sec-Butyl lithium (1.4 M in cyclohexane, 3.2 eq) was added to a stirred solution of (2R,6S)-4-[6-({[tert-butyl(diphenyl)silyl]oxy}methyl)-2,3-difluorophenyl]-2,6-dimethylmorpholine (Intermediate 3, 1.0 g, 2.02 mmol) in anhydrous THF (10 mL) at −78° C., and the mixture was stirred for 2 h. N-methoxy-N,2-dimethyl-1,3-oxazole-4-carboxamide (1.0 g, 6.46 mmol) in THF (5 mL) was added dropwise and stirring was continued for an additional 1 h. The reaction mixture was quenched with saturated ammonium chloride solution and extracted with ethyl acetate. The organic layer was washed with brine and dried over anhydrous sodium sulphate. The solvent was removed under vacuum and the residue was purified by silica gel chromatography using ethylacetate-pet. ether gradient to obtain product. Yield: 600 mg, (50%)
