Methanol → 4,4-Difluoro-5-(2-fluoropyridin-3-yl)pyrrolidin-3-yl 4-methylbenzenesulfonate

To a solution of 4,4-difluoro-5-(2-fluoropyridin-3-yl)-3,4-dihydro-2H-pyrrol-3-yl 4-methylbenzenesulfonate (18.0 g) in tetrahydrofuran (180 mL) was added sodium borohydride (3.68 g) under ice-cooling, methanol (90 mL) was further added, and the mixture was stirred for 3 hr. The reaction mixture was concentrated under reduced pressure, and the residue was diluted with ethyl acetate and washed with water. The separated aqueous layer was extracted again with ethyl acetate. Combined organic layers were washed with saturated brine, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give 4,4-difluoro-5-(2-fluoropyridin-3-yl)pyrrolidin-3-yl 4-methylbenzenesulfonate. To a suspension of sodium hydride (9.74 g) in tetrahydrofuran (100 mL) was added dropwise a solution of 4,4-difluoro-5-(2-fluoropyridin-3-yl)pyrrolidin-3-yl 4-methylbenzenesulfonate in tetrahydrofuran (100 mL) under ice-cooling, 15-crown-5 (32.2 g) was added, and the mixture was stirred for 3 hr. Saturated aqueous ammonium chloride solution was added to the reaction mixture and concentrated under reduced pressure. The residue was diluted with ethyl acetate, and washed with 1 mol/L hydrochloric acid. The separated aqueous layer was extracted again with ethyl acetate. Combined organic layers were washed with saturated aqueous sodium hydrogen carbonate solution, water and saturated brine, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: hexane-ethyl acetate=9:1→3:1) to give the title compound as a colorless solid (yield 6.35 g, 72%).