Diethyl malonate (also known as DEM) is a versatile compound that finds numerous applications in organic synthesis. It is an ester derivative of malonic acid and contains two ester groups. The presence of these ester groups makes diethyl malonate a valuable building block in various chemical reactions. Here are some common applications of diethyl malonate in organic synthesis:

1. Malonic Ester Synthesis: Diethyl malonate is widely used in the malonic ester synthesis, which is a powerful method to introduce a carboxylic acid group into organic molecules. In this reaction, diethyl malonate undergoes nucleophilic substitution with alkyl halides or other electrophiles to form substituted malonic esters. The resulting malonic esters can be further modified through decarboxylation, hydrolysis, or other chemical transformations.

2. Knoevenagel Condensation: Diethyl malonate participates in the Knoevenagel condensation reaction, which is a useful carbon-carbon bond-forming reaction. It reacts with aldehydes or ketones in the presence of a base to give α,β-unsaturated carboxylic acids or their derivatives. This reaction is widely employed in the synthesis of a variety of compounds, including pharmaceuticals, dyes, and natural products.

3. Synthesis of Barbiturates: Diethyl malonate serves as a key starting material in the synthesis of barbiturates, which are a class of drugs with sedative, hypnotic, and anticonvulsant properties. By reacting diethyl malonate with urea and an appropriate aldehyde or ketone, barbiturate derivatives can be obtained.

4. Synthesis of α-Amino Acids: Diethyl malonate can be used for the synthesis of α-amino acids through a multi-step reaction sequence known as the malonic ester synthesis. By selectively alkylating one ester group, followed by hydrolysis, decarboxylation, and further modifications, α-amino acids with various side chains can be obtained.

5. Synthesis of Heterocycles: Diethyl malonate participates in the synthesis of various heterocyclic compounds. For example, it can undergo cyclization reactions, such as the Dieckmann condensation, to form five- or six-membered rings. These reactions are useful for the synthesis of natural products, pharmaceuticals, and other biologically active compounds.