To a 1,4-dioxane (100 mL) solution of 5-amino-1,2,3,4-tetrahydroisoquinoline (3.68 g, 24.8 mmol) was added an aqueous 3 N NaOH solution (8.27 mL, 24.8 mmol). After the reaction mixture was cooled to 0°C, a solution of 1,4-dioxane (10 mL) in di-tert-butyl dicarbonate (5.42 g, 24.8 mmol) was added slowly and dropwise. After the dropwise addition, the reaction mixture was stirred at room temperature overnight. After completion of the reaction, the mixture was poured into water and extracted with ethyl acetate (2×). The organic layers were combined and washed sequentially with saturated aqueous NaHCO3 solution, water and brine. The organic layer was dried over anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to afford 5.44 g (88% yield) of tert-butyl 5-amino-3,4-dihydroisoquinoline-2(1H)-carboxylate of the target compound as a white solid.
