A solution of (R)-3-[1-(3-bromo-phenyl)-1H-pyrazol-4-yl]-2,2-difluoro-3-((R)-2-methyl-propane-2-sulfinylamino)-butyric acid ethyl ester (700 mg, 2.42 mmol) in tetrahydrofuran (5 ml) was treated slowly with lithium borohydride (2M solution in tetrahydrofuran, 0.78 ml, 2.66 mmol) at 0° C., and the mixture was stirred at 25° C. for 2 hours. For the workup, acetic acid (0.26 ml, 4.5 mmol) was added slowly over a period of 15 minutes followed by water (2 ml), and the mixture was stirred for 30 minutes at 25° C. before it was quenched with a solution of sodium hydrogencarbonate (20 ml) and extracted with ethyl acetate (3×100 ml). The combined organic layers were washed with brine (75 ml), dried over sodium sulphate, and evaporated at reduced pressure. The crude material thus obtained was purified by column chromatography on silica gel using a gradient of hexane/ethyl acetate=85:15 to 80:20 as the eluent to give the (R)-2-methyl-propane-2-sulfinic {(R)-1-[1-(3-bromo-phenyl)-1H-pyrazol-4-yl]-2,2-difluoro-3-hydroxy-1-methyl-propyl}-amide (460 mg, 67% yield) as a deep brown solid. MS (ISP): m/z=450.2 [M+H]+.
