[NH2:1][C:2]1[CH:12]=[CH:11][C:5]2[NH:6][C:7](=[S:10])[CH2:8][O:9][C:4]=2[C:3]=1[C:13]([O:15][CH3:16])=[O:14].CI.[C:19](=O)([O-])[O-].[K+].[K+]>CC(C)=O>[NH2:1][C:2]1[CH:12]=[CH:11][C:5]2[N:6]=[C:7]([S:10][CH3:19])[CH2:8][O:9][C:4]=2[C:3]=1[C:13]([O:15][CH3:16])=[O:14]A mixture of methyl 7-amino-3-thioxo-3,4-dihydro-2H-benzo[1,4]oxazine-8-carboxylate (Intermediate 29, 0.795 g), methyl iodide (0.710 g) and potassium carbonate (1.38 g) in acetone (20 mL) was stirred at room temperature for 2 hours. The resultant mixture was filtered and the filtrate was concentrated in vacuo. The residue was purified by chromatography on silica, eluting with a mixture of ethyl acetate and cyclohexane with a gradient of 5-25% to give methyl 7-amino-3-methylsulfanyl-2H-benzo[1,4]oxazine-8-carboxylate (0.648 g) as a sandy coloured solid.
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