Isobutyraldehyde → (2S,3S)-2-((4R)-2-benzhydryl-4-phenyl-oxazolidin-3-yl)-3-hydroxy-4-methyl-pentanoic acid tert-butyl ester

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A solution of tert-butyl ((4R)-2-benzhydryl-4-phenyl-oxazolidin-3-yl)-acetate (3.0 g, 6.98 mmole, obtained from Reference Example 10) in anhydrous terahydrofuran (86 ml) was cooled at −78° C. under argon. A solution of lithium diisopropylamide (2M solution in heptane/tetrahydrofuran/ethylbenzene, Aldrich) was added dropwise over a period of 10 min, and the resulting orange solution was stirred at −78° C. for 1 h. A solution of isobutyraldehyde in anhydrous tetrahydrofuran (10 ml) was added to the cooled reaction mixture via syringe, and the resulting mixture was stirred at −78° C. for an additional 1 h. Saturated sodium bicarbonate aqueous solution was added, and the mixture was warmed to room temperature. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (3 times). The extracts were combined, washed with saturated sodium chloride aqueous solution, dried over magnesium sulfate, filtered and concentrated. The residue was chromatographed (flash column, silica gel, methylene chloride:methanol:diethyl ether=90:2:8) to give (2S,3S)-2-((4R)-2-benzhydryl-4-phenyl-oxazolidin-3-yl)-3-hydroxy-4-methyl-pentanoic acid tert-butyl ester (1.5 g, %) as a pale yellow solid.

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