To a solution (300 mL) of methyl 2-amino-5-cyclopropylthiophene-3-carboxylate (4.7 g) in methylene chloride were added triphosgene (3.06 g) and triethylamine (8.6 mL), and the mixture was stirred at room temperature for 2 hr. To the reaction mixture was added 1-(2,4-dimethoxyphenyl)methanamine (7.2 mL), and the mixture was further stirred at room temperature for 1 hr. The reaction mixture was washed with water and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The obtained residue was dissolved in methanol (300 mL), sodium methoxide (6.4 g) was added, and the mixture was stirred at 60° C. for 2 hr. The reaction mixture was concentrated under reduced pressure, and the obtained residue was extracted with 1N hydrochloric acid and chloroform. The chloroform layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The precipitated solid was collected by filtration to give the title compound as a colorless solid (8.53 g, 100%).
