[CH3:1][CH:2]1[CH2:7][C:6](=[O:8])[CH2:5][C:4](=O)[CH2:3]1.CC([O-])=O.[Na+].BrBr.[NH2:17][C:18]([NH2:20])=[S:19]>CC(O)=O>[NH2:20][C:18]1[S:19][C:5]2[C:6](=[O:8])[CH2:7][CH:2]([CH3:1])[CH2:3][C:4]=2[N:17]=15-Methyl-cyclohexane-1,3-dione (70.0 g, 0.555 mol) and NaOAc (68.3 g, 0.832 mol) are suspended in AcOH (700 mL) and Br2 (88.7 g, 0.555 mol) is added drop-wise while maintaining the reaction temperature between 15 and 20° C. After complete addition, the reaction is stirred at RT overnight. Thiourea (42.2 g, 0.555 mol) is added in portions and the reaction mixture is heated to 100° C. for 1 h. After cooling to RT, the AcOH is removed in vacuo. The resulting crude product is diluted with water (1 L), adjusted to pH=7 with NaHCO3 solution (3 M) and the resulting mixture is extracted with EtOAc (3×1 L). The organic phase is washed with brine and dried over anhydrous Na2SO4. The solvent is evaporated in vacuo and the residue is recrystallized from hexane to give 2-amino-5-methyl-5,6-dihydro-4H-benzothiazol-7-one (87.2 g, 86% yield).
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