Chloroacetyl chloride → 5-methyl-1H-pyrido[2,3-b][1,4]oxazin-2-one

3-amino-5-methyl-pyridin-2-ol (1.32 g, 10.6 mmol) was dissolved in 50 ml of anhydrous N,N-dimethyl formamide under nitrogen atmosphere, and chloroacetyl chloride solution (1.02 ml, 12.72 mmol) was added thereto dropwise at room temperature. After stirring for 30 minutes, potassium carbonate (3.7 g, 26.5 mmol) was added thereto dropwise at room temperature, and the reaction mixture was heated to 100□ and then stirred for 18 hours. The reaction mixture was cooled to room temperature and the reaction was quenched by adding water. The organic layer was extracted with ethyl acetate, and the combined organic layer was washed with water and saturated saline solution, dried over anhydrous sodium sulfate (Na2SO4), filtered and evaporated under reduced pressure to obtain straw yellow solid (424 mg). The resulting solid was used in the next step without further purification.