Under a nitrogen atmosphere, a solution of methyl 4-fluoro-5-phenyl-1-(pyridin-3-ylsulfonyl)-1H-pyrrole-3-carboxylate (200 mg) in tetrahydrofuran (10 mL) was cooled to −78° C., and a 1.5 mol/L solution (1.85 mL) of diisobutylaluminum hydride in toluene was added with stirring. After stirring at the same temperature for 15 min, the mixture was raised to 0° C. over 1.5 hr. Water (20 mL) was added, and the mixture was stirred at the same temperature for 5 min. After stirring, ethyl acetate (20 mL) was added, and the mixture was stirred for 15 min, and then stirred at room temperature for 20 min. The reaction mixture was filtered through celite, and celite was washed with ethyl acetate. The filtrate was extracted with ethyl acetate. The extract was washed with saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The residue was dissolved in tetrahydrofuran (10 mL), manganese dioxide (75% chemically treated product, 1.0 g) was added, and the mixture was stirred at room temperature for 16 hr. The reaction mixture was filtered through celite, and celite was washed with ethyl acetate. The filtrate was concentrated under reduced pressure and the residue was purified by silica gel column chromatography (eluent:hexane-ethyl acetate=19:1→1:2) to give the title compound as a colorless solid (yield 123 mg, 67%).
