To a solution of (S)-2-(tert-butyldiphenylsilyloxy)propanoic acid (0.70 g, 2.14 mmol) in DMF (20 mL) was added 5-(2,5-difluorophenyl)-2-((methoxymethoxy)methyl)-2-phenyl-2,3-dihydro-1,3,4-thiadiazole (0.50 g, 1.43 mmol) followed by PyBOP (1.11 g, 2.14 mmol) and DIEA (497 μL, 2.85 mmol). After stirring at room temperature for 16 hours, the mixture was treated with saturated NaHCO3 (50 mL) and extracted with ethyl acetate (3×30 mL). The combined organics were washed with water (6×30 mL) and brine (30 mL), dried over Na2SO4, and concentrated under reduced pressure. The yellow residue was chromatographed (19:1 to 9:1 hexanes/ethyl acetate) to afford the less polar diastereomer (S)-2-(tert-butyldiphenylsilyloxy)-1-((R)-5-(2,5-difluorophenyl)-2-((methoxymethoxy)methyl)-2-phenyl-1,3,4-thiadiazol-3(2H)-yl)propan-1-one (110 mg, 12%), and the more polar diastereomer (S)-2-(tert-butyldiphenylsilyloxy)-1-((S)-5-(2,5-difluorophenyl)-2-((methoxy-methoxy)methyl)-2-phenyl-1,3,4-thiadiazol-3(2H)-yl)propan-1-one (146 mg of a 1:1 mixture with starting material) as yellow oils. Absolute stereochemistry was assigned by inference from (S)-1-((R)-5-(2,5-difluorophenyl)-2-(hydroxymethyl)-2-phenyl-1,3,4-thiadiazol-3(2H)-yl)-2-methoxypropan-1-one.
