To a stirred solution of N-(3-aminopropyl)-N-methylcarbamic acid tert-butyl ester (2.00 g, 10.6 mmol) and sodium carbonate (2.81 g, 26.6 mmol) in water (7 mL) at 0° C. was added a solution of 9-fluorenylmethyl chloroformate (2.75 g, 10.6 mmol) in 1,4-dioxane (5 mL). The resulting mixture was stirred at room temperature for 2 h and then poured into water (10 mL). This mixture was extracted with diethyl ether (2×50 mL) and the combined organic layers were dried over sodium sulfate, filtered and concentrated under reduced pressure to afford a clear oil. The oil was purified by silica gel flash chromatography (0-70% EtOAc in hexanes) to give the title compound (4.24 g, 77% yield) as a clear oil (product contained a minor impurity, but was used without further purification).
