A cooled (−78° C.) solution of 2-bromo-1-ethoxy-3-fluorobenzene (3.520 g; 16.10 mmol) in anh. THF (60 ml), under nitrogen, was treated dropwise with a solution of 1.6 M n-BuLi in hexanes (10.05 ml; 16.10 mmol). The resulting solution was further stirred at −78° C. for 5 min. A solution of ethyl 4-((tert-butylsulfinyl)imino)-2-methylbutanoate (2.650 g; 10.70 mmol) in anh. THF (20 ml) was then added dropwise to the cooled reaction mixture, and stirring at −78° C. was continued for 30 min. The resulting reaction mixture was treated successively with aq. sat. NH4Cl (75 ml), Et2O (250 ml) and water (75 ml). The separated organic layer was then washed with brine (75 ml), dried over anh. MgSO4, filtered, and concentrated to dryness under reduced pressure. Purification by FC (DCM/MeOH=30/1) afforded ethyl 4-(1,1-dimethylethylsulfinamido)-4-(2-ethoxy-6-fluorophenyl)-2-methylbutanoate as a yellow oil. LC-MS (conditions A): tR=0.85 min. and [M+H]+: 388.35 g/mol; tR=0.88 min. and [M+H]+: 388.37 g/mol (mixture of diastereoisomers).
