Hydrochloric Acid → cis-Methyl 2-(3,5-difluoro-4-(trifluoromethyl)phenyl)-4-(3-ethoxy-3-oxopropanoyl)-piperidine-1-carboxylate

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Reaction Steps

2-(3,5-Difluoro-4-(trifluoromethyl)phenyl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (2.363 g, 6.43 mmol) (reference compound 30) was dissolved in methyl THF (30 mL) and di(1H-imidazol-1-yl)methanone (1.565 g, 9.65 mmol) added. The suspension was stirred at room temperature under nitrogen for 20 h (flask 1). In a separate flask potassium 3-ethoxy-3-oxopropanoate (2.190 g, 12.87 mmol) and magnesium chloride (1.225 g, 12.87 mmol) were suspended in methyl THF (30.0 mL) and stirred with an oversized stirring bar at 50° C. under nitrogen for 20 h (flask 2). The white suspension in flask 2 was then added to flask 1. The thick white suspension was stirred at room temperature for 24 h. The reaction mixture was acidified by addition of 3 M HCl to pH 1. MTBE (250 mL) and water were added, shaken and the phases separated. The organic phase was washed with water (200 mL), satd NaHCO3 (200 mL), brine (200 mL), dried with a phase separator and evaporated in vacuo. The residue was purified by automated flash chromatography on a Biotage® KP-SIL 100 g column. A gradient from 40% EtOAc in heptane over 2 CV followed by 40% to 80% of EtOAc in heptane over 10 CV was used as mobile phase. Cis-methyl 2-(3,5-difluoro-4-(trifluoromethyl)phenyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate (1.489 g, 52.9%) and trans-methyl 2-(3,5-difluoro-4-(trifluoromethyl)phenyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate (0.110 g, 3.91%) were isolated. Cis-isomer: 1H NMR (600 MHz, cdcl3) δ 1.25 (t, 3H), 1.49-2.28 (m, 4H), 2.80-2.91 (m, 1H), 3.23-3.31 (m, 1H), 3.44 (s, 2H), 3.65 (s, 3H), 4.07-4.14 (m, 1H), 4.17 (q, 2H), 4.86-4.95 (m, 1H), 6.83 (d, 2H). Trans-isomer: 1H NMR (600 MHz, cdcl3) δ 1.24 (t, 3H), 1.54-1.60 (m, 1H), 1.73-1.89 (m, 1H), 1.96-2.03 (m, 1H), 2.38-2.47 (m, 1H), 2.53-2.62 (m, 1H), 2.76-2.84 (m, 1H), 3.40-3.49 (m, 2H), 3.75 (s, 3H), 4.17 (q, 2H), 4.15-4.42 (m, 1H), 5.40-5.71 (m, 1H), 6.87 (d, 2H).

Provenance & Evidence