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Enantioselective ketone reductions convert prochiral ketones into chiral, non-racemic alcohols and are used heavily for the synthesis of stereodefined alcohols. [1]Carbonyl reduction, the net addition of H 2 across a carbon-oxygen double bond, is an important way to prepare alcohols.
Luche reduction is the selective organic reduction of α,β-unsaturated ketones to allylic alcohols. [ 1 ] [ 2 ] [ 3 ] The active reductant is described as "cerium borohydride", which is generated in situ from NaBH 4 and CeCl 3 (H 2 O) 7 .
Sodium triacetoxyborohydride is a milder reducing agent than sodium borohydride or even sodium cyanoborohydride. It reduces aldehydes but not most ketones. It is especially suitable for reductive aminations of aldehydes and ketones. [2] [3] [4]
Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, [5] is an inorganic compound with the formula Na B H 4 (sometimes written as Na[BH 4]). It is a white crystalline solid, usually encountered as an aqueous basic solution .
When an α,β-unsaturated carbonyl is reduced, three products can result: an allyl alcohol from simple carbonyl reduction, a saturated ketone or aldehyde resulting from 1,4‑reduction (also called conjugate reduction), or the saturated alcohol from double reduction. [19] Use of NaBH 4 can give any of these results, but InCl 3 or NiCl 2 ...
For the α,β unsaturated systems 10-12, efficient reduction of the ketone occurs despite the possible side reaction of hydroboration of the C-C unsaturated bond. The CBS reduction has also been shown to tolerate the presence of heteroatoms as in ketone 13 , which is capable of coordinating to the borane.
Aldehydes or ketones are reduced with sodium borohydride or lithium aluminium hydride (after an acidic workup). Another reduction using aluminium isopropoxide is the Meerwein-Ponndorf-Verley reduction. Noyori asymmetric hydrogenation is the asymmetric reduction of β-keto-esters.
The imine is then reduced to an amine by sodium cyanoborohydride. This reaction works on both aldehydes and ketones. The carbonyl can be treated with ammonia, a primary amine, or a secondary amine to produce, respectively, 1°, 2°, and 3° amines. [5] Aromatic ketones and aldehydes can be reductively deoxygenated using sodium cyanoborohydride. [6]