Methanol → Methyl 2-(4-chlorophenyl)-3-methylbutyrate

Participants

Reaction Steps

Preparation of (2R)-3-methyl-2-[4(trifluoromethylsllfonyloxy)phenyl]butanoic acid. To a solution of commercial 2-(4-chlorophenyl)-3-methylbutyric acid (1 g, 4.7 mmol) in CH3OH (10 mL), few drops of conc. H2SO4 were added, and the resulting mixture was left stirring at room temperature overnight. After solvent evaporation under vacuum, CH2Cl2 (10 mL) and H2O (10 mL) were added; the two phases were separated and the organic one dried over Na2SO4, filtered and evaporated under vacuum to give the intermediate methyl 2-(4-chlorophenyl)-3-methylbutanoate as an oily residue (quantitative yield). This intermediate was transformed in the related methyl 2-(4-hydroxyphenyl)-3-methylbutanoate according a known procedure3: a mixture of methyl 2-(4-chlorophenyl)-3-methylbutanoate (1.06 g, 4.7 mmol), 60% sodium hydride (0.56 g, 14.1 mmol) and H2O (85 μL, 4.7 mmol) was heated to 45° C. while kept at argon atmosphere for 3 days (1H-NMR analysis). The solvent was evaporated and the residue diluted with EtOAc and washed with 1N HCl (2×5 mL); the solvent was evaporated under vacuum and the crude residue was purified by flash chromatography (CHCl3/CH3OH 85:15) to give the pure intermediate as an oil (0.75 g, 77% yield). 1H-NMR (CDCl3) δ 7.18 (d, 2H, J=7 Hz), 6.82 (d, 2H, J=7 Hz), 5.75 (bs, 1H, OH), 3.70 (s, 3H), 3.15 (d, 1H, J=14 Hz), 2.55 (m, 1H), 1.10 (d, 3H, J=7 Hz), 0.72 (d, 3H, J=7 Hz). The steps of insertion of the triflate group and the following hydrolysis were performed as described1 and 3-methyl-2-[4-(trifluoromethylsulfonyloxy)phenyl]butanoic acid was obtained as a colourless oil (0.91 g, 78% yield calculated from the 4-hydroxy methyl ester derivative). The optical resolution was performed as described.4 (2R)-3-methyl-2-[4-(trifluoromethylsulfonyloxy)phenyl]butanoic acid (0.32 g, 35% yield) was obtained as a white solid. [α]D25 (c=1, CH3OH): −50°; 1H-NMR (CDCl3) δ 7.55 (d, 2H, J=7 Hz), 7.25 (d, 2H, J=7 Hz), 3.15 (d, 1H, J=14 Hz), 2.55 (m, 1H), 1.10 (d, 3H, J=7 Hz), 0.72 (d, 3H, J=7 Hz).

Provenance & Evidence