[OH-].[Li+].[CH3:3][O:4][C:5]1[CH:6]=[C:7]2[C:12](=[CH:13][CH:14]=1)[CH:11]([C:15]([O:17]CC)=[O:16])[N:10]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[CH2:9][CH2:8]2.CCO.Cl>O.C1COCC1>[C:23]([O:22][C:20]([N:10]1[CH2:9][CH2:8][C:7]2[C:12](=[CH:13][CH:14]=[C:5]([O:4][CH3:3])[CH:6]=2)[CH:11]1[C:15]([OH:17])=[O:16])=[O:21])([CH3:26])([CH3:24])[CH3:25]2N Aqueous lithium hydroxide solution (73.6 mL, 147.23 mmol) was added to a solution of 1-ethyl 2-tert-butyl 6-methoxy-3,4-dihydroisoquinoline-1,2(1H)-dicarboxylate (8.23 g, 24.54 mmol) in a mixed solvent of EtOH (35 mL) and THF (35 mL) at room temperature, and the mixture was stirred for 2 hr. To the reaction mixture was added water, the pH of the mixture was adjusted to 3 with 2N hydrochloric acid, and the mixture was extracted with ethyl acetate (×3). The organic layer was washed with brine, and dried over magnesium sulfate, and the solvent was evaporated under reduced pressure to give 2-(tert-butoxycarbonyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid (7.59 g, 24.70 mmol, quant.) as a colorless oil.
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