[O:1]=[C:2]1[CH2:6][CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3]1.[CH3:14][N:15]([CH:17](OC)OC)[CH3:16]>>[CH3:14][N:15](/[CH:17]=[C:6]1/[CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3][C:2]/1=[O:1])[CH3:16]A solution of tert-butyl 3-oxopyrrolidine-1-carboxylate (40 g, 216 mmol) was treated with DMF-DMA (267 g, 2241 mmol) and heated at 105° C. for 40 min. The solution was cooled and evaporated under reduced pressure and the resulting orange solid was treated with hexane (200 mL) and cooled in the refrigerator over the weekend. The resulting brownish-yellow solid was collected by filtration, dried and used in the next setp without further purification.
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