Ketones 4-hydroxy-4-methyl-2-pentanone

Hydroxy-2-butanone and its methyl ether were also hydrogenated in 69 and 68% ee, respectively, using the same modified nickel catalyst.211 Acetylacetone was first hydrogenated to (R)-4-hydroxy-2-pentanone in 87% ee over the Raney Ni modified by (R,R)-tartaric acid. Then the (R)-hydroxy ketone was hydrogenated to a mixture of... 

Methyl-4-hydroxy-2-pentanone (diacetone alcohol) could be used as nucleophile instead of acetone (3a) [15], giving the expected aldol products 4 (R =H) with lower enantioselectivities (48-86% ee). A tandem organo- and biocatalytic process has been designed [16], with the aim of improving the achieved enantioselectivities for the a-hydroxy ketones 4 (R =H), using Pseudomonas cepacia lipase (Amano 1) as catalyst for the kinetic resolution of the mixture of aldol adducts obtained after the proline-catalyzed reaction. 

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. 

The procedure reported here provides a convenient method for the a-hydroxylation of ketones which form enolates under the reaction conditions. The reaction has been applied successfully to a series of para-substituted acetophenones, 1-phenyl-1-propanone, 3-pentanone, cyclopentanone, cyclohexanone, cycloheptanone, cyclododecanone, 2-methyl cyclohexanone, 2-norbornanone and benzalacetone. In the case of a steroidal example it was shown that a carbon-carbon double bond and a secondary hydroxyl group are not oxidized. A primary amino function, as in the case of p-aminoacetophenone, is not affected.5 Similarly, a tertiary amino ketone such as tropinone undergoes the a-hydroxy at ion reaction.5... 

The alicyclic ketones have been identified as being important flavor precursors by Flament et al. (15) and more recently by MacLeod and Ames (44), who identified a similar compound (3-methyl-cyclo-pentanone) in heated ground beef. Flament et al. (15) singled out the importance of these compounds, particularly in the presence of alhylpyrazines. Nishimura et al. (41) produced a meaty odor by heating 2-hydroxy-3-methylcyclopent-2-enone with cyclotene and HaS. Two volatile compounds described as having meaty odor were 2-methyl-cyclopentanone and 3-methylcyclopentanone. Thus, cyclotene appears to be a key precursor of "roast beef" flavor. 

Stereoselective aldol condensation. Heathcock and Buse have previously employed 2-methyl-2-trimethylsiloxy-3-pentanone (1) in a highly stereoselective route to 3-hydroxy-2-methylcarboxylic acids (8, 295). Aldol condensation of the lithium enolate derived from 1 with a chiral aldehyde yields ery//iro-aldols, which are cleaved with periodic acid to -hydroxy carboxylic acids. However, when 1 is condensed with a chiral aldehyde such as 2, two eryt/iro-products (3 and 4) are produced. Heathcock and co-workers now report that the 1,2-diastereoselectivity of these aldol condensations can be enhanced by use of the ketone 5. Reaction of racemic 5 with racemic aldehyde 2 furnishes a single (racemic) adduct 6. 

The results of Barltrop and Coyle , on the photolysis of aliphatic ketones in solution at 3130 A, support the explanation suggested by Wagner and Hammond for the low quantum yields. The overall quantum yield for disappearance of 2-pentanone, 2-octanone and 5-methyl 2-octanone was found to increase and approach unity in hydroxylic solvents. This increase can be attributed to the solvation of the hydroxy biradical intermediate. Since, however, the solvent effect was not observed for products originating from excited singlet molecules, it is probably only the triplet state which decomposes via biradicals. 

These cyclization reactions were also possible with or without a metal ion template using a,j3-unsaturated ketones, such as mesityl oxide or methyl vinyl ketone, or with /3-hydroxyketones, such as 4-hydroxy-4-methyl-2-pentanone. The products were the same as when simple carbonyl compounds were used showing that the reaction with the simple carbonyl compounds proceded... 

Hydrated lime is used as an alkaline catalyst to promote the self-condensation of acetone to form diacetone alcohol (4-hydroxy-4-methyl-2-pentanone) [31.26]. Diacetone alcohol is used as a solvent for natural and synthetic resins. It is also used as an intermediate in the produetion of mesityl oxide, methyl isobutyl ketone and hexylene glycol. 

Diacetone alcohol [123-42-2] (4-hydroxy-4-methyl-2-pentanone) is an almost odorless ketone alcohol that is weakly acidic as a result of rearrangement to the enol form. It is miscible with water and organic solvents except aliphatic hydrocarbons. It acts as a good solvent for cellulose esters and ethers, alcohol-soluble resins, castor oil, and plasticizers. Poly(vinyl acetate) and chlorinated rubber are partially dissolved or swollen. Polystyrene, poly(vinyl chloride), vinyl chloride copolymers, dam-ar resins, resin esters, rubber, bitumen, mineral oils, ketone resins, and maleate resins are insoluble. Diacetone alcohol is used as a high boiler in stoving enamels to improve flow and gloss. 

Thus, a short-range strategy for the synthesis of 4-hydroxy-l-phenyl-pentanone-2 (I) will lead to the two carbonyl compounds methyl benzyl ketone and acetaldehyde as synthesis precursors (Figure 1). Having reached this conclusion it is absolutely necessary to consider whether those two precursors will react by the anticipated aldol condensation to the target compound (I). A closer inspection based on insight into chemical reactivity has to decide that this reaction will not proceed unequivocally to the desired product (I). Rather, a mixture of compounds will be obtained including the... 

Synonyms DM Diacetone Diketone alcohol 4-Hydroxy-1-keto-4-methylpentane 4-Hydroxy-4-methyl-2-pentanone 4-Hydroxy-4-methylpentanone-2 4-Hydroxy-4-methyl pentan-2-one 2-Methyl-2-pentanol-4-one 2-Pentanone, 4-hydroxy-4-methyl-Classificatbn Ketone Em/mral CeHcOi Formu/a (CH3)2C(OH)CH COCH,... 

Pentanone Pentanone-3. See Diethyl ketone 2-Pentanone, 4-hydroxy-4-methyl-. See Diacetone alcohol 2-Pentanone, 4-methoxy-4-methyl-. See4-Methoxy-4-methylpentanone-2... 

Because the steps in an aldol addition mechanism are readily reversible, a tetro-aldol reaction can occur that converts a jS-hydroxy aldehyde or ketone back to the precursors of an aldol addition. For example, when 4-hydroxy-4-methyl-2-pentanone is heated with hydroxide in water, the final equilibrium mixture consists primarily of acetone, the retro-aldol product. 

Ketones can undergo the aldol reaction too, and the mechanism is similar to that for the aldol condensation of aldehydes. We will use acetone as an example (Fig. 19.72). In base, the enolate is formed first, and adds to the electrophilic carbonyl compoimd. Protonation by water yields a molecule once known as diacetone alcohol, 4-hydroxy-4-methyl-2-pentanone. 

In a pioneering investigation, the lithium enolate derived from 3-methyl-2-pentanone was added to aldehydes. Only moderate diastereoselectivity was obtained, however [119]. Exceptionally high induced stereoselectivity was observed when camphor-derived ketone 69 was converted into the lithium enolathe and subsequently added to aldehydes. a-Cleavage at the carbonyl group enabled the formation of y -hydroxy aldehydes and acids in high enantiomeric excess (Eq. (31)) [60]. The work on the aldol addition of methyl ketones led to a variety of stereoselective variants which rely mainly on boron enolates and will be discussed in Chapter 3 of Part I of this book. 

So far, we have discussed only aldehydes as substrates in the aldol condensation. What about ketones Treatment of acetone with base does indeed lead to some 4-hydroxy-4-methyl-2-pentanone, but the conversion is poor because of an unfavorable equilibrium with starting material. 

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