2- Pentanone reduction

Reduction. Most ketones are readily reduced to the corresponding secondary alcohol by a variety of hydrogenation processes. The most commonly used catalysts are palladium, platinum, and nickel For example, 4-methyl-2-pentanol (methyl isobutyl carbinol) is commercially produced by the catalytic reduction of 4-methyl-2-pentanone (methyl isobutyl ketone) over nickel. 

Metalation ofa-sulfinyl dimethylhydrazones with terf-butylmagnesium bromide, butyllithium or lithium diisopropylamide, and reaction of the generated azaenolates with aldehydes, provides aldol adducts (e.g., 6) as mixtures of diastereomers. Reductive desulfurization leads to fi-hydroxy dimethylhydrazones (e.g., 7) which are cleaved to the desired /(-hydroxy ketones in 25% overall yield10 u. The enantiomeric excesses are about 50%, except for (- )-3-hydroxy-4-methyl-1-phenyl-1-pentanone (8) which was obtained in 88% ee. 

Since the transition state for alcohol oxidation and ketone reduction must be identical, the product distribution (under kinetic control) for reducing 2-butanone and 2-pentanone is also predictable. Thus, one would expect to isolate (R)-2-butanol if the temperature of the reaction was above 26 °C. On the contrary, if the temperature is less than 26 °C, (S)-2-butanol should result in fact, the reduction of... 

In the reduction of benzoyloxypropanone, the hydrophobic polymer XAD-7 was used to prevent product inhibition and increase substrate concentration [19b]. Thus, the reduction proceeded in 70 gl substrate concentration and afforded 87% (12.4 g) of (S)-l-benzoyloxy-2-propanol in >99% ee (Figure 8.24). Thebutanone derivative could be reduced with the same method and afforded (S)-alcohol in 72% yield and >99% ee, but the pentanone derivative could not be reduced. 

The reduction of nitro ketones with baker s yeast is a good method for the preparation of chiral nitro alcohols.89 The reduction of 5-nitro-2-pentanone with baker s yeast gives the corresponding (5)-alcohol, which is an important chiral building block. Various chiral natural products are prepared from it. In Scheme 7.16, the synthesis of the pheromone of Andrena haemorrhoa is described, where the acylation of the chiral nitro alcohol followed by radical denitration is involved as key steps.89a... 

Redox [Reduction oxidation] A process for separating the components of used nuclear fuel by solvent extraction. It was the first process to be used and was brought into operation at Hanford, United States, in 1951, but was superseded in 1954 by the Purex process. The key to the process was the alternate reduction and oxidation of the plutonium, hence the name. The solvent was Hexone (4-methyl-2-pentanone, methyl isobutyl ketone), so the process was also known as the Hexone process. The aqueous phase contained a high... 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

Figure 9.3 Enzyme-catalysed stereoselective reduction of 3-allyl-2,4-pentanedione 9.3.1 Procedure 1 Synthesis of (3/ ,4S)-3-Allyl-4-hydroxy-2-pentanone...

The reduction of ketones containing nitro groups to nitro alcohols is best carried out by borohydrides. 5-Nitro-2-pentanone was converted to 5-nitro-2-pentanol in 86.6% yield by reduction with sodium borohydride at 20-25°. Other nitro ketones gave 48.5-98.7% yields, usually higher than were obtained by Meerwein-Ponruiorf reduction [907]. 2-Acetamido-3-(p-nitrophenyl)-l-hydroxypropan-3-one was reduced with calcium borohydride at — 30° to 70% of threo- and 10% of er7tAro-2-acetamido-3-(p-nitrophenyl)propane-l,3-diol while sodium borohydride afforded a mixture of the above isomers in 25% and 47% yields, respectively [902]. 

Pentadienone (divinyl ketone) was epoxidized55 by means of hydrogen peroxide in alkaline solution, to give a mixture of DL- and me.so-l,2 4,5-dianhydro-3-pentanones in the ratio of 13 7. Reduction of the ketone group in the DL-diepoxide with sodium horohvdride, followed by alkaline hydrolysis in dimethyl sulfoxide, was fully stereo-specific, and afforded DL-arabinitol. The same reaction-sequence performed on the meso-diepoxide led to a mixture of ribitol and xylitol. 

Aldol reactions.1 The chiral oxazolidine (1), formed from 3-pentanone and (-)-norephedrine, after conversion to the tin azaenolate reacts with aldehydes to give predominantly anti-aldols (2) in >90% ee. Reduction of the carbonyl group of the anti-aldol 2 provides (3S,4R)-4-methyl-3-heptanol (3) in 95% ee. 

Even when the reductive processes, so evident in metal-stimulated processes, are avoided, several side reactions can still cause reductions in the yield of the desired a-arylated ketones. The first, abstraction of 3-hydrogen atoms from the enolate ion by the aryl radical, has already been mentioned (Section 2.2.2.1) and is sometimes a serious, chain-terminating process.43 5 This abstraction reaction, however, appears to be quite unpredictable. 3-Hydrogen abstraction from the enolate of 2,4-dimethyl-3-pentanone (PriCOPr Table 1) which severely disrupts the reaction with iodobenzene, does not prevent high-yielding reactions of the same enolate (and those from other ketones with a-branching) with many other substrates. In in-... 

Figure 5.16 Enantioselectivity of the redox reaction of ADH from T. ethanolicus with different alcohols (Pham, 1990). Temperature dependence of free energy of activation differences for 2-butanol and 2-pentanol open squares 2-butanol open circles 2-pentanol filled square reduction of 2-butanone filled circle reduction of 2-pentanone.

The NADP-dependent TBADH was used for the laboratory-scale preparation of several chiral aliphatic and cyclic hydroxy compounds by reduction of the corresponding ketones. For the regeneration of NADPH, this reduction reaction can be coupled with the TBADH catalyzed oxidation of isopropanol. For the reduction of some ketones it was observed that the reaction rate was increased in the presence of the regenerating substrate isopropanol, for instance in the presence of 0.2 v/v isopropanol, the reduction rate of butanone or pentanone was increased 3-4-fold [57], In some cases, the enantiomeric excess of the reduction reaction is not very high, especially when small molecules are converted, but also for compounds such as acetophenone [138]. 

The reductive dehalogenation predominates in the photoinduced reactions of 32 with 3-pentanone, 2-methyl-3-pentanone, and 2,4-dimethyl-3-pentanone. Although, substitution is favored over reduction in all of the reactions of 32 with cyclic ketone enolates, a competing reduction is responsible for the lower yields observed with cyclopentanone and cyclohexanone compared to cyclooctanone (Scheme 10.59) [73]. 

Dihaloketones. A number of studies of the electroreduction of a,a -dibromoketones have been reportedly directed to obtaining evidence for the the intermediacy of cyclo-propanone-derived intermediates (186). Reduction of 2,4-dibromo-2,4-dimethyl-3-pentanone (185) consumed two Faradays of current and gave a species which is briefly stable at -32 °C. The intermediate (186) could be intercepted by subsequent addition of a protonic trapping agent to the low-temperature catholyte (equation 100). Results have... 

The yields of primary amines over platinum oxide were improved in the presence of an excess molar equivalent of ammonium chloride in low pressure reductive alkylation of ammonia with ketones in methanol saturated with ammonia.10 With acetophenone and 4-methyl-2-pentanone, the yields of primary amine increased from 37 and 49% in the absence of ammonium chloride to 69 and 57-65%, respectively, in the presence of ammonium chloride. Moller obtained a much higher yield (>90%) of 1-phenethylamine from acetophenone by adding a small amount of acetic acid to methanol-ammonia with Raney Ni (eq. 6.6).15 The reductive amination of benzophenone in the presence of Raney Co and some ammonium acetate gave 70% yield ofbenzohy-drylamine, compared to only 19% under usual conditions with Raney Ni.3... 

Mylroie et al. studied the optimal conditions for reductive alkylation of A-(4-ni-trophenyl)acetamide with ketones using Pt-C and sulfided Pt-C.49 In general, the sulfided catalyst was superior in the yield of the alkylated amines. There was no indication of either reduction of the ketone or saturation of the ring. With a higher loading of ketone (6 equiv) at 100°C and 6.9 MPa H2 in ethanol, excellent yields (98.5-99%) of the alkylated amines were obtained from the reaction of acetone (eq. 6.24), cyclohexanone, 2-pentanone, and 3-pentanone with A-(4-ni-trophenyl)acetamide. 

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