Di-tert-butyl methylenemalonate (CAS no ), which is also known as dioic acid, methylene-, bis(1,1-dimethylethyl)estere, could be produced through the following synthetic routes.

A 250-mL, one-necked, round-bottomed flask is equipped with a magnetic stirrer and a reflux condenser protected by a calcium chloride drying tube. Into the flask are placed 30.0 g (0.14 mol) of di-tert-butyl malonate, 8.4 g (0.28 mol) paraformaldehyde, 1.4 g (0.014 mol) of potassium acetate, 1.4 g (0.007 mol) of cupric acetate monohydrate, and 70 mL of glacial acetic acid. The resulting green–white suspension is placed in an oil bath preheated to 90–100°C and stirred for 2 hr. The reaction mixture is allowed to cool to room temperature, and the reflux condenser is replaced with a short-path distillation apparatus, the vacuum outlet of which is connected in sequence to a trap cooled in acetone–dry ice, a potassium hydroxide trap, another trap cooled in acetone–dry ice, and a vacuum pump. The receiving flask is cooled in acetone–dry ice, and the system is evacuated over approximately 1 hr to remove acetic acid and other volatile material. The bath temperature is increased to 40–50°C for 15 min and then is rapidly raised to 140–150°C to drive over crude product, which is collected over a boiling-point range of 60–82°C. When distillate ceases to come over, the bath temperature is increased to 170°C and distillate is collected over the same boiling-point range until the reaction mixture turns from blue to green–brown. The total amount of crude product collected is 24.3 g. This material is dissolved in 50 mL of ether and washed with saturated aqueous sodium bicarbonate solution (4 × 20 mL) and water (25 mL). The combined aqueous fractions are extracted with 50 mL of ether, and the combined ether extracts are dried over magnesium sulfate for 10 min. Filtration and evaporation on a rotary evaporator give 20.0 g of crude product, which is distilled through an 8-cm Vigreux column. The di-tert-butyl methylenemalonate is collected at 60–67°C/0.1 mm and weighs 15.3 g (48%). The product is somewhat unstable and should be stored in Pyrex in the refrigerator.

Notice: This reaction should be carried out in an efficient hood to prevent exposure to formaldehyde and acetic acid.