General Procedure for the Preparation of Ethyl-2-Aminothiazole-4-Carboxylate (3)

A mixture of ethyl bromopyruvate (0.05 mol, 9.75 g) and thiourea (0.10 mol, 7.61 g) in absolute ethanol (53mL) was refluxed for 24 h. The completion of the reaction was checked by thin layer chromatography (TLC). After completion, the reaction mixture was allowed to cool to room temperature and concentrated in vacuo to half the original volume. The remaining ethanol solution was poured into water and made alkaline (pH 10) with 2N NaOH. Light brown solid precipitated immediately. The mixture was stirred for about 10 min and then the solid was removed by vacuum filtration and dried to give the desired product.47

Light brown crystals; yield: 68%; m.p. found: 176 °C; m.p. reported: 175–180 °C; R_f = 0.18 (pet.ether:ethyl acetate 3:1); FTIR (ν_max cm⁻¹) 3290 (NH₂, str.), 1733 (C=O, ester, str.), 1615 (C=N, str.), 1540 (C=C, str.); ¹H NMR (400 MHz, CD₃OD) δ ppm 7.4 (s, 1H, H-1), 5.8 (brs, 2H, NH₂), 4.32 (q, J=7.2Hz, 2H, H-2), 1.35 (t, J=7.2Hz, 3H, H-3); ¹³C NMR (400 MHz, CD₃OD) δ ppm 167.8, 161.5, 148.2, 116.7, 61.3, 15.2; Anal. calcd for C₆H₈O₂N₂S (172.20): C, 41.86; N, 16.27; H, 4.68. Found: C, 41.79; N, 16.19; H, 4.61%.