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Venturello, P.; Barbero, M., Science of Synthesis, (2006) 8, 883.
Reduction of 9-oxo-α-agarofuran with sodium in liquid ammonia in the presence of excess ethanol affords, almost quantitatively, the corresponding equatorial 9α-alcohol. In the absence of an added proton donor, reduction of 9-oxo-α-agarofuran gives the equatorial 9α-alcohol and the axial 9β-alcohol in the ratio 14:42.[6] Similarly, the reduction of 3α-hydroxy-5β-7-oxocholanic acid carried out using a large excess of sodium in alcohols, provides 3α,7β-dihydroxy-5β-cholanic acid and 3α,7α-dihydroxy-5β-cholanic acid in a ratio from 80:20 to 85:15 in almost quantitative yield.[7,8] In order to increase the stereoselectivity toward the formation of the 7β-isomer, the factors that influence the stereochemistry of this reduction have been investigated.[9] Higher stereoselectivity (95:5) has been observed when the reduction is carried out with sodium in 2-methylbutan-2-ol or tert-butyl alcohol, in the presence of potassium, rubidium, or cesium 2-methylbutan-2-olates. The reduction of (+)-camphor (3) using alkali metals in tetrahydrofuran with sonication[10] (Scheme 3) has also been reported; the reaction gives a ratio of endo-borneol (4A) and exo-borneol (4B) essentially identical to that obtained with sodium metal in ammonia.[11]
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References
[6] | Meeeeee, M. M.; Meeee, M. M.; MeMeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
[7] | Meeeeeeeee, M., Meee Meee. Meeee., (8888) 88, 88. |
[8] | Meeeeeee, M.; Meeeeeeee, M.; Meeeeeee, M.; Meeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[9] | Meeeeeee, M.; Meeeeeeee, M.; Meeeeeee, M., Meeee. Meee., (8888) 88, 888; Meeee. Meee. Mee. Me. Meee., (8888) 88, 888. |
[10] | Meeeeee, M. M.; Meee, M.-M.; Meeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[11] | Meeeeeeeeeeee, M.; Meeeeeee, M.; Meeeeee, M.; Meeeee, M., Meee. Meee. Meee, (8888) 88, 8888. |
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- 8.Meeeee-Meee, (8888) 8/8e, 888.
- 8.Meeeee-Meee, (8888) 8/8e, 888.