Ketone molecules additions

Although the conversion of an aldehyde or a ketone to its enol tautomer is not generally a preparative procedure, the reactions do have their preparative aspects. If a full mole of base per mole of ketone is used, the enolate ion (10) is formed and can be isolated (see, e.g., 10-105). When enol ethers or esters are hydrolyzed, the enols initially formed immediately tautomerize to the aldehydes or ketones. In addition, the overall processes (forward plus reverse reactions) are often used for equilibration purposes. When an optically active compound in which the chirality is due to an asymmetric carbon a to a carbonyl group (as in 11) is treated with acid or base, racemization results. If there is another asymmetric center in the molecule. 

Example More extensive substitution at the oxirane system brings additional dissociation pathways for the molecular ions. Nevertheless, one of the main reaction paths of molecular ions of glycidols gives rise to enol radical ions by loss of a aldehyde (R = H) or ketone molecule. [218] The reaction mechanism can be rationalized by the assumption of a distonic intermediate (Scheme 6.78) ... 

It turns out that a reaction still occurs because the carbonyl group itself is an electrophile. As the enolate forms, it can attack the carbonyl group of another aldehyde or ketone molecule. This is an aldol reaction or aldol condensation, also called an aldol addition. 

The quantum yield for this process at 3130 A. has been determined to be of the same order of magnitude in the vapor phase, in the pure liquid and in methyl pentane solution (29). The significance of this surprising result is difficult to assess at present since the data are sparse. In photolysis in aqueous solution a reaction has been observed (17) which bears resemblance to both eq. 18 and 52. It leads to the formation of caproic acid, the net reaction being the addition of a molecule of water and cleavage of the ring in the ketone molecule. 

The addition of the second ketone molecule (path b) is promoted by the fact that the formation of a double bond from intermediate 152 is unfavored when R2 = H98. 

To sum up, nucleophilic substitution at an olefinic carbon (at any rate, at the sharply electrophilic one, as in 3-substituted vinyl aryl ketones) involves addition of a nucleophile followed by formation of the PhC(0)CHCHXY anion, whose fate depends on the rate at w hich the group X leaves the molecule. If X leaves the molecule as soon as Y" attacks,... 

In addition to the products mentioned hitherto, the formation of various condensed products was also reported in the liquid phase and in solu-tion in addition, the formation of cyclohexanone pinacoP and caproic acid in cyclohexanol and water solutions, respectively, was observed. Moreover, aliphatic alcohols with carbon atom numbers equal to those of the original ketones were found in the liquid phase and also in solution It is probable that these products were formed by the interaction between the excited and the normal ketone molecules or in the reaction of the excited ketone with the solvent. These processes may be symbolized as... 

The chemoselectivity of organo-titanium and -zirconium reagents is practically unaffected by the nature of the nucleophilic moiety of their molecule. Although aldehydes always react much faster than ketones, the addition rates sometimes differ significantly, depending upon steric and electronic properties... 

The reactions are usually carried out by adding the halo ketone to a solution or suspension of the base in either a protic solvent (water, alcohols) or an ether (diethyl ether, dioxane, dimethoxyethane). The bases employed include hydroxides of Group I and Group II metals alkoxides, carbonates and hydrogen-carbonates of Group I metals ammonia, and amines. There is no one recommended set of experimental conditions, because both the mechanism of the reactions and the type of products obtained depend upon the initial choice of a-halo ketones. In addition, since the halo ketones are highly reactive molecules, side products are inevitably obtained those most commonly produced are shown in Scheme... 

Insight into the photochemical reactions between deoxycholic or apocholic acid ( choleic acids ) and guest molecules in crystalline inclusion complexes has been obtained by X-rzy studies. The choleic acids form channels with wall structures determined by the nature of the guest molecule. Guest ketones of various types react photochemically by addition to the choleic acid at a site determined by the orientation of the ketone molecule in relation to the host (e.g. deoxycholic acid reacts at C-5 or C-6 with linear aliphatic ketones, but at C-16 with cyclohexanone).12... 

The yields of the pyrimidines 147 and the pyridines 151 are not high and vary greatly, depending on the structure of the starting materials. The latter can also determine the nature of the product. Thus, a mixture of 2,4-dimethyl-6-phenylpyrimidine, 2,4-dimethyl-4,6-diphenyl-4//-l,3-oxazine and 1-chloro-l-phenylethene was obtained by refluxing a 1 3 3 ratio of the acetophenone-benzonitrile-phosphorus oxychloride mixture, followed by treatment of the crude product with sodium carbonate solution .It has been shown that addition of an additional ketone molecule to the iminium intermediate is an alternative to the formation of the A -acylenamines and this route is catalyzed by aluminum chloride. Auricchio and coworkers believe also that the reaction of ketones with nitriles catalyzed with both protic and Lewis acids must be considered as a Ritter reaction (see, however, Section V.C). The cationic intermediate 152 thus formed can undergo either a proton shift giving enamide 153 or addition of another ketone molecule... 

An aldol addition is a reaction between two molecules of an aldehyde or two molecules of a ketone. When the reactant is an aldehyde, the addition product is a jS-hydroxyaldehyde, which is why the reaction is called an aldol addition ( aid for aldehyde, ol for alcohol). When the reactant is a ketone, the addition product is a jS-hydroxyketone. Because the addition reaction is reversible, good yields of the addition product are obtained only if it is removed from the solution as it is formed. 

The tolerance to polar groups was tested in this system by running ethylene polymerizations in the presence of small molecule additives at a level of approximately 1500 equiv per metal center. On the basis of decreases in both molecular weight and catalyst turn over numbers, the neutral nickel catalysts displayed decreasing tolerance to functional groups in the following order ethers > ketones > esters > water > alcohols > tertiary amines. 

Purpose. We prepare the first of three intermediates on the synthetic pathway to our target molecule, a photochromic imine. A base-catalyzed aldol reaction is carried out in which an aromatic aldehyde is condensed with an aryl alkyl ketone. This addition reaction is followed by dehydration to form an a,p-unsaturated ketone this particular product is commonly called a chalcone. This intermediate is isolated and purified for use as the starting material in the next stage of the synthesis. You will carry out a semimicroscale reaction to gain experience at conducting larger-scale organic reactions. 

The mechanism of the base-catalyzed aldol reactions involves initial deprotonation of the a-hydrogen in base to create an enolate anion, which is a strong nucleophile that attacks another aldehyde or ketone molecule to give a carbonyl addition intermediate, which, in turn, reacts with water to create a j8-hydroxy aldehyde or ketone product and regenerates the original base. 

The second and third steps in Fischer esterification are also completely analogous to parts of aldehyde or ketone chemistry. A molecule of alcohol acts as a nucleophile and adds to the carbonyl carbon of the protonated carbonyl group (Fig. 17.21). For a ketone, this addition is followed by deprotonation, and gives the hemiacetal for the acid, a somewhat more complicated intermediate with one more hydroxyl group is formed. In both reactions, however, a planar, hybridized carbon has been converted into an intermediate with a tetrahedral carbon, called the tetrahedral intermediate. 

Without additional reagents 1,1 Hydroxyhalides from ketones Hemiketals from 2 ketone molecules... 

Without additional reagents A Mmidazoline-5-thiones from 2 methyl ketone molecules... 

The authors found that tert-benzylalcohols undergo selective dehydroarylation through P-carbon elimination with the liberation of a ketone molecule in the presence of Pd(OAc)2 in combination with a bulky phosphine such as P(l-naphthyl)3. For example, 2-(l-naphthyl)-2-propanol or (l-naphthyl)diphenylmethanol gives naphthalene along with the corresponding ketone under the catalytic conditions (Scheme 4.95) [93]. Addition of a catalytic amount of bromobenzene together with a base enhances the product yield. This may be attributed to the... 

Grignard synthesis with self-condensation 1,3-Diols from 2 ketone molecules Inverse addition... 

Iron(III) chloride forms numerous addition compounds, especially with organic molecules which contain donor atoms, for example ethers, alcohols, aldehydes, ketones and amines. Anhydrous iron(III) chloride is soluble in, for example, ether, and can be extracted into this solvent from water the extraction is more effective in presence of chloride ion. Of other iron(III) halides, iron(III) bromide and iron(III) iodide decompose rather readily into the +2 halide and halogen. 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

A number of compounds of the general type H2NZ react with aldehydes and ketones m a manner analogous to that of primary amines The carbonyl group (C=0) IS converted to C=NZ and a molecule of water is formed Table 17 4 presents exam pies of some of these reactions The mechanism by which each proceeds is similar to the nucleophilic addition-elimination mechanism described for the reaction of primary amines with aldehydes and ketones... 

Hemiacetal (Section 17 8) Product of nucleophilic addition of one molecule of an alcohol to an aldehyde or a ketone Hemiacetals are compounds of the type... 

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