General procedure for the synthesis of ethyl 2-chlorooxazole-5-carboxylate from ethyl oxazole-5-carboxylate: to a solution of ethyl oxazole-5-carboxylate (15.0 g, 106 mmol) in tetrahydrofuran (THF, 150 mL) was added slowly and dropwise to a solution of lithium hexamethyldisilanamide (LiHMDS, 178 mL, 170 mmol) at -60 °C. The reaction mixture was stirred continuously at -50 °C for 1 hour. Subsequently, hexachloroethane (37.8 g, 160 mmol) was added to the reaction system. The reaction mixture was warmed to room temperature and stirred for 12 hours. Upon completion of the reaction, the reaction was quenched with saturated aqueous ammonium chloride (NH4Cl) solution (50 mL) and subsequently extracted with ethyl acetate (EtOAc, 50 mL). The organic layer was separated, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The residue was purified by column chromatography to afford the target product ethyl 2-chlorooxazole-5-carboxylate (10 g, 56% yield) as a colorless oil.1H NMR (400 MHz, CDCl3) δ 7.71 (s, 1H), 3.39 (q, J=7.2 Hz, 2H), 1.38 (t, J=7.2 Hz, 3H).
