Step 1: Synthesis of 5-methylthiazole-4-carboxaldehyde. Ethyl 5-methylthiazole-4-carboxylate (794 mg, 5.05 mmol) was dissolved in anhydrous THF (21.6 mL) under argon protection and cooled to -78 °C. A toluene solution of 1.0 M DIBAL-H (5.56 mL, 5.56 mmol) was added slowly and dropwise, keeping the reaction temperature at -78 °C. The reaction mixture was stirred at this temperature for 30 min. Subsequently, the reaction was quenched with deionized water (12.4 mL) and gradually warmed to room temperature. The reaction mixture was poured into 300 mL of saturated aqueous Rochelle's salt solution and diluted with EtOAc. After vigorous stirring of the mixture for 1 h, the organic and aqueous layers were separated. The aqueous layer was further extracted with EtOAc (3 times). All organic phases were combined, washed with saturated brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The crude product was purified by ISCO column chromatography (eluent: 10% EtOAc in DCM solution) to give 642 mg (54% yield) of the title compound as a yellow oil.NMR (400 MHz, CDCl3) δ 10.22 (s, 1H), 8.62 (s, 1H), 2.83 (s, 3H).
