Halides, alkyl, reaction with ester dianions

The dianions of /S-enamino ketones react with a wide range of electrophiles such as alkyl halides, oxiranes, nitriles, esters, aldehydes and ketones37. Dalpozzo and coworkers reported the generation of the dianion derived from /S-enamino ketones with lithium 2,2,6,6-tetramethylpiperidide and the reaction of the dianion with nitroalkene (Scheme 24)38. The dianion underwent exclusive alkylation at the y-carbon atom to give the monoalkylated product in high yield. This reaction is useful for the introduction of a nitro group into a ketone side chain. 

Allylic 3-(benzotriazoM-yl)-3-ethoxyalkenes are conjugated acyl anion equivalents. Thus, deprotonation with BuLi and reaction with alkyl halides or esters furnish enones and unsaturated a-diketones," respectively. l-(Benzotriazol-l-yl)-3-(diphenylphosphoryl)-l-ethoxy-l-propene is a propanoic ester P, 3-dianion equivalent. 

A re-investigation of the reaction between diketen and amides has shown that N-acetoacetylcarboxamides are formed most efficiently in the presence of trimethylsilyliodide. Olefins react with primary amides in the presence of mercury(ii) nitrate to give iV-substituted amides after NaBH4 reduction. The method provides a convenient procedure for the Markovnikov amidation of double bonds yields vary from 17 to 99% over 11 examples. Direct C-alkylation of secondary thioamides is achieved by the reaction of the dianion (177) with an activated halide to give (178). Esters of malonic, cyanoacetic, and /8-keto acids are readily C-amidoethylated by N-acylaziridines in the presence of triethylamine. ... 

Deprotonation and Alkylation Reactions. Reaction of the title compound with LDA and trapping of the resulting ester enolate with alkyl halides leads to mixtures of the a- and p-alkylated products (eq 1), the ratio of which can be strongly influenced by the presence or absence of Cul. Related studies have been carried out on the dianion derived from the precursor acid, and one product of such processes exploited in the synthesis of the racemic modification of the diterpene trixagol. ... 

Carboxylic acids can be alkylated in the a position by conversion of their salts to dianions [which actually have the enolate structures RCH=C(0 )21497] by treatment with a strong base such as lithium diisopropylamide.1498 The use of Li as the counterion is important, because it increases the solubility of the dianionic salt. The reaction has been applied1499 to primary alkyl, allylic, and benzylic halides, and to carboxylic acids of the form RCHjCOOH and RR"CHCOOH.1454 This method, which is an example of the alkylation of a dianion at its more nucleophilic position (see p. 368), is an alternative to the malonic ester synthesis (0-94) as a means of preparing carboxylic acids and has the advantage that acids of the form RR R"CCOOH can also be prepared. In a related reaction, methylated aromatic acids can be alkylated at the methyl group by a similar procedure.1500... 

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. 

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