Potassium Bromide → 3-{(S)-4-[(E)-3-(3-Chloro-4-fluoro-phenyl)-acryloyl]-3-methyl-2-oxo-piperazin-1-yl}-propionic acid

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Reaction Steps

Saturated aqueous sodium hydrogencarbonate solution (15 ml) was added to a solution of (S)-4-[(E)-3-(3-chloro-4-fluoro-phenyl)-acryloyl]-1-(3-hydroxy-propyl)-3-methyl-piperazin-2-one (PCT Int. Appl. WO 2009010429 A2; 5.70 g, 16.1 mmol), potassium bromide (191 mg, 1.61 mmol), and 2,2,6,6-tetramethylpiperidin-1-oxyl (25 mg, 0.16 mmol) in dichloromethane (300 mL). Sodium hypochlorite solution (10% in water, 9.6 ml, 16 mmol) was added portionwise at 0° C., and the course of the oxidation was monitored by thin layer chromatography. After all starting material had reacted, the reaction mixture was washed with sodium hydrogencarbonate, and the aqueous layer was extracted twice with dichloromethane. The organic phases were pooled, dried over magnesium sulfate, filtered, and evaporated, thus affording 3-{(S)-4-[(E)-3-(3-chloro-4-fluoro-phenyl)-acryloyl]-3-methyl-2-oxo-piperazin-1-yl}-propionaldehyde (5.15 g, 91%). The aqueous layer was acidified to pH 3 with 1 M aq. hydrochloric acid solution and extracted with dichloromethane. The organic layer was dried over magnesium sulfate, filtered, and evaporated to afford the title compound (254 mg, 4%). Colorless gum, MS: 367.3 (M−H, Cl)−.

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