The general procedure for the synthesis of ethyl 3-cyclobutyl-3-oxopropanoate from monoethyl malonate potassium salt and cyclobutanecarbonyl chloride was as follows: potassium 3-ethoxy-3-oxopropanoate (60.3 g, 354.25 mmol) was suspended in acetonitrile (600 mL) under the protection of argon gas and cooled to 10 °C. Subsequently, triethylamine (75 mL, 540 mmol) and magnesium chloride (40.2 g, 421.72 mmol) were added sequentially, and the reaction temperature was controlled not to exceed 25 °C. The resulting thick white suspension was stirred at room temperature for 2.5 hours in an argon atmosphere. After that, the reaction mixture was cooled to 0-5 °C again and cyclobutanecarbonyl chloride (19.25 mL, 167 mmol) was added slowly dropwise for a controlled period of 1 hour. After the dropwise addition, the reaction mixture was allowed to gradually warm up to room temperature and continued stirring for 18 hours. After completion of the reaction, the solvent was removed by evaporation. The residue was dissolved in ethyl acetate (700 mL) and adjusted to an aqueous phase pH=5 with 2M hydrochloric acid (~400 mL) to ensure that all substances were dissolved. The organic phase was separated and washed sequentially with 2M hydrochloric acid (200 mL), saturated aqueous sodium bicarbonate (2 x 200 mL). The organic layer was dried over anhydrous magnesium sulfate, filtered and concentrated to afford ethyl 3-cyclobutyl-3-oxopropionate as a light yellow oil (28.0 g, 98% yield). The structure of the product was confirmed by 1H NMR (400.132 MHz, CDCl3): δ 1.28 (3H, t), 1.80-1.89 (1H, m), 1.91-2.05 (1H, m), 2.12-2.34 (4H, m), 3.39 (2H, s), 3.34-3.42 (1H, m), 4.19 (2H, q).
