Propanedioate esters, acidity alkylation

The anions of esters such as ethyl 3-oxobutanoate and diethyl propanedioate can be alkylated with alkyl halides. These reactions are important for the synthesis of carboxylic acids and ketones and are similar in character to the alkylation of ketones discussed previously (Section 17-4A). The ester is converted by a strong base to the enolate anion, Equation 18-18, which then is alkylated in an SN2 reaction with the alkyl halide, Equation 18-19. Usually, C-alkylation predominates ... 

Esters of propanedioic (malonic) acid can be alkylated in a similar fashion (Equation 18-20) ... 

Alkyl-substituted 3-oxobutanoic and propanedioic esters can be hydrolyzed under acidic conditions to the corresponding acids, and when these are heated they readily decarboxylate (Section 18-4). Alkyl 3-oxobutanoic esters thus yield methyl alkyl ketones, whereas alkylpropanedioic esters produce carboxylic acids ... 

In Section 23-2 two reactions of /3-tlicarbonyl compoiiiiJs arc presented. The (irst is alkylation of the readily deprotonated "carbon in the middle." The second pertains to /3-dicarbonyi compounds where at least one of the carbonyl groups is an ester. Ester hydrolysis leads to a carboxylic acid that readily loses COi (decarboxylation). When this sequence is carried out on a /3-ketocster, the result is a ketone. When carried out on a diester of propanedioic (malonic) acid, the result is a carboxylic acid. In each case, groups attached in the preliminary alkylation slep(s) wind up in the product. 

Diethyl propanedioate, commonly called diethyl malonate or malonic ester, is more acidic than monocarbonyl compounds pK =13) because its a hydrogens are flanked by two carbonyl groups. Thus, malonic ester is easih converted into its enolate ion by reaction with sodium ethoxide in ethanol. The enolate ion, in turn, is a good nucleophile that reacts rapidh with an alkyl halide to give an a-substituted malonic ester. Note in the following examples that the abbreviation "Et" is used for an ethyl group, CH2CH3. 

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