Ketones enolate anions

Scheme 8.40 BF3 Et20-promoted epoxide ring-opening by ketone enolate anion.

As an extension of the reaction of sulphinates with organometallic compounds, the Claisen-type condensation between ketone enolate anions 101 and arenesulphinates may be considered. It was found161,162 that this reaction provides an interesting synthetic approach to a-ketosulphoxides 102 (equation 54 Table 9). 

THF but a dimer in DME. X-ray crystallography of ketone enolate anions have shown that they can exist as tetramers and hexamers. There is also evidence that... 

Disubstitution products are obtained when dihalobenzenes (Cl, Br, I) react with aliphatic ketone enolate anions. Conversely, the reactions of o-iodohalobenzenes (X = I, Br, Cl) with the enolate anions of aromatic ketones, such as acetophenone, propiophenone and 2-naphthyl methyl ketone in DMSO yield mainly monosubstitution with the retention of one halogen (Scheme 10.7). The extent of dehalogenation is explained in terms of the energetics of the intramolecular ET from the ArCO-7t-system to the C—X bond in the monosubstituted radical anions proposed as intermediates [19]. 

After the enamine has been used as a nucleophile, it can easily be hydrolyzed back to the ketone and the secondary amine by treatment with aqueous acid. This is simply the reverse of the process used to prepare it. Overall, enamines serve as the synthetic equivalent of ketone enolate anions. Examples are provided in the following equations ... 

The Claisen-type condensation of ketone enolate anions and arenesulfinates provides an interesting synthetic approach to diastereomeric ji-oxo sulfoxides69,70. 

As with ketone enolate anions (see 16-34), the use of amide bases under kinetic control conditions (strong base with a weak conjugate acid, aprotic solvents, low temperatures), allows the mixed Claisen condensation to proceed. Self-condensation of the lithium enolate with the parent ester is a problem when LDA is used as a base, ° but this is minimized with LICA (lithium isopropylcyclohexyl amide).Note that solvent-free Claisen condensation reactions have been reported. ° ... 

Minami, T., Watanabe, K., and Hirakawa, K., A new synthesis of fused heterocychc and carbocychc compounds via the reaction of the vinylphosphonate with imide and ketone enolate anions, Chem. Lett., 2027, 1986. 

An ester enolate is formed by reaction with a strong base, and the resulting enolate anion can condense with an aldehyde, a ketone, or another ester. Ester enolates react with aldehydes or ketones to form P-hydroxy esters. Aldehyde or ketone enolate anions react with esters to form p-hydroxy esters, 1,3-diketones, or p-keto aldehydes. 

An ester enolate is formed by reaction with a strong base, and the resulting enolate anion can condense with an aldehyde, a ketone, or another ester. Ester enolates react with aldehydes or ketones to form p-hydroxy esters. Aldehyde or ketone enolate anions react with esters to form p-hydroxy esters, 1,3-diketones, or p-keto aldehydes 56,57,84,99,100,102,108,110,114,115. Enolate anions react as nucleophiles. They give nucleophilic acyl substitution reactions with acid derivatives. The condensation reaction of one ester with another is called a Claisen condensation and it generates a P-keto ester. A mixed Claisen condensation under thermodynamic conditions leads to a mixture of products, but kinetic control conditions can give a single product 52, 53, 54, 55, 59, 68, 69,98,99,101,125. 

Recently, the syntheses of six- to nine-manbaed baizo-fused hetOTOcycles 98 in good to excellent yields were reported [78]. The synthetic approach involves the photostimulated reaction of ketone enolate anions 96, prepared from ketones 95, linked by a bridgeZ to apendant haloarene (Scheme 10.13). 

Nearly all the reported attempts at ionic copolymerization of vinyl ketones led to polymers containing very high ketone content, even when the comonomer was known to homopolymerize under the conditions. Copolymerization of phenyl vinyl ketone and styrene in bulk or in tetrahydrofuran initiated with n-butyllithium produced only poly(phenyl vinyl ketone) [341]. The non-incorporation of styrene in the anionic copolymerization was due to the phenyl vinyl ketone enolate anion being sufficiently nucleophilic to add the phenyl vinyl ketone monomer but not the styrene. 

Trimethylsilyl enol ethers are formed readily from ketones (Eqs. 6.38 and 6.39) and are especially valuable nucleophiles toward a variety of electrophilic carbon species [33]. After attachment of the electrophilic carbon, the trimethylsilyl group is readily removed to afford a ketone. Alkylation is achieved with the use of a Lewis acid catalyst (Eq. 7.18) [34]. The reaction is analogous to the alkylation of a ketone enolate anion. 

---