Iodoethane → tert-butyl N-ethyl-N-(prop-2-yn-1-yl)carbamate

Di-tert-butyl dicarbonate (42.8 g, 196 mmol) in dichloromethane (100 mL) was added dropwise to a solution of propargylamine (11.02 g, 200 mmol) in dichloromethane (200 mL) at room temperature with magnetic stirring. After 2 h, the reaction mixture was washed with aqueous 1N hydrochloric acid (300 mL) and saturated aqueous sodium bicarbonate solution (300 mL). The aqueous layers were washed with dichloromethane (300 mL). The dichloromethane solutions were combined, dried (MgSO4), filtered and concentrated. The residue was purified by flash chromatography (Biotage 40S, EtOAc - hexanes V/V 1:9 as solvent) to give crude N-Boc-propargyl amine. (32.32 g). The crude N-Boc-propargyl amine (3.1 g, 20 mmol) was dissolved in dry dimethylformamide (20 mL) with magnetic stirring and cooled in an ice-water bath. Sodium hydride (0.61 g, 24 mmol) was added in small portions. After stirring for 15 min., iodoethane (3.74 g, 24 mmol) was added. The mixture was allowed to warm to room temperature and stirred for 3 h. then diluted with ether and extracted with water and saturated brine. The aqueous layers were back washed with ether and the ether layers were combined, dried (MgSO4), filtered and concentrated. The residue was purified by flash chromatography (Biotage 40M, ethyl acetate - hexanes as solvent to give N-Boc-N-ethylpropargyl amine. (Yield 3.19 g, 87%).