Step 1. Malonic acid dichloride: 8.0 g (76.9 mmol) of malonic acid and 30.0 g (0.25 ) of thionyl chloride were first heated at 50C for 3 days, then at 60C for 6 hours.
mol) of thionyl chloride were heated at 50C for 3 days, then at 60C for 6 hours.
After removing the thionyl chloride in a rotary evaporator, the residue was distilled. Yield: 6.3 g (58%), oil, boiling point 43 C / 12 Torr.
Step 2, Di-tert-butyl malonate: to a solution of 19.5 g (0.26 mol) of anhydrous tert-butanol in 20 mL of anhydrous N,N-dimethylaniline was added dropwise at room temperature a solution dissolved in 6.0
g (0.43 mmol) of malonic acid dichloride in a 15 mL solution of anhydrous CHCl3. Subsequently, the solution was heated at reflux for 4 hours and 40 mL of
3M sulfuric acid was added to the cooled solution. The aqueous phase was extracted three times with 50 mL of ether. The combined organic phases were washed with 20 mL of water, 20 mL of saturated aqueous potassium carbonate solution, and 20 mL of saturated sodium chloride solution.
The ether phase was dried over magnesium sulfate and filtered. The solvent was evaporated and the residue was distilled. Yield: 6.0 g (62%), bp 93 C/ 10 Torr.
