[C:1]([N:6]1[CH2:11][CH2:10][C:9](=[O:12])[CH2:8][CH2:7]1)([O:3][CH2:4][CH3:5])=[O:2].B(F)(F)F.[CH3:17]COCC.[N+]([C:27]([O:29][CH2:30][CH3:31])=[O:28])(C([O-])=O)=[N-]>CCOCC>[O:12]=[C:9]1[CH2:10][CH2:11][N:6]([C:1]([O:3][CH2:4][CH3:5])=[O:2])[CH2:17][CH2:7][CH:8]1[C:27]([O:29][CH2:30][CH3:31])=[O:28]To a cold solution (−30° C.) of 1-carbethoxypiperidin-4-one (3.0 ml, 26.5 mmol) in anhydrous ether, were simultaneously added a solution of boron trifluoride etherate (3.4 ml, 26.5 mmol) in diethyl ether (2.8 ml) and a solution of ethyl diazodicarboxylate (3.6 ml, 34.5 mmol) in diethyl ether (2.8 ml) over 1.5 hours via a syringe-pump. Upon completion of additions, the reaction mixture was allowed to stir for an additional hour at −30° C. and then warmed to room temperature. The reaction mixture was washed with 30% potassium carbonate and the organic phase was dried over Na2SO4 and concentrated in vacuo to give diethyl 5-oxoazepane-1,4-dicarboxylate as a crude yellow oil.
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