A suspension of activated zinc (1.7 g, 26.6 mmol) and CuCl (269 mg, 2.72 mmol) in dry tetrahydrofuran (15 ml) was refluxed for 30 minutes under vigorous stirring. A solution of bromo-difluoroacetic acid methylester (0.87 ml, 6.79 mmol) in tetrahydrofuran (5 ml) was added dropwise at 25° C. and the mixture was stirred for 30 minutes. Thereafter, a solution of (R)-2-methyl-propane-2-sulfinic acid [1-[1-(3-bromo-phenyl)-1H pyrazol-4-yl]-eth-(E)-ylidene]-amide (1.0 g, 2.72 mmol) in tetrahydrofuran (5 ml) was added dropwise at 25° C., and stirring continued for 30 minutes. For the workup, ethanol (0.3 ml, 4.89 mmol) was added to the reaction mixture at 25° C., and the resultant mixture was filtered over a layer of Celite®. The filtrate was diluted with water (20 ml), and extracted with ethyl acetate (5×30 ml). The combined organic layers were washed with brine (50 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=60:40 to 50:50 as the eluent to give the (R)-3-[1-(3-bromo-phenyl)-1H-pyrazol-4-yl]-2,2-difluoro-3-((R)-2-methyl-propane-2-sulfinylamino)-butyric acid ethyl ester (600 mg, 45% yield) as a yellow solid. MS (ISP): m/z=490.0 [M+H]+.
