Method A: 24.6 mmol of ethyl 3-bromopyruvate was slowly added to a 47 mL solution of isopropanol containing 5.0 g (24.2 mmol) of tert-butyl (2-amino-2-thioethyl)carbamate at 20-25 °C. The reaction mixture was stirred continuously at this temperature for 5 hours. Subsequently, 24.0 mmol of a 20% aqueous sodium hydroxide solution was added to the reaction system. Upon completion of the reaction, the organic phase was separated by extraction using methyl tert-butyl ether. The organic phase was washed sequentially with water and saturated sodium chloride solution and dried over anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure to give 6.2 g of ethyl 2-((tert-butoxycarbonylamino)methyl)thiazole-4-carboxylate in 89.6% yield. The product was characterized by 1H-NMR (DMSO-d6, ppm): 8.41 (s, 1H, Ar-H), 7.86 (t, br, NH), 4.41 (d, 2H, CH2), 4.30 (q, 2H, CH2), 1.40 (s, 9H, tert-butyl), 1.30 (t, 3H, CH3).
