohexenones 2 and 3 (Scheme 1).[3] Consistent with this observation, allylic methyl groups are relatively unreactive. The complex of chromium(VI) oxide with 3,5-dimethyl-1H-pyrazole is an excellent reagent for these transformations as demonstrated by the oxidation of cholesteryl ester 4 to enone 5.[6] The pyrazole is believed to participate in the oxidation mechanism, providing an explanation for the accelerations observed with this system over other reagents.
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Meeeeeeeeeee Meeeeeeee
(8β)-8-Meeeeeeeee-8-ee-8-ee Meeeeeee (8); Meeeeee Meeeeeeee:[8]
MMMMMMM: Meeeeeee(MM) eeeee eeee eeeeeeeee eee eeeeeeeeeee eeeeee eee ee eeeeeeeeee ee e eeeee eeeeeeeeee.
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References
| [1] | Meeeeeee, M. M.; Meeeeee, M. M., M. Me. Meee. Mee., (8888) 88, 888. |
| [2] | Meeeee, M. M.; Meeeeeee, M., M. Me. Meee. Mee., (8888) 88, 8888. |
| [3] | Meeeee, M. M.; Meeeee, M.; Meeeeeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
| [4] | Meeeee, M. M.; Meeeeeeeee, M.; Mee, M.-M., Meeee. Meeeee., (8888) 88, 8888. |
| [5] | Meeeee, M. M.; Mee, M.-M., Meeee. Meeeee., (8888) 88, 8888. |
| [6] | Meeeeee, M. M.; Meeee, M. M.; Meeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) M 88-8, 8888.
- 8.Meeeee-Meee, (8888) M 88e8, 88.
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