[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH2:11][CH2:10][C:9]1=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].[F:15][C:16]1[CH:30]=[CH:29][C:19]([CH2:20]P(=O)(OCC)OCC)=[CH:18][CH:17]=1.[H-].[Na+].C(=O)(O)[O-].[Na+]>O1CCCC1.C1OCCOCCOCCOCCOC1>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][C:11](=[CH:20][C:19]2[CH:29]=[CH:30][C:16]([F:15])=[CH:17][CH:18]=2)[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]A solution of 59.78 g of N-t-butoxycarbonylpiperidone and 81.25 g of diethyl 4-fluorobenzylphosphonate in 150 ml of tetrahydrofuran was added dropwise to a suspension of 13.20 g of 60% sodium hydride (in oil) containing 1.65 g of 15-crown-5 ether in 650 ml of tetrahydrofuran which was cooled in an ice bath over 20 minutes. After 1 day of stirring at room temperature, saturated aqueous sodium bicarbonate was carefully added to the reaction mixture which was subsequently extracted with ethyl acetate. The extract was washed with saturated aqueous sodium bicarbonate and saturated brine and dried over anhydrous sodium sulfate, the drying agent was removed by filtration, and then the resulting filtrate was concentrated under reduced pressure and purified by a flash column chromatography (silica gel: Wako Gel C200 (manufactured by Wako Pure Chemical Industries), eluant: hexane-ethyl acetate=20.1) to obtain 55.23 g of N-t-butoxycarbonyl-4-(4-fluorobenzylidene)piperidine. The thus obtained oily product was crystallized after its overnight standing at room temperature.
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