Diketene → HCID 86621302, compound

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Reaction Steps

2-{[4-(2-Aminoethyl)-1,3-thiazol-2-yl]thio}-2-methylpropionic acid tert-butyl ester (3.0 g) synthesized in Example 7 was dissolved in N,N-dimethylformamide (50 mL), and diketene (0.88 g) was added dropwise under ice-cooling. After raising to room temperature, the mixture was stirred for one hour. The mixture was diluted with ethyl acetate, and the organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to give 2-({4-[2-(acetoacetylamino)ethyl]-1,3-thiazol-2-yl}thio)-2-methylpropionic acid tert-butyl ester (3.4 g) as a colorless oil. This compound was used in the next step without particular purification. [4-(Trifluoromethoxy)phenyl]hydrazine hydrochloride (390 mg) was dissolved in ethanol (8 mL), pulverized sodium hydroxide (65 mg) was added at room temperature. The insoluble material was filtered through celite, and the solvent was evaporated under reduced pressure. The residue was dissolved again in ethanol (8 mL), 2-({4-[2-(acetoacetylamino)ethyl]-1,3-thiazol-2-yl}thio)-2-methylpropionic acid tert-butyl ester (600 mg) obtained earlier was added at room temperature, and the mixture was stirred for 30 min. The solvent was evaporated under reduced pressure, water was added, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure, and the residue was dissolved in tetrahydrofuran (8 mL), diphosphorus pentasulfide (345 mg) and sodium carbonate (329 mg) were added, and the mixture was heated under reflux for 2 hr. The solvent was evaporated, and the residue was purified by silica gel chromatography (elution solvent; hexane:ethyl acetate=4:1) to give the title compound (690 mg) as a colorless oil.

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