It's diethyl ester (diethyl malonate) is more important commercially.

C-Acylation of malonic esters is normally carried out by reaction of the Mg derivative with an acid chloride. A convenient method using a combination of MgCl2 and triethylamine was introduced by Rathke: J. Org. Chem., 50, 2622 (1985); see also for discussion of this system:

malonic acid | C3H4O4 - PubChem

The principal synthetic utility of the malonate esters may be summarized as follows:
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malonic acid | C3H4O4 | CID 867 ..

For phase-transfer monoalkylation of the active methylene group see, e.g. (18-crown-6): Synthesis, 37 (1977); and (BTEAC): Org. Prep. Proced. Int., 26, 469 (1994). Solid-liquid phase transfer alkylation has been promoted by microwave irradiation: Synth. Commun., 25,1761 (1995). Dialkylation can also occur in the presence of BTEAC: Synthesis, 54 (1985); Org. Synth. Coll., 7, 411 (1990), to give cyclopropane derivatives. Stereoselective alkylation has been achieved under particularly mild conditions with secondary alkyl mesylates in the presence of in DMF; complete inversion occurs at the secondary alkyl carbon: J. Org. Chem., 60, 2627 (1995); see also: Synlett, 499 (1998). Substituents can also be introduced by Michael addition; see e.g.: Org. Synth. Coll., 8, 467 (1993). Arylation occurs with aryl bromides in the presence of CuI: Gazz. Chim. Ital., 122, 511 (1992). C-Acylation of malonic esters is normally carried out by reaction of the Mg derivative with an acid chloride. A convenient method using a combination of MgCl2 and triethylamine was introduced by Rathke: J. Org. Chem., 50, 2622 (1985); see also for discussion of this system: A number of procedures have been devised for the direct conversion of malonic esters to acetic esters (decarboalkoxylation), in a single step of which heating in wet DMSO is perhaps the simplest: J. Org. Chem., 43, 138 (1978). See also . Compare also , , , and . Semmes, J. G.; Bevans, S. L.; Mullins, C. H.; Shaughnessy, K. H. Arylation of diethyl malonate and ethyl cyanoacetate catalyzed by palladium/di-tert-butylneopentylphosphine. Tetrahedron Lett. 2015, 56 (23), 3447-3450.Ramesh, P.; Shalini, B.; Fadnavis, N. W. Knoevenagel condensation of diethylmalonate with aldehydes catalyzed by immobilized bovine serum albumin (BSA). RSC Adv. 2014, 4 (15), 7368-7373.

For example, diethyl malonate is malonic acid's ethyl ester

Diethyl malonate is used in organic synthesis for the preparation of alpha-aryl malonates, mono-substituted and di-substituted acetic acid, barbiturates and artificial flavorings. It is also involved in the synthesis of pharmaceuticals like chloroquine, butazolidin and barbital. It acts as intermediate in the synthesis of vitamin B1, vitamin B6, non-steroidal anti-inflammatory agents agrochemicals and perfumes. In Knoevenagel condensation reaction, it reacts with benzaldehyde to get diethyl benzylidenemalonate.

It can be derived by oxidizing malic acid or by the hydrolysis of cyanacetic acid.
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Diethyl malonate CAS#: 105-53-3 - ChemicalBook

Mao, J.; Liu, D.; Li, Y.; Zhao, J.; Rong, G.; Yan, H.; Zhang, G. Temperature-controlled NaI-mediated α-oxybenzoylation or oxyacylation-decarboxylation reactions of dimethyl malonate with carboxylic acids. Catal. Commun. 2015, 70, 62-65.

Synthesis of DIETHYL DIETHYLMALONATE - …

In many syntheses reported in the literature, malonates react at both the methylene group and the ester functions, which make them very useful reagents, especially in the formation of heterocycles.

Malonic Ester Synthesis Reaction Mechanism - YouTube

Preparative Methods: is prepared by refluxing with benzyl alcohol with catalytic amount of . is usually obtained from and isobutene with catalytic amount of . tert-Butyl methyl and tert-butyl ethyl malonates can be obtained through reaction of methyl and ethyl malonyl chlorides with , e.g. over activated as a catalyst.a Unsymmetrical methyl, ethyl, and benzyl malonates may be prepared by reaction of the corresponding monoalkyl malonates with alkyl chloroformates.b