Enolate anions, dianions from esters

Looking back on the history of ketone dianion chemistry, one soon notices that dianion species, derived from / -keto esters, have been in continuous steady use in organic synthesis3,4, as shown in Scheme 2. Thus, ethyl acetoacetate can be converted to the corresponding ketone o a -chainon via consecutive proton abstraction reactions. The resulting dienolate anion reacts with a variety of alkyl halides to give products, resulting from exclusive attack at the terminal enolate anions. 

Dianions of this type react with ketones, epoxides,and esters " as well as a wide variety of other electrophiles. As an example, the dilithio anion of 2-methylpropionic acid was condensed with the epoxide moiety in 229 to form an hydroxy acid, which cyclized to form the lactone ring in 230. Since most of the enolates of acid derivatives contain a leaving group, the alkoxide resulting from reaction with an epoxide often displaces that leaving group to give the lactone. 

Ethyl benzoylacetate allowed to react with NaH in tetrahydrofuran, the resulting soln. added to a soln. of 2 equivalents dilithiobenzoylacetone prepared from benzoylacetone and 2 moles Li-diisopropylamide in tetrahydrofuran, and stirred 2 days at room temp. tetraketone. Y 51%. - The enolate salt of the y -keto ester condenses as electrophylic anion with strong nucleophiles such as the dianion of benzoylacetone. F. e. s. T. P. Murray and T. M. Harris, Am. Soc. 94, 8253 (1972) 95, 6865 (1973). 

Unsaturated Esters.—A full report has been published on non-stereoselective approaches to a,/3-unsaturated esters using condensations between aldehydes or ketones and the dithiocarbonate anion (116) or dianion (117) derived from ethyl mercaptoacetate (c/. 1, 193 2, 198). The reactions involve the intermediacy of a,j8-episulphide esters, and give overall yields of between 60 and 80%. The related carbanion (118) displays similar properties. A more stereoselective approach to a,/3-unsaturated esters is the displacement of phosphate groups from enol phosphates by dialkylcuprates (Scheme 42). The dianion derived from... 

A new synthesis of aldehydes with 2-methyl-2-thiazoline has the advantage of releasing the aldehydes from the thiazolidine intermediate under neutral conditions . Acetylene derivatives can be obtained from aldehydes via dibromomethylene compounds Novel reactions of alkynes with cationoid electrophiles have been published. -Diketones and 2-ketoalkoximes can be obtained by this reaction from acid chlorides and aliphatic nitro compounds respectively Addition of aldehydes to activated carbon-carbon double bonds occurs smoothly in the presence of cyanide ions as catalysts . Poly- -carbonyl compounds have been prepared by condensation of two anions, whereby the enolate salt of a y8-keto ester condenses as an electrophilic anion with strong nucleophiles such as the dianion of benzoylacetone. ... 

---