Aliphatic ketone reduction

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction is essentially a Knoevenagel reaction, though it is usually also called a Tollens reaction ... 

Accordingly, ATH is a versatile method for the enantioselective reduction of prochiral aromatic ketones. Aliphatic unconjugated ketones, however, are only reduced in poor to moderate enantioselec-tivities up to date (33-36). 

Reduction of ketones.1 Reduction of one carbonyl group requires 2 moles of this complex because B2H6 is also released. Aliphatic ketones are reduced readily, but aromatic ketones are reduced much more slowly, and a,(3-enones even more slowly. Consequently some selective reductions are possible. 

When aliphatic nitro compounds are used instead of aldehydes or ketones, no reduction occurs, and the reaction has been referred to as a Tollens reaction (see 16-43). However, the classical condensation of an aliphatic nitro compound with an aldehyde or ketone is usually called the Henry reaction or the Kamlet reaction, and is essentially a nitro aldol reaction. A variety of conditions have been reported, including the use of a silica catalyst, Mg—A1 hydrotalcite, a tetraalkylam-monium hydroxide,proazaphosphatranes, " or an ionic liquid.A solvent free Henry reaction was reported in which a nitroalkane and an aldehyde were reacted on KOH powder. Potassium phosphate has been used with nitromethane and aryl aldehydes. The Henry reaction has been done using ZnEt2 and 20%... 

A complex Zn(BH4)2-1.5 DMF has been described [HJl]. This shows a greater selectivity than Zn(BH4)2 in diethylether and does not react with the a-enones. In MeCN, this complex allows the reduction of aldehydes in the presence of ketones, the reduction of some sterically unhindered ketones in the presence of other less accessible ketones, or even the reduction of aliphatic ketones in the presence of aromatic ones (Section 3.2.1). 

Schiff s reagent An aqueous solution of magenta dye decolorized by reduction with sulfur(IV) oxide. It is a test for aldehydes and ketones. Aliphatic aldehydes restore the color quickly aliphatic ketones and aromatic aldehydes slowly aromatic ketones give no reaction. 

The ej. can perform yet other reactions such as dechlorination of chlorinated aliphatic hydrocarbons. This can be either oxidative, in which case the products are ketones, or reductive, as with carbon tetrachloride which produces the highly toxic free radical CH2 (Salmon, Jones and Mackrodt, 1981). Moreover, the ej. carry at least two reducing enzymes a nitro-reductase and an azo-reductase, both of which produce primary amines. 

Surface modifications of polymers is brought about by the introduction of alcohol functionality, e.g., poly(tetrafluoroethylene-co-hexafluoropropylene) on reduction with sodium naphthalide in THF results in an unsaturated modified surface layer, the thickness of which is controlled with reaction time and temperature. The air sensitive surface contains alcohols, ketones, aliphatic C-H bonds in addition to C=C and C C. The more alcoholic groups are introduced by hydroboration-oxidation, but the esterification leads to the formation of ester in lower yield. This reveals that the reactivity of OH group is similar to hindered alcohols. The reactivity of the surface can be enhanced by chain extension of secondary surface alcohols with ethylene oxide to form a surface containing primary alcohols groups separated from the polymer backbone by C-2 spacer. On the other hand, primary alcohols are directly introduced to the surface by reaction of the reduced layer with 9-BBN, followed by carbonylation and reduction [5]. 

The reagent NB-Enantride is highly efficient in case of reduction of straight-chain aliphatic ketones. The reduction of 2-octanone with 79% ee is the highest achieved by any chemical reducing agent, thus far. 

The original synthesis discovered by Leuckart was the reductive alkylation of benzaldehyde to form benzylamine using formamide or ammonium formate as the reducing agent. This was later extended by Wallach and by the Eschweiler-Glarke procedure . The scope of the Leuckart reaction has been reviewed by Moore Apart from the special case of formaldehyde, the reaction is most focile with aromatic aldehydes and water-insoluble ketones. Aliphatic... 

Ketones aliphatic undiluted 15-25 2 Not resistant after a short time, the material is seriously affected (considerable reduction of the mechanical strength and changes in weight) using the material under these conditions is not recommended PVDF 1000 Quadrant EPP... 

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

Aliphatic hydrocarbons can be prepared by the reduction of the readily accessible ketones with amalgamated zinc and concentrated hydrochloric acid (Clemmensen method of reduction). This procedure is particularly valuable for the prep>aration of hydrocarbons wdth an odd number of carbon atoms where the Wurtz reaction cannot be applied with the higher hydrocarbons some secondary alcohol is produced, which must be removed by repeated distillation from sodium. 

Stability toward reduction makes hydrogen fluoride a good medium for different hydrogenation processes [1, 2] It is a useful solvent for the hydrogenation of benzene in the presence of Lewis acids [f ] Anhydrous hydrofluonc acid has pronounced catalytic effect on the hydrogenations of various aromatic compounds, aliphatic ketones, acids, esters, and anhydrides in the presence of platinum dioxide [2] (equations 1-3)... 

Aldehydes and ketones are similar in their response to hydrogenation catalysis, and an ordering of catalyst activities usually applies to both functions. But the difference between aliphatic and aromatic carbonyls is marked, and preferred catalysts differ. In hydrogenation of aliphatic carbonyls, hydrogenolysis seldom occurs, unless special structural features are present, but with aryl carbonyls either reduction to the alcohol or loss of the hydroxy group can be achieved at will. 

Plaiinum was more efficient lhan rhodium in ihese experimenis. These catalysts give excellent yields of tertiary amines in reductive alkylation of aliphatic secondary amines with ketones ( 6). 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

Recently, XAD was used as material to control the stereochemical course of microbial reductions [19], In the presence of XAD, simple aliphatic and aromatic ketones were reduced to the corresponding (S)-alcohols in excellent enantioselec-tivity while low enantioselectivities were observed in the absence of the polymer (Figure 8.23). 

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