[C:1]([N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[C:11]([NH:18]C(=O)C(C)(C)C)[C:12]=2[C:14]([O:16][CH3:17])=[O:15])[C@H:7]2[CH2:25][CH2:26][O:27][C@H:6]2[CH2:5]1)(=[O:3])[CH3:2]>S(=O)(=O)(O)O.CO>[C:1]([N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[C:11]([NH2:18])[C:12]=2[C:14]([O:16][CH3:17])=[O:15])[C@H:7]2[CH2:25][CH2:26][O:27][C@H:6]2[CH2:5]1)(=[O:3])[CH3:2]Concentrated sulfuric acid (5 drops) was added to a solution of methyl cis-(3aRS,9bRS)-5-acetyl-7-(2,2-dimethylpropionylamino)-1,2,3a,4,5,9b-hexahydro-furo[2,3-c]quinoline-6-carboxylate (Intermediate 30, 0.15 g) in methanol (5 mL) and the solution was stirred and heated at reflux for 48 hours. After cooling, the mixture was evaporated to low volume and the residue was dissolved in ethyl acetate and carefully washed with saturated aqueous sodium bicarbonate solution. The organic layer was filtered through a phase separator and the filtrate was evaporated to dryness to give methyl cis-(3aRS,9bRS)-5-acetyl-7-amino-1,2,3a,4,5,9b-hexahydrofuro[2,3-c]quinoline-6-carboxylate (0.09 g) as a brown gum.
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