Ethyl acetoacetic ester synthesis

Section 21 6 The acetoacetic ester synthesis is a procedure in which ethyl acetoac etate is alkylated with an alkyl halide as the first step in the preparation... 

Acetoacetic ester synthesis (Section 21 6) A synthetic method for the preparation of ketones in which alkylation of the enolate of ethyl acetoacetate... 

The cyclic /3-keto ester produced in a Dieckmann cyclization can be further alkylated and decarboxylated by a series of reactions analogous to those used in the acetoacetic ester synthesis (Section 22.7). For example, alkylation and subsequent decarboxylation of ethyl 2-oxocyclohexanecarboxylate yields a 2-alkylcvclohexanone. The overall sequence of (1) Dieckmann cyclization, (2) /3-keto ester alkylation, and (3) decarboxylation is a powerful method for preparing 2-substituted cyclohexanones and cyclopentanones. 

The esters of nitrous acid are characterised by their high velocities of formation and hydrolysis. They are almost instantaneously decomposed by mineral acids and in the method of preparation given this has been taken into account. The slightest excess of hydrochloric acid must be avoided. Advantage is taken of this property of the alkyl nitrites in all cases where it is desired to liberate nitrous acid in organic solvents (in which metallic nitrites are insoluble). Examples addition of N203 to olefines, preparation of solid diazonium salts (p. 286), production of isonitroso-derivatives from ketones by the action of HN02. This synthesis is often also carried out in the manner of the acetoacetic ester synthesis, with ketone, alkyl nitrite, and sodium ethylate the sodium salt of the isonitrosoketone is formed (cf. in this connexion p. 259) ... 

Alkylation of the enolate anion derived from ethyl acetoacetate followed by removal of the ester group is known as the acetoacetic ester synthesis and is an excellent method for the preparation of methyl ketones. The product of an acetoacetic ester synthesis is the same as the product that would be produced by the addition of the same... 

Although the acetoacetic ester synthesis and the malonic ester synthesis are used to prepare ketones and carboxylic acids, the same alkylation, without the hydrolysis and decarboxylation steps, can be employed to prepare substituted /3-ketoesters and /3-diesters. In fact, any compound with two anion stabilizing groups on the same carbon can be deprotonated and then alkylated by the same general procedure. Several examples are shown in the following equations. The first example shows the alkylation of a /3-ketoester. Close examination shows the similarity of the starting material to ethyl acetoacetate. Although sodium hydride is used as a base in this example, sodium ethoxide could also be employed. 

The acetoacetic ester synthesis is similar to the malonic ester synthesis, but the final products are ketones specifically, substituted derivatives of acetone. In the acetoacetic ester synthesis, substituents are added to the enolate ion of ethyl acetoacetate (acetoacetic ester), followed by hydrolysis and decarboxylation to produce an alkylated derivative of acetone. 

Monoalkylation of ethyl acetoacetate and subsequent ketonic hydrolysis gives methyl ketones of the type CHjCOCHjR (acetoacetic ester synthesis). 

The acetoacetic ester synthesis is a stepwise method for converting ethyl acetoacetate into a ketone having one or two alkyl groups on the a carbon. 

The acetoacetic ester synthesis and direct enolate alkylation are two different methods that prepare similar ketones. 2-Butanone, for example, can be synthesized from acetone by direct enolate alkylation with CH3I (Method [1]), or by alkylation of ethyl acetoacetate followed by hydrolysis and decarboxylation (Method [2]). 

One of the most valuable methods of preparing ketones makes use of ethyl acetoacetate acetoacetic ester), CH3COCH2COOC2H5, and is called the acetoacetic ester synthesis of ketones. This synthesis closely parallels the malonic ester synthesis of carboxylic acids. 

Problem 26.7 (a) Predict the product of the acetoacetic ester synthesis in which ethyl bromoacetate (why not bromoacetic acUH) is used as the halide. To what general class of compounds does this product belong (b) Predict the product of the acelo-acelic ester synthesis in which benzoyl chloride is used as the halide in which chloro-acetone is used as the halide. To what general classes of compounds do these products belong ... 

Acetoacetic ester synthesis, 839—841, 850. See also Ethyl acetoacetate Acetoacetyl acyl carrier protein, 1021 Acetoacetyl coenzyme A, 1021, 1032 Acetone... 

The second classical reaction mentioned above is the acetoacetic ester synthesis. this reaction, an ester of acetoacetic acid (3-oxobutanoic acid) such as ethyl acetoacetate is treated with base under thermodynamic control conditions and alkylated, as with the malonic ester synthesis. Reaction with sodium ethoxide in ethanol (since an ethyl ester is being used) generated the enolate and quenching with benzyl bromide led to 84. Saponification and decarboxylation (as above) gave a substituted ketone (85). Although the malonic ester synthesis and the acetoacetic ester synthesis are fundamentally similar, the different substrates lead to formation of either a highly substituted acid or a ketone. The reaction is not restricted to acetoacetate derivatives, and any p-keto-ester can be used (ethyl 3-oxopentanoate for example). ... 

Variations of the malonic ester and acetoacetic ester sequenees lead to many useful synthetic opportunities. In the examples quoted, the base-solvent pair used was ethanol-sodium ethoxide, where the alkoxide is the conjugate base of tbe solvent. If NaOEt-EtOH were used with a methyl ester, transesterification would give a mixture of methyl and ethyl esters as products. For both malonic ester and acetoacetic ester removal of the most acidic proton (a to both carbonyls) also gives the more thermodynamically stable enolate. Either NaOEt-EtOH or LDA-THF will generate the desired enolate. The malonic ester synthesis is most useful for the synthesis of highly substituted monoacids, and tbe acetoacetic ester synthesis is used to prepare substituted methyl ketones. 

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