Malonic ester synthesis is a synthetic procedure used to convert a compound that has the general structural formula 1 into a carboxylic acid that has the general structural formula 2.
R1 = alkyl group
L = leaving group
The group —CH2CO2H in 2 is contributed by a malonic ester, hence the term malonic ester synthesis.
R2 = alkyl, aryl
Malonic ester synthesis consists of four consecutive reactions that can be carried out in the same pot.
reaction 1: acid-base reaction
reaction 2: nucleophilic substitution
reaction 3: ester hydrolysis (using saponification)
reaction 4: decarboxylation
eg:
reaction 1:
reaction 2:
reaction 3:
reaction 4:
A more direct method to convert 3 into 4 is the reaction of 3 with the enolate ion (5) of ethyl acetate followed by hydrolysis of the resultant ester.
However, the generation of 5 from ethyl acetate quantitatively in high yield is not an easy task because the reaction requires a very strong base, such as LDA, and must be carried out at very low temperature under strictly anhydrous conditions.
Malonic ester synthesis provides a more convenient alternative to convert 3 to 4.
Malonic ester synthesis can be adapted to synthesize compounds that have the general structural formula 6.
R3, R4 = identical or different alkyl groups
eg:
reaction 1:
reaction 2:
reaction 1 (repeat):
reaction 2 (repeat):
reaction 3:
reaction 4:
see also acetoacetic ester synthesis
