Cesium carbonate → Tert-butyl 4-(3-(diethoxyphosphoryl)propoxy)phenethylcarbamate

To a solution of tert-butyl 4-hydroxyphenethylcarbamate (1 eq) in DMF (0.17 M) was added cesium carbonate (5 eq). The resulting mixture was stirred at room temperature for 30 minutes, then diethyl 3-bromopropylphosphonate (1.2 eq) was added into the reaction mixture. The resulting mixture was stirred at room temperature for another 4 hours until tert-butyl 4-hydroxyphenethylcarbamate was consumed. The mixture was then diluted with ethyl acetate, and washed with 5% citric acid three times, saturated NaHCO3 solution, water and brine. The organic layer was then dried over anhydrous Na2SO4, and concentrated en vaccuo. The crude material was purified by flash chromatography on a COMBIFLASH® system (ISCO) using 80-100% EtOAc/Hex to give the product as a colorless oil.