Ketone important

Figure 1-17-3 presents a diagram of pathways in which selected amino acids are converted to citric add cyde intermediates (and glucose) or to acetyl CoA (and ketones). Important genetic defidendes are identified on the diagram. 

Another process mechanistically related to imine exchange is the dynamic production of pyrazolotriazinones reported in 2005 by Wipf and coworkers [29]. After first verifying that reaction of either 16 or 17 with equimolar quantifies of isobutyraldehyde and hydrocinnamaldehyde at 40°C in water (pH 4.0) resulted in the same 3 7 mixture of 16 and 17 at equilibrium (Fig. 1.6, Eq. 1), the authors demonstrated that a library could be generated by reaction of pyrazolotriazinone 16 with a series of aldehydes (Fig. 1.6, Eq. 2). Direct metathesis of pyrazolotriazinones was also demonstrated, as was reaction with ketones. Importantly, equilibration was halted by raising the pH to 7. 

Major markets as solvents and intermediates have made the ketones important commercial products lor many years. Acetone and mcthylethyl ketone have had the most impact on the chemical industry Acetone Is used s an intermediate In methyl isobutyl ketone, methyl methacrylate, diucelonc alcohol. ketone. hisphenol-A. phiwnc. and mesityl oxide Acetone is largely produced by dehydration of isopropyl alcohol In the production of phenol from cumene, acetone is produced as a by-product This mute to acetone has tended to control its price. 

Base-catalyzed rearrangement of o-acyloxyke-tones to (i-di ketones, important intermediates in the synthesis of chromones and flavones. 

Cerium enolates also provide favorable routes to a-bromo-/8-hydroxy ketones, important intermediates to a,/8-epoxy ketones. 

An interesting extension of this method involves the reaction of Af-silyl oxyketene imines derived from cyanohydrins (Scheme 19) [81]. By judicious selection of the protecting group on the oxygen, highly functionalized (3-hydroxy cyanohydrins can be accessed with high levels of enantio- and diastereoselectivity. These products can then be transformed into a diversity of structural motifs (amines, aldehydes, imines, ketones) important for the synthesis of polyketide and other classes of natural products. In addition, the ethers can be easily converted to enantiomerically enriched unsymmetrical benzoins, thus revealing the synthetic equivalency of A-silyl oxyketene imines as acyl anions (Scheme 19). 

With dilute sulphuric acid citral forms p-cymene. Citral can be condensed with propa-none to form a ketone, pseudoionone, C13H20O, which is technically important, as it is readily convertible into a and -ionone. 

The properties of the solids most commonly encountered are tabulated. An important problem arises for petroleum fractions because data for the freezing point and enthalpy of fusion are very scarce. The MEK (methyl ethyl ketone) process utilizes the solvent s property that increases the partial fugacity of the paraffins in the liquid phase and thus favors their crystallization. The calculations for crystallization are sensitive and it is usually necessary to revert to experimental measurement. 

Hydrazine and its alkylated derivatives are used as rocket fuels in organic chemistry, substituted phenylhydrazines are important in the characterisation of sugars and other compounds, for example aldehydes and ketones containing the carbonyl group C=0. 

Dinitrophenylhydrazine is a very important reagent for the identification of aldehydes and ketones (pp. 342, 346). It is readily prepared from chloro-2,4-dinitrobenzene (I). In the latter compound the chlorine is very reactive in... 

It follows therefore that ethyl malonate can be used (just as ethyl aceto- acetate) to prepare any mono or di-substituted acetic acid the limitations are identical, namely the substituents must necessarily be alkyl groups (or aryl-alkyl groups such as CjHjCHj), and tri-substituted acetic acids cannot be prepared. Ethyl malonate undergoes no reaction equivalent to the ketonic hydrolysis of ethyl acetoacetate, and the concentration of the alkali used for the hydrolysis is therefore not important. 

Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

An important general method of preparing indoles, known as the Fischer Indole synthesis, consists in heating the phenylhydrazone of an aldehyde, ketone or keto-acld in the presence of a catalyst such as zinc chloride, hydrochloric acid or glacial acetic acid. Thus acrtophenone phenylhydrazone (I) gives 2-phenyllndole (I V). The synthesis involves an intramolecular condensation with the elimination of ammonia. The following is a plausible mechanism of the reaction ... 

The production of both an alcohol and the sodium salt of an acid might easily be confused with the hydrolysis products of an ester (in the above instance benzyl benzoate). Such an error would soon be discovered (e.g., by reference to the b.p. and other physical properties), but it would lead to an unnecessary expenditure of time and energy. The above example, however, emphasises the importance of conducting the class reactions of neutral oxygen-containing compounds in the proper order, viz., (1) aldehydes and ketones, (2) esters and anhydrides, (3) alcohols, and (4) ethers. 

Lithium l,3-dithian-2-ides (p. 6, 8) may be alkylated with alkyl bromides or iodides. Steric hindrance is usually of little importance and the resulting ketone can be easily liberated by hydrolysis (D. Seebach, 1969). 

Torgov introduced an important variation of the Michael addition allylic alcohols are used as vinylogous a -synthons and 1,3-dioxo compounds as d -reagents (S.N. Ananchenko, 1962, 1963 H. Smith, 1964 C. Rufer) 1967). Mild reaction conditions have been successful in the addition of ],3-dioxo compounds to vinyl ketones. Potassium fluoride can act as weakly basic, non-nudeophilic catalyst in such Michael additions under essentially non-acidic and non-basic conditions (Y. Kitabara, 1964). 

Low-valent nitrogen and phosphorus compounds are used to remove hetero atoms from organic compounds. Important examples are the Wolff-Kishner type reduction of ketones to hydrocarbons (R.L. Augustine, 1968 D. Todd, 1948 R.O. Hutchins, 1973B) and Barton s olefin synthesis (p. 35) both using hydrazine derivatives. 

No intennolecular reaction of malonate or /3-keto esters with halides has been reported, but the intramolecular reaction of /3-diketones such as 790 and malonates proceeds smoothly[652,653]. Even the simple ketone 791 can be arylated or alkenylated intramolecularly. In this reaction, slow addition of a base is important to prevent alkyne formation from the vinyl iodide by elim-ination[654]. 

Acetoxy-l,7-octadiene (40) is converted into l,7-octadien-3-one (124) by hydrolysis and oxidation. The most useful application of this enone 124 is bisannulation to form two fused six-membered ketonesfl 13], The Michael addition of 2-methyl-1,3-cyclopentanedione (125) to 124 and asymmetric aldol condensation using (5)-phenylalanine afford the optically active diketone 126. The terminal alkene is oxidi2ed with PdCl2-CuCl2-02 to give the methyl ketone 127 in 77% yield. Finally, reduction of the double bond and aldol condensation produce the important intermediate 128 of steroid synthesis in optically pure form[114]. 

By analogy to the hydration of alkenes hydration of an alkyne is expected to yield an alcohol The kind of alcohol however would be of a special kind one m which the hydroxyl group is a substituent on a carbon-carbon double bond This type of alcohol IS called an enol (the double bond suffix ene plus the alcohol suffix ol) An important property of enols is their rapid isomerization to aldehydes or ketones under the condi tions of their formation... 

The next several chapters deal with the chemistry of various oxygen containing func tional groups The interplay of these important classes of compounds—alcohols ethers aldehydes ketones carboxylic acids and derivatives of carboxylic acids— IS fundamental to organic chemistry and biochemistry... 

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

The carbonyl carbon of a ketone bears two electron releasing alkyl groups an aldehyde carbonyl group has only one Just as a disubstituted double bond m an alkene is more stable than a monosubstituted double bond a ketone carbonyl is more stable than an aldehyde carbonyl We 11 see later m this chapter that structural effects on the relative stability of carbonyl groups m aldehydes and ketones are an important factor m then rel ative reactivity... 

To the synthetic chemist the most important of the reactions m Table 17 1 are the last two the oxidation of primary alcohols to aldehydes and secondary alcohols to ketones Indeed when combined with reactions that yield alcohols the oxidation methods are so versatile that it will not be necessary to introduce any new methods for preparing aide hydes and ketones in this chapter A few examples will illustrate this point... 

Many low molecular weight aldehydes and ketones are important industrial chem icals Formaldehyde a starting material for a number of plastics is prepared by oxida tion of methanol over a silver or iron oxide/molybdenum oxide catalyst at elevated temperature... 

The chemistry of the carbonyl group is probably the single most important aspect of organic chemical reactivity Classes of compounds that contain the carbonyl group include many derived from carboxylic acids (acyl chlorides acid anhydrides esters and amides) as well as the two related classes discussed m this chapter aldehydes and ketones... 

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