Sodium hydride (1.265 g, 31.6 mmol) was added to a suspension of 6-fluoro-3-methyl-7-(methyloxy)-2-[3-(trifluoromethyl)phenyl]-4-quinolinecarboxylic acid (8.0 g, 21.09 mmol) in dimethyl sulfoxide (50 mL), and the mixture was stirred for 20 min. Sodium 2-propanethiolate (2.53 g, 23.20 mmol) was added, and the resulting mixture was stirred at 100° C. overnight. The mixture was cooled to room temperature, treated with NaH (1.27 g of 60% dispersion in mineral oil, 31.6 mmol) and sodium 2-propanethiolate (2.53 g, 23.20 mmol), and heated at 100° C. for an additional 4 hours. The reaction mixture was cooled to room temperature. Iodomethane (3.96 mL, 63.3 mmol) was added, and the mixture was stirred for 2 hours. The mixture was diluted with water and extracted with methylene chloride (three times). The combined organic extracts were washed with brine, dried over Na2SO4, filtered, and concentrated in vacuo. The residue was purified via column chromatography (ISCO, 330 g silica, 0-10% ethyl acetate/methylene chloride) to afford methyl 3-methyl-6-[(1-methylethyl)thio]-7-(methyloxy)-2-[3-(trifluoromethyl)phenyl]-4-quinolinecarboxylate (5.5 g, 58% yield). This material was used in the next step without further purification. MS (m/z) 450.1 (M+H+).
