Hydrochloric Acid → (2R,4S)-Methyl 2-(3,4-difluorobenzyl)-4-(3-oxo-2,3-dihydroisoxazol-5-yl)piperidine-1-carboxylate

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Reaction Conditions

Reaction Steps

Cis-methyl 2-(3,4-difluorobenzyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate (2.233 g, 5.82 mmol) was dissolved in MeOH (20 mL) and cooled to −40° C. under nitrogen. Sodium hydroxide (0.233 g, 5.82 mmol) dissolved in water (2.000 mL) was added during 10 min and the yellow solution continued to stir at −40° C. for 20 min. Hydroxylamine (50% by weight in water, 0.357 mL, 5.82 mmol) was added during 8 min. The resulting solution was stirred at −40° C. for 3 h. The mixture was then rapidly poured into a prewarmed (80° C.) solution of 6 M hydrogen chloride (30 mL, 180.00 mmol) and the mixture continued to stir at 80° C. for 20 min. The solvent was evaporated and DCM/water added. The phases were separated and the organic phase passed through a phase separator and evaporated to yield a yellow semi-solid. The compound was purified by preparative HPLC in 3 injections on a XBridge C18 column (10 μm 250×50 ID mm) using a gradient of 0-25% Acetonitrile in H2O/MeCN/NH3 95/5/0.2 buffer over 20 minutes with a flow of 100 mL/min. Cis-methyl 2-(3,4-difluorobenzyl)-4-(3-oxo-2,3-dihydroisoxazol-5-yl)piperidine-1-carboxylate (1.361 g, 66%) was isolated as a white solid. 1H NMR (400 MHz, cdcl3) δ 1.84-2.14 (m, 4H), 2.52-2.62 (m, 1H), 2.71-2.80 (m, 1H), 2.95-3.05 (m, 1H), 3.09-3.20 (m, 1H), 3.64 (s, 3H), 3.95-4.06 (m, 1H), 4.20-4.30 (m, 1H), 5.74 (s, 1H), 6.77-6.83 (m, 1H), 6.90-6.98 (m, 1H), 6.98-7.09 (m, 1H). MS m/z 353 (M+H)+

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