tert-Butylsulfinamide, (S)-(-)- → (S)-ethyl 2-(5-bromo-2-(methoxymethoxy)phenyl)-2-(tert-butylsulfinylimino)acetate

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A flask was charged with 2,4-dibromophenol (50.4 g, 200 mmol), potassium carbonate (69.1 g, 500 mmol) and acetone (500 mL). The suspension was stirred at RT for 30 minutes and then treated dropwise with chloromethyl ethyl ether (19 mL, 213 mmol). After 3 h at RT the mixture was filtered and the filtrate was partitioned between EtOAc and water. The organic phase was separated, washed with water, aqueous saturated NaHCO3 and brine. The organic phase was dried over MgSO4 and the solvent was removed under reduced pressure to afford 54.2 g 2,4-dibromo-1-(methoxymethoxy)benzene, which was used in the next step without further purification. Step 2: A solution of 2,4-dibromo-1-(methoxymethoxy)benzene (40.5 g, 137 mmol) in Et2O (140 mL) was cooled to −78° C. and treated with n-BuLi (2.5M in hexanes; 60.2 mL, 151 mmol) under nitrogen atmosphere. After 30 minutes a solution of diethyl oxalate (27.9 mL, 205 mmol) in Et2O (20 mL) was added dropwise. The reaction mixture was stirred for 45 minutes at that temperature then quenched cold with saturated ammonium chloride solution. The mixture was partitioned between Et2O and water. The organic phase was separated, washed with water, brine, then dried over MgSO4. The solvent was removed under reduced pressure to afford 49 g of ethyl 2-(5-bromo-2-(methoxymethoxy)phenyl)-2-oxoacetate, which was used in the next step without further purification. Step 3: A flask was charged with (S)-2-methylpropane-2-sulfinamide (0.764 g, 6.31 mmol) and neopentylzinc(II) iodide (0.5 M in THF, 10.0 mL, 5.00 mmol) was added under nitrogen atmosphere. The mixture was stirred at RT for 15 minutes and ethyl 2-(5-bromo-2-(methoxymethoxy)phenyl)-2-oxoacetate (1.00 g, 3.15 mmol) was added in one portion. The reaction mixture was quenched with saturated aqueous ammonium chloride after 8 h. The reaction was partitioned between EtOAc and water. The organic phase was separated, washed with NH4Cl, water and brine. The organic phase was dried over MgSO4 and the solvent was removed under reduced pressure. The crude material was purified by silica gel chromatography (10-30% EtOAc/hexane) to provide 0.675 g (S)-ethyl 2-(5-bromo-2-(methoxymethoxy)phenyl)-2-(tert-butylsulfinylimino)acetate.

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