Under cooling conditions in an ice bath, monoethyl malonate potassium salt (17.0 g, 0.10 mol) was suspended in ethyl acetate (100 ml) and triethylamine (34.7 ml, 0.25 mol) and magnesium chloride (14.3 g, 0.15 mol) were added sequentially. The resulting mixture was stirred and reacted at 40°C for 20 hours. Cyclopropanecarbonyl chloride (4.30 g, 50.0 mmol) was also taken and dissolved in tetrahydrofuran (50 ml), oxalyl chloride (4.36 ml, 50.0 mmol) and a catalytic amount of N,N-dimethylformamide were added under the cooling of an ice bath, stirred for 1 h. After stirring, it was moved to room temperature and the reaction was continued for 1 h. The reaction was continued at room temperature. Subsequently, the previously prepared malonic acid solution was slowly added to this chloride solution under ice bath cooling and the reaction was stirred at room temperature for 20 hours. After completion of the reaction, the mixture was poured into 10% aqueous citric acid solution (300 ml) and extracted with ethyl acetate (300 ml x 3). The organic layers were combined and washed sequentially with saturated aqueous sodium bicarbonate (500 ml) and brine (300 ml) and dried over anhydrous sodium sulfate. The solvent was concentrated under reduced pressure to give ethyl 3-cyclopropyl-3-carbonyl-propionate 7.26 g (93% yield) as a colorless oil, which was used directly in the next reaction.1H-NMR (400 MHz, CDCl3) δ: 0.94-0.99 (2H, m), 1.10-1.15 (2H, m), 1.28 (3H, t, J=7.08 Hz). 2.01-2.06 (1H, m), 3.57 (2H, s), 4.21 (2H, q, J=7.08Hz).
