A solution of the product of 2a (2.20 mmol), 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU, 2.20 mmol) and N-methyl-morpholin (2.20 mmol) in dry tetrahydrofuran (100 mL) was stirred at room temperature for 15 minutes. Then (2-amino-ethyl)-carbamic acid tert-butyl ester (2.20 mmol) was added and the mixture stirred at room temperature for another 24 hours. The mixture was then diluted with 40 mL water, the product was isolated through extraction with ethyl acetate and purified by chromatography (silica gel; dichloromethane/methanol 15:1).
