1: triethylamine; 1-propanephosphonic acid cyclic anhydride / acetonitrile / 3 h / 20 - 30 °C / Inert atmosphere 2: triethylamine / dichloromethane / 5 h / 0 - 10 °C / Inert atmosphere 3: potassium carbonate; methanol / 4 h / 40 °C 4: hydrogenchloride / water / 7 h / 70 °C View Scheme