Under nitrogen protection, 3,5-dichloro-6-methyl-1,4-oxazol-2-one (45.5 g, 253 mmol) was dissolved with ethyl propargylate (74.4 g, 758 mmol) in toluene (135 mL) and the reaction was stirred for 23 hours at 80 °C. After completion of the reaction, the mixture was cooled to room temperature and the solvent was removed by rotary evaporation. The residue was treated with hexane (400 mL) and a slightly turbid solution containing the target product was decanted and separated from the dark red impurities. Hexane was again removed by rotary evaporation. The crude product was cooled to 0°C and the flask was vortexed intermittently until the product solidified. The solid was washed with a small amount of pentane. The filtrate was cooled and filtered again to remove the undesired yellow solid regional isomer (16 g). The filtrate was concentrated to dryness by rotary evaporation and purified by silica gel chromatography (9:1 heptane/dichloromethane) to give a clarified liquid, which was allowed to solidify (15.4 g, 65.8 mmol, 26% yield). Mass spectrum (ESI) m/z 234.16 (M + 1). 1H NMR (400 MHz, CDCl3) δ ppm 7.55 (s, 1H), 4.39 (q, J = 7.07 Hz, 2H), 2.53 (s, 3H), 1.39 (t, J = 7.14 Hz, 3H).
