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Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.

Figure1

The reaction proceeds via abstraction of the acidic α hydrogen from a ꞵ-diester to produce a doubly stabilized enolate ion. The nucleophilic enolate attacks the alkyl halide in an SN2 manner to form an alkylated malonic ester intermediate with a new C–C bond. Further treating the intermediate with aqueous acid or base results in the hydrolysis of the two ester groups to give a 1,3-dicarboxylic acid. The resulting ꞵ-diacidis unstable at high temperatures and readily eliminates CO2 through a cyclic six-membered transition state, forming an enol. The enol tautomerizes to its more stable keto form producing a monosubstituted carboxylic acid. However, a disubstituted carboxylic acid is achieved if the deprotonation and alkylation steps are repeated before hydrolysis and decarboxylation.

Tags

AlkylationDiesterEnolate IonMalonic Ester SynthesisCarboxylic AcidsNucleophilic AttackSN2 ReactionAlkylated Malonic EsterHydrolysisDicarboxylic AcidCO2 EliminationEnol TautomerizationKeto FormDisubstituted Carboxylic Acid

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15.34 : Alkylation of β-Diester Enolates: Malonic Ester Synthesis

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15.1 : Reactividad de los enoles

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15.2 : Reactividad de los iones enolato

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15.3 : Tipos de Enoles y Enolatos

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15.4 : Convenciones del mecanismo de enolato

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15.5 : Formación regioselectiva de enolatos

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15.6 : Efectos estereoquímicos de la enolización

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15.10 : α-Halogenación de derivados del ácido carboxílico: descripción general

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15.12 : Reacciones de compuestos α-halocarbonílicos: sustitución nucleofílica

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15.13 : Nitrosación de enoles

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