Dimethyl mesoxalate (CAS NO.: ), which is also known as dioic acid, oxo-, di, could be produced through the following synthetic routes.

A 300-mL wash bottle with an inlet tube fitted with a wide pore glass frit and equipped with a stirring bar is charged with 40.0 g (0.18 mol) of dimethyl benzalmalonate dissolved in 150 mL of dichloromethane. The cooled solution (0°C, ice bath) is purged with argon (10 min) and then a stream of is passed through with vigorous stirring for 4.5 hr. After the reaction is complete (TLC, silica gel, diethyl ether/petroleum ether = 1:1), excess ozone is removed by purging with argon (10 min) and 15 mL of dimethyl sulfide is slowly added at 0°C (ice bath). Stirring is continued for 1 hr at this temperature and 2 hr at ambient temperature. Finally, air is blown through the solution for 12 hr and the residue is distilled at 20 mm, boiling range 90–100°C to give a yellow liquid that is further purified by filtration through 150 g of silica gel (SiO₂) (elution with diethyl ether). The solvent is removed under reduced pressure and the residue is recrystallized from ethyl acetate to give 23.9 g (80%) of the dimethyl mesoxalate hydrate as colorless crystals. Dehydration of the product is accomplished by azeotropic removal of water. The hydrate is dissolved in dichloromethane (150 mL) and heated for 12 hr in a Soxhlet apparatus equipped with a thimble containing layers of phosphorus pentoxide and basic alumina. The solvent is then evaporated and the residue distilled at reduced pressure to give 20.1 g (76%) of the ester as a yellow liquid [bp 94°C (20 mm)].

Notice: Ozone is extremely toxic and can react explosively with certain oxidizable substances. Ozone also reacts with some compounds to form explosive and shock-sensitive products. Ozone should only be handled by individuals trained in its proper and safe use and all operations should be carried out in a well-ventilated fume hood behind a protective safety shield.