Diisopropylethylamine → (S)-4-Benzyl-3-((2S,3R)-3-{2-[dimethyl-(1,1,2-trimethyl-propyl)-silanyloxy]-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-3-hydroxy-2-methoxy-propionyl)-oxazolidin-2-one

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1.8 g (7.21 mmol) (S)-4-Benzyl-3-methoxyacetyl-oxazolidin-2-one (for the preparation of (S)-4-benzyl-3-methoxyacetyl-oxazolidin-2-one see: D. Hunziker, N. Wu, K. Kenoshita, D. E. Cane, C. Khosla, Tetrahedron Lett. 1999, 40, 635-638) were dissolved under an argon atmosphere in 10 ml CH2Cl2 and treated with 1.44 ml (8.42 mmol) Hünig's base. After cooling to −78° C., nBu2BOTf was added slowly (7.21 ml of 1M solution in CH2Cl2) and enolborinate formation allowed to proceed for 0.25 hours at −78° C. and for 1 hour at 0° C. After recooling to −78° C., a solution of 2.8 g (6 mmol) of 2-[dimethyl-(1,1,2-trimethyl-propyl)-silanyloxy]-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzaldehyde in 10 ml CH2Cl2 was added via dropping funnel during 90 minutes and the mixture kept for 95 minutes at −78° C. and for one hour at 0° C. Pouring onto crashed ice, twofold extraction with AcOEt, washing with brine and water, drying over magnesium sulfate, and evaporation of the solvents, followed by chromatography (silica gel, heptane/AcOEt) left finally 2.905 g (67%) of the title compound as a yellow oil. According to 1H-NMR spectroscopy, one of the four isomers is strongly predominating. The configuration was tentatively assigned as 2S,3R according to D. Haigh et al., Tetrahedron: Asymmetry 1999, 10, 1353-1367.

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