GENERAL STEPS: (a) Under argon protection, n-butyllithium (24 mL, 0.06 mol, 2.5 M hexane solution) was dissolved in 50 mL of ether and cooled to -78°C. Subsequently, a solution of 5-methylthiazole (5 g, 0.05 mol) dissolved in 25 mL of ether was added slowly and dropwise. The reaction mixture was stirred continuously at -78°C for 1 hour. Next, a solution of N-formylmorpholine (5.5 mL, 0.055 mol) dissolved in 30 mL of ether was added dropwise over 15 minutes. After addition, the mixture was continued to be stirred at -78°C for 1 hour, followed by warming to 0°-5°C and stirring overnight. Upon completion of the reaction, the reaction mixture was extracted with 4N HCl (4 x 10 mL), the aqueous phases were combined, cooled in an ice bath, and adjusted with sodium bicarbonate solution to pH 9. The aqueous phase was then extracted with ether (4 x 20 mL), the organic phases were combined, dried with magnesium sulfate, and concentrated under reduced pressure. The residue was dried under vacuum to give 4.5 g of 5-methyl-2-thiazolecarboxaldehyde in 70.8% yield.
