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Enol esters alkyl

Low molecular mass enol esters (e.g. acetates H.O. House, 1965) or enol ethers (e.g. silyl ethers H.O. House, 1969) of ketones can be synthesized regioselectively and/or separated by distillation. Treatment with lithium alkyls converts them into the corresponding lithi-... [Pg.57]

In their original communication on the alkylation and acylation of enamines, Stork et al. (3) had reported that the pyrrolidine enamine of cyclohexanone underwent monoacylation with acid chlorides. For example, the acylation with benzoyl chloride led to monobenzoylcyclohexanone. However, Hunig and Lendle (33) found that treatment of the morpholine enamine of cyclopentanone with 2 moles of propionyl chloride followed by acid hydrolysis gave the enol ester (56), which was proposed to have arisen from the intermediate (55). [Pg.20]

Thus the reactions of cyclic or acyclic enamines with acrylic esters or acrylonitrile can be directed to the exclusive formation of monoalkylated ketones (3,294-301). The corresponding enolate anion alkylations lead preferentially to di- or higher-alkylation products. However, by proper choice of reaction conditions, enamines can also be used for the preferential formation of higher alkylation products, if these are desired. Such reactions are valuable in the a substitution of aldehydes, which undergo self-condensation in base-catalyzed reactions (117,118). Monoalkylation products are favored in nonhydroxylic solvents such as benzene or dioxane, whereas dialkylation products can be obtained in hydroxylic solvents such as methanol. The difference in products can be ascribed to the differing fates of an initially formed zwitterionic intermediate. Collapse to a cyclobutane takes place in a nonprotonic solvent, whereas protonation on the newly introduced substitutent and deprotonation of the imonium salt, in alcohol, leads to a new enamine available for further substitution. [Pg.359]

Due to the nonaromatic character of the oxepin system the oxepinones do not usually form stable enol structures. By O-acylation or O-alkylation, however, the enol forms can be stabilized as enol esters and ethers, respectively. A large number of substituted 1-benzoxepins have been synthesized by this route. Acetylation of l-benzoxepin-3(2//)-ones 1 and l-benzoxepin-5(2/T)-ones 3 was readily achieved with acetic anhydride in the presence of an appropriate base such as pyridine, triethylamine or sodium acetate.t5,t6 t72 176... [Pg.24]

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... [Pg.482]

Therefore, transesterification reactions frequently fail when R is tertiary, since this type of substrate most often reacts by alkyl-oxygen cleavage. In such cases, the reaction is of the Williamson type with OCOR as the leaving group (see 10-14). With enol esters, the free alcohol is the enol of a ketone, so such esters easily... [Pg.487]

Among the compounds capable of forming enolates, the alkylation of ketones has been most widely studied and applied synthetically. Similar reactions of esters, amides, and nitriles have also been developed. Alkylation of aldehyde enolates is not very common. One reason is that aldehydes are rapidly converted to aldol addition products by base. (See Chapter 2 for a discussion of this reaction.) Only when the enolate can be rapidly and quantitatively formed is aldol formation avoided. Success has been reported using potassium amide in liquid ammonia67 and potassium hydride in tetrahydrofuran.68 Alkylation via enamines or enamine anions provides a more general method for alkylation of aldehydes. These reactions are discussed in Section 1.3. [Pg.31]

Nitroethylene is extremely reactive and sensitive to strong basic conditions, but various ketone and ester enolates undergo alkylation with nitroethylene at low temperature (Eq. 4.5165 and Table 4.1). [Pg.87]

Silyl enol ethers, enol esters and alkyl enol ethers of ketones and aldehydes can be C-alkylated with reactive alkylating agents in the presence of Lewis acids86-90. However, information regarding the use of these reactions for diastereoselcctive or asymmetric synthesis is still limited. [Pg.719]

It is important to note that a possible photochemical ring expansion by [1,3]- or [l,5]-acyl shifts in the 5-membered vinyl lactams 191 has not been observed,4,116 nor have [l,5]-shifts of acyl groups involving an aromatic ring been reported for either enol esters or enamides. However, an example of a similar [l,5]-alkyl shift, 193 -> 194, in related ketene dialkyl acetals is known.24... [Pg.155]

Hydrolysis of enol esters 0-83 Reduction of acyl halides 0-84 Reduction of carboxylic acids, esters, or anhydrides 0-85 Reduction of amides 0-95 Alkylation and hydrolysis of imines, alkylation of aldehydes 0-97 Alkylation and hydrolysis of dithi-anes... [Pg.1270]

Coupling with enol esters (7, 93). A new synthesis of an alkyl-substituted alkene involves coupling of a lithium dialkyl cuprate with an enol triflate,1 available from a ketone by reaction with triflic anhydride and 2,6-di-t-butylpyridine.2 A wide variety of organocuprates can be used and the geometry of the enolate is largely retained. Reported yields are in the range 60 100%. [Pg.282]

Enoate 3-substitution and 3-disubstitution cause a decrease in the rate of the initial conjugate addition step of the reaction sequence that is directly related to the steric bulk of the substituent.103,105 Equation (24) provides a representative case in the a-alkylation of enoates by means of conjugate amination-enol-ate alkylation followed by dehydroamination.106 When 3-substitution results in stereoisomeric ( )- and (Z)-alkenoate substrates, tandem difunctionalization typically proceeds with greater facility for ( )-isomers.64103 Obviously, when the double bond of the ester is part of a medium-sized ring, an ( )-alke-noate geometry is mandated in such cases, tandem vicinal difunctionalization proceeds with uniformly excellent results (equation 25).25... [Pg.247]

Ester-substituted ketone enolates are stabilized, and these enolates can be alkylated (ace-toacetic ester synthesis). Alkylation is, however, also possible for enolates that are not stabilized. In the case of the stabilized enolates, the alkylated ketones are formed in two or three steps, while the nonstabilized enolates afford the alkylated ketones in one step. However, the preparation of nonstabilized ketone enolates requires more aggressive reagents than the ones employed in the acetoacetic ester synthesis. [Pg.546]

The situation changes when chiral ester enolates or chiral amide enolates are alkylated. There, the half-spaces on the two sides of the enolate planes of the substrates are diastereotopic, and alkylating reagents can react from one of the sides selectively (see discussion in Section 3.4.1). Stereogenic alkylations of such enolates therefore may take place diastereo selectively. [Pg.554]

Why are the benzylated esters of Figure 10.37 not obtained with higher diastereose-lectivities than 95 or 97%, respectively One of the reasons, and perhaps the only reason, lies in the failure of both the E - and the Z"-enolate to form with perfect stereocontrol. Small contaminations of these enolates by just 5 or 3% of the corresponding enolate with the opposite configuration would explain the observed amounts of the minor diastereoisomers, even if every enolate were alkylated with 100% diastereoselectivity. [Pg.404]


See other pages where Enol esters alkyl is mentioned: [Pg.191]    [Pg.291]    [Pg.265]    [Pg.187]    [Pg.77]    [Pg.817]    [Pg.1018]    [Pg.280]    [Pg.58]    [Pg.26]    [Pg.70]    [Pg.593]    [Pg.191]    [Pg.100]    [Pg.101]    [Pg.50]    [Pg.498]    [Pg.102]    [Pg.97]    [Pg.15]    [Pg.557]    [Pg.351]    [Pg.732]   


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Alkyl esters

Alkylations ester enolates

Enol alkyl

Enol esters

Enolate alkylation

Enolates alkylation

Enolates enol esters

Enols alkylation

Ester enolate

Ester enolate alkylation

Esters alkylation

Esters enolates

Esters enolization

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