Malonic Ester Synthesis

Overall Reaction

This reaction is identical with the acetoacetic ester synthesis, except that we bein wth diethy malonate and end with a carboxylic acid.  Otherwise the chemistry is identical.

Enolate formation and Alkylation - malonic ester synthesis

In the first reaction, the diethyl malonate is deprotonated to form an enolate.  The enolate is then treated with a primary alkyl halide undergoing an SN2 reaction with the enolate.  In these steps we made a substituted malonic ester.  Hence this is referred to as the malonic ester synthesis.

Decarboxylation

If desired the substituted malonic ester can be easily decarboxylated to form a ketone.  Simply heating the ester in acidic water will decarboxylate the malonic esters.

Under these conditions, the ester is first hydrolyzed (acyl substitution) and then decarboxylates.  The decarboxylation is a pericyclic reaction (e.g. Diels Alder and Claisen Rearrangement were the other pericyclic reactions you may have seen in Ochem).  In the end, a substituted carboxylic acid is formed.