Step 2: Synthesis of 6-bromo-4,4-dimethyl-1,4-dihydro-2H-3,1-benzoxazin-2-one; the compound was prepared with reference to U.S. Patent No. 4,522,576 and U.S. Patent No. 6,444,668. to an anhydrous nitrogen-protected 2-(2-amino-5-bromophenyl)propan-2-ol (18 g, 78 mmol) THF (150 mL) solution was added N,N'-carbonyldiimidazole (15.5 g, 94 mmol). The reaction mixture was heated and stirred at 50 °C overnight. After completion of the reaction, the solvent was removed by distillation under reduced pressure and the residue was dissolved in ethyl acetate (100 mL). The resulting solution was washed sequentially with 1N HCl (2 × 40 mL), brine (20 mL), dried over anhydrous MgSO4 and filtered. The filtrate was concentrated under reduced pressure to give 6-bromo-4,4-dimethyl-1,4-dihydro-2H-3,1-benzoxazin-2-one (20 g, 100% yield) as a white solid with a melting point of 199-200 °C.
