References
Luche, J. L. J. Am. Chem. Soc., 1978, 100, 2226.
The Luche reduction is the selective reduction of a ketone to an alcohol with the presence of lanthanides such as cerium (III) chloride and sodium borohydride. The solvent for this reaction is an alcohol that is usually methanol or ethanol. The cerium salt catalyst increases the electrophilicity of the carbonyl group leading to a 1, 2-addition while suppressing the competing 1,4-addition reaction. This selectivity occurs because sodium borohydride, also known as a “hard base” according to the HSAB theory, is fairly small with a highly charged state. The hydride attacks the electrophilic carbonyl and forms an alkoxide, completing the 1, 2-reduction. Conditions for this reaction do not affect carboxylic acids, esters, amides, halides, cyano and nitro groups. Even the compounds that are prone to undergo the 1, 4 addition reaction, such as 2-cyclopentenone, can lead to a 1, 2-addition selectivity with a high yield. These reactions may be conducted at room temperature, without any special conditions to exclude air or moisture.
3 Paper Citations
Kogl, M.; Brecker, L.; Warrass, R.; Mulzer, J. Angew. Chem. Int. Ed. 2007, 46, 9320-9322.
In the article, the researchers are trying to synthesize the biological compounds of pasteurestin A and pasteurestin B. Both are very useful in the veterinary sciences where they exhibit a strong antibacterial resistance against a pathogen for bovine respiratory disease. Under proper Luche conditions, intermediate 26 forms the diastereoselective alcohol intermediate 27 that ultimately leads to the pasteurestin B product.
Boyer, A.; Veitch, G. E.; Beckmann, E.; Ley, S. V. Angew. Chem. Int. Ed. 2009, 48, 1317-1320.
In this article, the researchers are synthesizing Azadirachtin, an insect antifeedant and growth inhibitor. Under Luche conditions, the desired intermediate alcohol 13 was formed from intermediate 9. The ratio increased when the temperature was lowered.
Brooke, D. G.; Morris, J. C. Tetrahedron Lett. 2008, 49, 2414-2417.
The researchers are synthesizing the natural product hydroxystrobilurin A. The authors used the Luche reduction to prevent a 1, 4-addition of hydride and select for a 1, 2-hydride addition in the intermediate.
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