Acetic Acid → 4-[(E)-3-(3,4-Dichloro-phenyl)-acryloyl]-3-methyl-1-(4-piperidin-1-yl-butyl)-piperazin-2-one

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Sodium metaperiodate (310 mg, 1.45 mmol) and osmium(VIII) oxide (2.5% solution in tert-butylalcohol, 49 μl, 48 μmol) were added at 0° C. to a solution of 4-[(E)-3-(3,4-dichloro-phenyl)-acryloyl]-3-methyl-1-pent-4-enyl-piperazin-2-one (intermediate 20; 184 mg, 0.48 mmol) in acetone/water 1:1 (10 ml). The reaction mixture was stirred at 0° C. for 30 min, then allowed to reach room temperature over 45 min, then partitioned between ethyl acetate and water. The organic layer was washed with brine, dried (MgSO4), and evaporated. The crude aldehyde intermediate [4-{-4-[(E)-3-(3,4-dichloro-phenyl)-acryloyl]-3-methyl-2-oxo-piperazin-1-yl}-butyraldehyde] and piperidine (33 mg, 0.39 mmol) were dissolved in 1,2-dichloroethane (1.5 ml), then a freshly prepared solution of pyridine borane complex (8 M in pyridine, 71 μl, 0.78 mmol) and acetic acid (69 mg, 1.16 mmol) in ethanol (1.5 ml) was added dropwise at room temperature. The reaction mixture was stirred overnight, then 25%. aq. ammonium hydroxide solution (0.16 ml) was added, and volatile material was removed by rotary evaporation. The residue was purified by chromatography (SiO2; CH2Cl2/MeOH/NH4OH 90:10:0.25) to afford the title compound (15 mg, 11%). Light yellow solid, MS (ISP)=452.1 (M+H)+.

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