(Z)-2-Methoxy-3-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-7-yl}-acrylic Acid → Aleglitazar

Participants

Reaction Steps

In an analogous manner to Example 10, 2.5 g (5.74 mmol) of (Z)-2-methoxy-3-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-7-yl}-acrylic acid were asymmetrically hydrogenated in the presence of 3.22 mg of [Ru(OAc)2((S)-6-MeO-2-naphthyl)-MeOBIPHEP)] (S/C molar ratio 2000) at 40° C. under 15 bar of hydrogen for 24 h to reach 99.6% conversion. Rotary evaporation of the reaction mixture afforded quantitatively (S)-2-methoxy-3-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-7-yl}-propionic acid of 75.8% ee with 98.5% purity (HPLC area). To a solution of 6.50 g (15.8 mmol) of crude product in 33 ml of tetrahydrofuran was added dropwise at reflux (63-65%° C.) under stirring a solution of 1.91 g (15.6 mmol) of (S)-phenyl ethylamine (commercially available from Fluka) in 3 ml of tetrahydrofuran. Addition of seed crystals and turning off the bath heating brought about the start of the crystallization. The crystallization was completed over night at room temperature, the white crystals were filtered off, washed with 20 ml of cold (−20° C.) tetrahydrofuran and dried to constant weight (50° C./10 mbar/6h) to afford 6.57 g (79.2%) of (S)-2-methoxy-3-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzo[b]thiophen-7-yl}-propionic acid as (S)-phenyl ethylamine salt of 96.3% ee with 99.9% purity (HPLC area), with a mp. of 157-159.5° C.

Provenance & Evidence