[C:1]([C:3]1[CH:4]=[C:5]([C:9]2[N:10]=[C:11]3[N:15]([CH:16]=2)[CH:14]=[CH:13][S:12]3)[CH:6]=[CH:7][CH:8]=1)#[N:2].[C:17](OC(=O)C)(=[O:19])[CH3:18].S(=O)(=O)(O)O>ClCCl>[C:1]([C:3]1[CH:4]=[C:5]([C:9]2[N:10]=[C:11]3[N:15]([C:16]=2[C:17](=[O:19])[CH3:18])[CH:14]=[CH:13][S:12]3)[CH:6]=[CH:7][CH:8]=1)#[N:2]To a mixture of 6-(3-cyanophenyl)-imidazo[2,1-b]thiazole (5.50 g, 24.4 mmol) and acetic anhydride (50 mL) was added 0.6 mL of concentrated sulfuric acid. The reaction mixture was heated at 135° C. for 5 hours. After cooling to room temperature, the reaction mixture was diluted with dichloromethane (100 mL), washed with water (50 mL×2), saturated aqueous sodium bicarbonate solution (50 mL×2), water (50 mL), dried over sodium sulfate, filtered and concentrated in vacuo. Product was purified by flash chromatography on silica gel eluting with 40% ethyl acetate in hexane to yield 4.8 g (74%) of the title compound as a light yellow solid. LCMS: 268 [M+H].
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