Cis-methyl 4-(3-ethoxy-3-oxopropanoyl)-2-(4-fluorophenethyl)piperidine-1-carboxylate (3.15 g, 8.30 mmol) was dissolved in MeOH (30 mL) and cooled to −40° C. under nitrogen. Sodium hydroxide (0.332 g, 8.30 mmol) dissolved in water (3.00 mL) was added and the mixture was stirred at −40° C. for 15 min. Hydroxylamine (50% by weight in water, 0.509 mL, 8.30 mmol) was added. The resulting solution was stirred at −40° C. for 3 h. The mixture was then transferred into a prewarmed (80° C.) solution of 6 M hydrogen chloride (42.9 mL, 257.36 mmol) and the mixture was stirred at 80° C. for 20 min. DCM and water were added. The phases were separated and the organic phase passed through a phase separator and evaporated. The compound (split into 4 runs) 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. Cis-methyl 2-(4-fluorophenethyl)-4-(3-oxo-2,3-dihydroisoxazol-5-yl)piperidine-1-carboxylate (1.9 g, 66%) was isolated. 1H NMR (400 MHz, cdcl3) δ 1.53-2.14 (m, 6H), 2.46-2.64 (m, 2H), 2.98-3.07 (m, 1H), 3.12-3.24 (m, 1H), 3.70 (s, 3H), 3.87-3.99 (m, 1H), 4.05-4.16 (m, 1H), 5.72 (s, 1H), 6.85-6.94 (m, 2H), 7.04-7.11 (m, 2H). MS m/z 349 (M+H)+
