To a three-necked round-bottomed flask equipped with a magnetic stirrer was added 1,4-dioxane (6.8 mL), triethylamine (2.96 g, 0.0293 mol) and ethyl vinyl ether (7.37 g, 0.102 mol). The reaction mixture was slowly heated to 30 °C under nitrogen protection. Ethyl chlorooxyacetate (2.73 g, 0.02 mol) was added dropwise over a period of 5 minutes using a syringe, followed by stirring the reaction system for 2 hours while maintaining the reaction system at 33-36°C. After completion of the reaction, the mixture was cooled to room temperature and insoluble solids were removed by filtration. The crude product obtained by concentrating the filtrate was dissolved in water (15 mL) and extracted with ethyl acetate (15 mL). The organic layers were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to give ethyl 4-ethoxy-2-oxo-3-butenoate as a light brown oil (3.02 g, 87.8% yield). The product was characterized by 1H NMR (CDCl3): δ 7.86 (d, 1H, J = 12.6 Hz), 6.17 (d, 1H, J = 12.6 Hz), 4.30 (q, 2H, J = 7.1 Hz), 4.05 (q, 2H, J = 7.1 Hz), 1.36 (m, 6H).
