Diethyl oxomalonate (also known as diethyl mesoxalate, diethyl ketomalonate, or diethyl 2-oxomalonate) is the diethyl ester of mesoxalic acid (ketomalonic acid). It is a chemical compound with the molecular formula C₇H₁₀O₅ and a molecular weight of 174.15 g/mol. Its preferred IUPAC name is diethyl oxopropanedioate.
Structure and Properties
Diethyl oxomalonate is an α-keto ester featuring a highly electrophilic central carbonyl group, making it a versatile and reactive building block in organic synthesis. It appears as a greenish-yellow, low-viscosity, low-odor oil. At humid air, it reacts with water to form the crystalline dihydrate (white prisms). Its refractive index is approximately 1.425–1.431 (at 20–22 °C, 589 nm). It is soluble in ethanol, diethyl ether, and chloroform.
Production
The compound was first synthesized in pure form in 1892 by Richard Anschütz and co-workers, starting from the decomposition of the barium salt of alloxan to oxomalonic acid, followed by esterification with ethanol. Other synthetic routes include:
- Nitrosation/oxidation: Nitrosation of diethyl malonate followed by oxidation with dinitrogen tetroxide (N₂O₄) or dinitrogen trioxide (N₂O₃).
- Ozonolysis: Ozonolysis of diethyl benzalmalonate or diethyl ethylidenemalonate.
- Photooxygenation: Photooxygenation of enamine products from dimethylformamide dimethyl acetal.
- Oxidation with sodium chlorite: A more recent method using aqueous NaClO₂ at pH 4.4, achieving up to 97% yield from diethyl malonate.
Reactivity and Applications
Due to its strongly polarized keto group, diethyl oxomalonate acts as an electrophile in addition reactions and is highly active in pericyclic reactions:
- Diels–Alder reactions: It serves as an electron-poor dienophile and can be used as a carbon dioxide equivalent in [4+2] cycloadditions with electron-rich 1,3-dienes (e.g., isoprenes, dimethyl butadienes) to form geminal dihydropyran diesters.
- Aldol additions: Reacts with enamines to form α-hydroxy-γ-ketodiesters, which can be converted to substituted butenolides.
- Imidazolone synthesis: With guanidines, it produces functionalized imidazolones in up to 85% yield.
- Baylis–Hillman reaction: A fast-reacting substrate with acrylates, acrylonitrile, or methyl vinyl ketone catalyzed by DABCO.
- Ene reactions: Adds to terminal double bonds of alkenes to give 1-hydroxy-1-alkylmalonic esters.
- Grignard reactions: Reacts with organomagnesium compounds to form isobenzofuran derivatives.
Safety and Handling
Diethyl oxomalonate is classified under GHS labeling with appropriate hazard and precautionary statements. It should be handled in a well-ventilated area with standard laboratory safety precautions.
References
- Tietze, T.F.; Schneider, C.; Coughlin, D.J. (2009). "Diethyl Oxomalonate". E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rd207m.pub2.
- Anschütz, R.; Parlato, E. (1892). "Ueber den Oxomalonsäureäthylester". Chemische Berichte. 25 (2): 3614–3617. doi:10.1002/cber.189202502245.
- PubChem CID 69105. "1,3-Diethyl 2-oxopropanedioate". National Center for Biotechnology Information.
- CAS Number: 609-09-6.
