[C:1]([O:5][C:6]([NH:8][C@H:9]1[CH2:13][C@@:12]([CH2:18][O:19][CH2:20][CH3:21])([C:14]([O:16]C)=[O:15])[CH:11]=[CH:10]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O.[OH-].[Li+]>O1CCCC1.CO.O>[C:1]([O:5][C:6]([NH:8][C@H:9]1[CH2:13][C@@:12]([CH2:18][O:19][CH2:20][CH3:21])([C:14]([OH:16])=[O:15])[CH:11]=[CH:10]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]To a solution of methyl (1R,4S)-4-[(tert-butoxycarbonyl)amino]-1-(ethoxymethyl)cyclopent-2-ene-1-carboxylate (3.25 g, 10.8 mmol) in tetrahydrofuran (58.7 mL), methanol (58.7 mL) and water (12.6 mL) was added lithium hydroxide monohydrate (0.731 g, 17.42 mmol). The pink mixture was heated to reflux overnight. The organic solvents were removed in vacuo and the aqueous layer was washed once with ether and then acidified slowly with concentrated HCl until the pH reached 4. The resulting suspension was extracted with methylene chloride three times. The combined organic layers were dried over MgSO4, filtered and concentrated to give the desired product as a mixture of cis/trans isomers (2.75 g, 89%). MS calculated for C14H24NO5: (M+H) 286.2; found 186.2 (M+H-Boc).
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