(1) Platinum oxide (100 mg) was added to a solution of 5-hydroxyisoquinoline (2.9 g, 20 mmol) in acetic acid (30 mL) and the hydrogenation reaction was carried out at room temperature and atmospheric pressure. Upon completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated under reduced pressure. The residue was crystallized by toluene (20 mL) and collected by filtration. The resulting crystals were dissolved in a solvent mixture of 1 N aqueous sodium hydroxide (40 mL) and tetrahydrofuran (40 mL), followed by addition of di-tert-butyl dicarbonate (4.8 g, 22 mmol). The reaction mixture was stirred at room temperature for 1 h, after which 1 N hydrochloric acid (40 mL) was added. Extraction was carried out with ether, the extract was dried over anhydrous magnesium sulfate and the solvent was removed by evaporation under reduced pressure. The precipitated crystals were recrystallized by diisopropyl ether to give colorless crystals of 2-tert-butoxycarbonyl-5-hydroxy-tetrahydroisoquinoline (2.9 g, 58% yield). Melting point: 163-164 °C. 1H-NMR (CDCl3) δ: 1.49 (9H, s), 2.76 (2H, t, J = 6.0 Hz).
