Tetrahydrofuran → Ethyl 2-{[(2R)-2-[(tert-butylsulfinyl)amino]-2-(3,5-difluorophenyl)ethyl]thio}-2-methylpropanoate

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To methyl 2-{[2-(3,5-difluorophenyl)-2-oxoethyl]thio}-2-methylpropanoate from Step B (500. mg, 1.74 mmol) was added (R)-(+)-2-methyl-2-propanesulfinamide (254 mg, 2.09 mmol) under a constant stream of nitrogen. The reagents were dissolved in THF (17 mL), and to the above mixture was added titanium ethoxide (796 mg, 3.49 mmol). The reaction was sealed and stirred at 60° C. for 15 hours. The reaction was complete as determined by LCMS analysis and transesterification was observed. The reaction was cooled gradually to 0° C. under nitrogen. To the reaction mixture was added sodium borohydride (132 mg, 3.49 mmol). The reaction was complete after fifteen minutes as indicated by LCMS analysis. The reaction was quenched after an additional twenty minutes of stirring with methanol until gas evolution ceased. Saturated brine (30 mL) was added with heavy stirring and the resulting slurry was filtered through celite and washed with aliquots of ethyl acetate. The organic layer was then washed with brine and dried over sodium sulfate. The solution was filtered and concentrated in vacuo to provide a residue that was purified by silica gel chromatography, eluting with a gradient of EtOAc:Hexanes—20:80 to 75:25, to give the title compound (containing 10% of the undesired diastereomer). MS: m/z=408 (M+1).

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