Hydrochloric Acid → trans-Methyl 2-(3-fluorobenzyl)-4-(3-oxo-2,3-dihydroisoxazol-5-yl)piperidine-1-carboxylate

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Reaction Conditions

Reaction Steps

Trans-methyl 4-(3-ethoxy-3-oxopropanoyl)-2-(3-fluorobenzyl)piperidine-1-carboxylate (0.663 g, 1.81 mmol) (from example 99, step 1) was dissolved in MeOH (8 mL) and cooled to −40° C. under nitrogen. Sodium hydroxide (0.073 g, 1.81 mmol) dissolved in water (1 mL) was added during 20 min and the yellow solution continued to stir at −40° C. for 20 min. Hydroxylamine (50% by weight in water, 0.111 mL, 1.81 mmol) was added during 5 min. The resulting solution was stirred at −40° C. for 4 h. The mixture was then rapidly poured into a prewarmed (80° C.) solution of 6 M hydrogen chloride (9 mL, 54.00 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 brown semi-solid. The compound was purified by preparative HPLC 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. Trans-methyl 2-(3-fluorobenzyl)-4-(3-oxo-2,3-dihydroisoxazol-5-yl)piperidine-1-carboxylate (214 mg, 35%) was isolated. 1H NMR (400 MHz, cdcl3) δ 1.47-1.77 (m, 2H), 1.82-2.15 (m, 2H), 2.75-3.00 (m, 2H), 3.00-3.15 (m, 2H), 3.40-3.80 (m, 3H), 4.00-4.42 (m, 1H), 4.42-4.80 (m, 1H), 5.64 (s, 1H), 6.83-7.05 (m, 3H), 7.22-7.31 (m, 1H). MS m/z 335 (M+H)+

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