894852-01-8

20348-21-4

894852-01-8

Step (ii): Synthesis of 7-bromo-2,2-dimethyl-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-one (Intermediate-18) To a stirred solution of 2,2-dimethyl-2H-pyrido[3,2-b][1,4]oxazin-3(4H)-one (18.1) (2 g, 11.23 mmol) in dichloromethane (DCM) (20 mL) was added sodium carbonate (Na2CO3) (3.57 g, 33.70 mmol) and bromine (0.92 mL, 17.97 mmol) in turn at 0°C. The solution was purified with aqueous solution of sodium carbonate (Na2CO3) (3.57 g, 33.70 mmol). 17.97 mmol). The reaction mixture was stirred at 20-35°C for 16 hours. Upon completion of the reaction, the reaction mixture was diluted with ice water, the resulting solid was collected by filtration and washed with cold water to afford the target compound as a white solid (1.8 g, 86% yield).1H NMR (400 MHz, DMSO-d6) data were consistent with the expected structure.