The general procedure for the synthesis of ethyl oxazole-4-carboxylate from ethyl isocyanoylacetate was as follows: formic acid (8.62 mL, 228 mmol) was added in batches to anhydrous THF (200 mL), and the phenomenon of gas escape was observed. The mixture was stirred for 30 min to form a sol. Subsequently, a solution of ethyl isocyanoacetate (25 mL, 228 mmol) and triethylamine (Et3N, 60.5 mL, 434 mmol) was added to the reaction mixture. The mixture was stirred at room temperature for 1 hour and then changed to reflux conditions overnight. After the reaction was completed, the mixture was cooled to room temperature. Water was added and the mixture was extracted with ether (Et2O, 3 times). The organic phases were combined, dried with magnesium sulfate (MgSO4), filtered and concentrated. The residue was purified by fast column chromatography (FC, eluent: ethyl acetate/heptane, ratio graded from 1:5 to 1:3 and finally to 1:1) to afford ethyl oxazole-4-carboxylate (27.2 g, 84% yield). LC-MS analysis resulted in a retention time (tR) = 0.58 min and a mass-to-charge ratio in the electrosprayed positive ion mode (ES+) (m/z) = 142.07 .
