Methanesulfonic acid, 1,1,1-trifluoro-, anhydride with B,B-dibutylborinic acid → (S)-4-benzyl-3-[(2S,3R)-3-hydroxy-2-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-propionyl]-oxazolidin-2-one

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In analogy to the procedures described in examples 11 a] to 11 c], 7-[2-(5-methyl-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophene-4-carbaldehyde was reacted with (S)-4-benzyl-3-methoxyacetyl-oxazolidin-2-one and nBu2BOTf to yield (S)-4-benzyl-3-[(2S,3R)-3-hydroxy-2-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-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)-3-hydroxy-2-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-propionyl]-oxazolidin-2-one with triethylsilane in trifluoroacetic acid then gave (S)-4-benzyl-3-(2(S)-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-propionyl)-oxazolidin-2-one. The (S)-4-benzyl-3-(2(S)-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-propionyl)-oxazolidin-2-one was subsequently saponified with 1N NaOH in THF to yield (S)-2-methoxy-3-{7-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-4-yl}-propionic acid as colorless solid.

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