Ketones alcohols, reduction

Carbon-carbon double bonds alkene to alkane reductions, trisubstituted alkenes, 40 ketone-alcohol reduction, 77, 86-87 a,p-unsaturated ester reduction, 93-96 Carbonyl compounds ... 

Deuterium-labeled organosilicon hydride alkene to alkane reductions, 34 disubstituted alkenes, 37-38 alkyl halide reduction, 29-31 Diastereoselectivity, ketone-alcohol reduction, 76-79... 

Halocarbons, ketone-alcohol reduction, 84 Halogenation, 4-methylbenzyl chloride [reductive halogenation of aldehyde to benzyl chloride], 124 Hemiacetals, reduction of, 97-99 Hemiaminals, reduction of, 99-100 Hemiketals, reduction of, 97-99 Heptene derivatives, alkene to alkane reductions, disubstituted alkenes, 36-38... 

Naphthoquinone, ketone-alcohol reduction, diastereoselectivity, 76-77 Nitrile reduction, a,/3-unsaturated nitriles, 96... 

S ilylation-intramolecular reduction, ketone-alcohol reduction, 78-79 Single-electron transfer (SET) process, alkyl halides and triflate reduction to alkanes, 28-31... 

Metal-ammonia solutions reduce conjugated enones to saturated ketones and reductively cleave a-acetoxy ketones i.e. ketol acetates) to the unsubstituted ketones. In both cases the actual reduction product is the enolate salt of a saturated ketone this salt resists further reduction. If an alcohol is present in the reaction mixture, the enolate salt protonates and the resulting ketone is reduced further to a saturated alcohol. Linearly or cross-conjugated dienones are reduced to enones in the absence of a proton donor other than ammonia. The Birch reduction of unsaturated ketones to saturated alcohols was first reported by Wilds and Nelson using lithium as the reducing agent. This metal has been used almost exclusively by subsequent workers for the reduction of both unsaturated and saturated ketones. Calcium has been preferred for the reductive cleavage of ketol acetates. 

The stereochemistry of reduction of 20-ketones with LiAlH4 is more influenced by substituents than that of other ketones. Usually reduction of the 20-ketone gives the more hindered -alcohol.208 stated that when C-17 has a substituent, the reduction yields almost quantitatively the 20)5-ol. However, the evidence on this point is conflicting Fukushima and Meyer claim that with a 17a-hydroxy present the 20a-ol is the predominant product except when an 11-ketone is being reduced simultaneously. Other results appear to support this conclusion, but... 

Conjugate addition of norpethidine (81) to benzoylethylene gives the ketone, 93. Reduction of the carbonyl group to the alcohol affords the potent analgesic phenoperidine (94). ... 

The reduction of piperitone to menthone cannot well be brought about by the action of sodium or of sodium-amalgam in alcoholic solution, because, with the latter particularly, a solid bimolecular ketone is formed at once. This is a finely crystallised substance, melts at 148° to 149° C., and has the formula C gHj O. Piperitone thus follows the rule with substances having a conjugated double bond, carvone for instance, also forms a bimolecular ketone on reduction, melting at 148° to 149° C. 

Prochiral aryl and dialkyl ketones are enantioselectively reduced to the corresponding alcohols using whole-cell bioconversions, or an Ir1 amino sulfide catalyst prepared in situ.695 Comparative studies show that the biocatalytic approach is the more suitable for enantioselective reduction of chloro-substituted ketones, whereas reduction of a,/ -unsaturated compounds is better achieved using the Ir1 catalyst. An important step in the total synthesis of brevetoxin B involves hydrogenation of an ester using [Ir(cod)(py) P(cy)3 ]PF6.696... 

Stereospecific ketone reduction was also observed (Giordano et al. 1985) with potassium, rubidium, and cesium (but not with sodium) in tertiary alcohols (but not in secondary or primary alcohols). The undesirable dimerization probably proceeds more readily in the case of sodium. Tertiary alcohols are simply more acidic than primary or secondary alcohols. It is reasonable to point out that the ketone-to-alcohol reduction of 3a-hydroxy-7-oxo-5p-cholic acid by alkali metals is a key step in the industrial synthesis of 3a,7p-dihydroxy-5p-cholic acid. 

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

Propyleine (104) also is derivable from ketone 437. Reduction of 437 with LAH gave the equatorial alcohol (438) which was converted into the corresponding mesylate (439). Clean elimination was effected by heating 439 with potassium carbonate in dimethylsulfoxide to yield a 3 1 mixture of propyleine (104) and isopropyleine (440) (Scheme 54) 455). 

Carboxylic acids are considerably less reactive than acid chlorides, aldehydes and ketones towards reduction. They cannot be reduced by catalytic hydrogenation or sodium borohydride (NaBH4) reduction. They require the use of a powerful reducing agent, e.g. LiAlH4. The reaction needs two hydrides (H ) from LiAlITj, since the reaction proceeds through an aldehyde, but it cannot be stopped at that stage. Aldehydes are more easily reduced than the carboxylic acids, and LiAltLj reduces all the way back to 1° alcohols. 

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