[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH:11]([CH:14]=[O:15])[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH3:16][Mg]Br>O1CCCC1>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][CH:11]([CH:14]([OH:15])[CH3:16])[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]To a solution of N-tert-butoxycarbonyl-4-piperidinecarboxaldehyde (32.20 g, 151.45 mmol) in tetrahydrofuran at −78° C. is added methyl magnesium bromide (2 M in diethyl ether, 100.96 mL, 302.89 mmol). The reaction is stirred at −78° C. for 4.5 h, and then warmed to −50° C. for 30 min. The reaction is quenched with water at −50° C. and allowed to warm to room temperature for 16 h. The solvents are removed and the material is partitioned between diethyl ether and 0.1 M hydrochloric acid. The mixture is extracted with diethyl ether. The combined organic layers are washed with 0.1 M hydrochloric acid, saturated aqueous sodium bicarbonate and brine, dried over magnesium sulfate, filtered, and concentrated to dryness. The crude is purified by flash chromatography over silica gel to afford 16.90 g of the title compound as a colourless oil. MS (m/z) 229 (M+1).
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