[O:1]=[C:2]1[CH2:6][CH2:5][CH2:4][NH:3]1.[Li]CCCC.C1COCC1.[C:17]1(=[O:23])[O:22][C:20](=[O:21])[CH2:19][CH2:18]1.Cl>C1COCC1>[O:23]=[C:17]([N:3]1[CH2:4][CH2:5][CH2:6][C:2]1=[O:1])[CH2:18][CH2:19][C:20]([OH:22])=[O:21]A solution of 2-oxopyrrolidine (5.00 g) in THF (60 ml) was cooled to -50° C., and a 1.55 M n-BuLi/THF solution (38 ml) was dropwise added thereto. After 0.5 hour's stirring at -30° C., succinic anhydride (6.00 g) was added dropwise, followed by stirring at a temperature of -30°--20° C. for 0.5 hour. The reaction mixture was poured into ice water and adjusted to pH 4 with 1N hydrochloric acid, and extracted with n-butanol. The organic layer was washed with saturated brine and concentrated to give 9.42 g of 4-oxo-4-(2-oxo-1-pyrrolidinyl)butyric acid.
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