Methanesulfonic acid, 1,1,1-trifluoro-, anhydride with B,B-dibutylborinic acid → (S)-4-benzyl-3-((2S,3R)-2-ethoxy-3-hydroxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionyl)-oxazolidin-2-one

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In analogy to the procedures described in examples 11 a] to 11 c], 3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzaldehyde (example 114 b]) was reacted with (S)-4-benzyl-3-ethoxyacetyl-oxazolidin-2-one and nBu2BOTf to yield (S)-4-benzyl-3-((2S,3R) -2-ethoxy-3-hydroxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionyl)-oxazolidin-2-one (according to NMR, one of the four isomers is strongly predominating; the configuration was tentatively assigned as 2S, 3R according to Tetrahedron Asymmetry 1999, 1353). Reduction of (S)-4-benzyl-3-((2S,3R)-2-ethoxy-3-hydroxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionyl)-oxazolidin-2-one with triethylsilane in trifluoroacetic acid then gave (S)-4-benzyl-3-((2S)-2-ethoxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionyl)-oxazolidin-2-one. The (S)-4-benzyl-3-((2S)-2-ethoxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionyl)-oxazolidin-2-one was subsequently saponified with 1N NaOH in THF to yield (S)-2-ethoxy-3-{3-methyl-4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionic acid as colorless solid. The enantiomeric excess was judged according to chiral HPLC (Chiralpak-AD) to be 99.3%.

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