[Cl:1][C:2]1[CH:3]=[C:4]([CH3:18])[C:5]2[O:9][C:8]([N:10]3[CH2:16][CH2:15][CH2:14][NH:13][CH2:12][CH2:11]3)=[N:7][C:6]=2[CH:17]=1.[S:19](=[O:23])(=[O:22])([OH:21])[OH:20].CO.CO.S(=O)(=O)(O)O>C(OCC)(=O)C>[S:19]([OH:23])([OH:22])(=[O:21])=[O:20].[Cl:1][C:2]1[CH:3]=[C:4]([CH3:18])[C:5]2[O:9][C:8]([N:10]3[CH2:16][CH2:15][CH2:14][NH:13][CH2:12][CH2:11]3)=[N:7][C:6]=2[CH:17]=1A solution of 5-chloro-2-(1-homopiperazinyl)-7-methylbenzoxazole (2.5 g) in ethyl acetate (75 mL) was added dropwise with a separately prepared sulfuric acid/methanol solution [prepared by adding methanol to 95% sulfuric acid (0.53 mL) to a total volume of 12.5 mL] at room temperature with stirring. The mixture was stirred for 1 hour with ice cooling, and the produced colorless precipitates were collected by filtration. The precipitates were dried at 35 C.° under reduced pressure for 5 hours to obtain the title compound (3.3 g).
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