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0 °C

To a 25 mL round-bottomed flask was added (R,E)-N-(1-(6-bromo-3-fluoro-4-(triethylsilyl)pyridin-2-yl)-2,2-difluoroethylidene)-2-methylpropane-2-sulfinamide (0.48 g, 1.018 mmol) and THF (4 mL). The mixture was cooled to 0° C. and 2-tert-butoxy-2-oxoethylzinc chloride 0.5 m in diethyl ether (5.09 mL, 2.55 mmol) was added dropwise over 10 min. After the addition the reaction mixture was stirred at 0° C. to rt for 4 h. The reaction mixture was diluted with sat NaHCO3 (50 mL) and extracted with EtOAc (3×50 mL). The combined extracts were washed with brine, dried (Na2SO4) and concentrated. The crude material was purified by chromatography through a Redi-Sep pre-packed silica gel column (40 g), eluting with a gradient of 0% to 20% EtOAc in hexane, to provide a 4:1 mixture of (R)-tert-butyl 3-(6-bromo-3-fluoro-4-(triethylsilyl)pyridin-2-yl)-3-((R)-1,1-dimethylethylsulfinamido)-4,4-difluorobutanoate and (5)-tert-butyl 3-(6-bromo-3-fluoro-4-(triethylsilyl)pyridin-2-yl)-3-((R)-1,1-dimethylethylsulfinamido)-4,4-difluorobutanoate (0.428 g, 0.728 mmol, 71.5% yield) as light-yellow oil. MS m/z=587, 589 M+, Calculated for C23H38BrF3N2O3SSi: 587.61. Used directly in the following step.

1. additionAfter the addition the reaction mixture
2. extractionextracted with EtOAc (3×50 mL)
3. washThe combined extracts were washed with brine
4. dry with materialdried (Na2SO4)
5. concentrationconcentrated
6. customThe crude material was purified by chromatography through a Redi-Sep pre-packed silica gel column (40 g)
7. washeluting with a gradient of 0% to 20% EtOAc in hexane
8. customto provide