Sodium triacetoxyborohydride (3.55 g, 16.8 mmol) was added portionwise at room temperature to benzyl methyl(2-oxoethyl)carbamate (2.68 g, 12.9 mmol), 2-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)-N-methylethanamine 222c (3.00 g, 12.9 mmol), and acetic acid (2 equiv.) in THF (20 mL). The mixture was stirred for 2 hours, diluted with ethyl acetate, washed with saturated aqueous sodium bicarbonate and brine, dried (Mg2SO4) and evaporated. The residue was purified by Combiflash purification system (ethyl acetate/dichloromethane) to give product as an oil (3.19 g, 58%); MS (ES, m/z): 424 [M+H]+.
