[CH2:1]([O:3][C:4]([C:6]1[C:7](=[O:14])[NH:8][N:9]2[CH:13]=[CH:12][S:11][C:10]=12)=[O:5])[CH3:2].C(=O)([O-])[O-].[Cs+].[Cs+].I[CH2:22][CH3:23]>CN(C=O)C>[CH2:1]([O:3][C:4]([C:6]1[C:7]([O:14][CH2:22][CH3:23])=[N:8][N:9]2[CH:13]=[CH:12][S:11][C:10]=12)=[O:5])[CH3:2]To a DMF (119 mL) solution of 6-oxo-5,6-dihydro-pyrazolo[5,1-b][1,3]thiazole-7-carboxylic acid ethyl ester (8.5 g, 40.2 mmol), cesium carbonate (26.1 g, 80.2 mmol) and iodoethane (8.3 mL, 80.2 mmol) were added while stirring at room temperature. The mixture was stirred at room temperature for one hour, was extracted with diethyl ether, washed with brine, and dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. The residue was purified by medium pressure amino silica gel column chromatography (n-heptane/ethyl acetate: 10% then 40%) to obtain the title compound (7.01 g, 29.2 mmol).
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