Tetrafluoroboric acid (1.5 ml) and an aqueous sodium nitrite solution (20 mg/0.2 ml, 0.29 mmol) were added, at 0° C., to a dioxane (2 ml) solution of (2S)-2-[(2aminophenyl)amino]-1-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)-3,3dimethylbutan-1-one (100 mg, 0.25 mmol) obtained in Example 25, and the mixture was stirred at that temperature for 30 minutes. Copper (I) oxide (75 mg, 0.52 mmol) was added to the reaction solution, and the mixture was stirred for 30 minutes. Dioxane (2 ml) and water (10 ml) were added to the mixture, and the mixture was concentrated under reduced pressure. The residue was extracted twice with chloroform (each 5 ml), and the extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was purified by silica gel thin layer chromatography using hexane and ethyl acetate (2:1) as an eluent to obtain the captioned compound (68.0 mg, 70%) as a green oily substance.
