[C:1]([C:5]1[CH:6]=[CH:7][C:8]2[O:13][CH:12]([CH3:14])[C:11](=[O:15])[NH:10][C:9]=2[CH:16]=1)(=[O:4])[CH2:2][CH3:3].[BrH:17].C(O)(=O)C.Br.[NH+]1C=CC=CC=1.O>C(O)(=O)C>[Br:17][CH:2]([CH3:3])[C:1]([C:5]1[CH:6]=[CH:7][C:8]2[O:13][CH:12]([CH3:14])[C:11](=[O:15])[NH:10][C:9]=2[CH:16]=1)=[O:4]To a solution of 6-propionyl-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine (3.4 g) and 30% hydrogen bromide-acetic acid (10 ml) in acetic acid (50 ml) was added pyridinium hydrobromide perbromide (5.12 g) at ambient temperature and the mixture was stirred for 2 hours at the same temperature. The reaction mixture was poured into water. The resultant precipitate was collected by filtration and dissolved in a mixture of ethyl acetate and tetrahydrofuran. The organic solution was washed with a saturated aqueous solution of sodium bicarbonate and brine. The solvent was dried over magnesium sulfate and removed in vacuo to afford a crystalline residue, which was washed with diisopropyl ether to give 6-(2-bromopropionyl)-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine (3.8 g).
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