1: disulfonyl fluoride; triethylamine; 1,8-diazabicyclo[5.4.0]undec-7-ene hydrofluoride / acetonitrile / 5 h / 0 - 55 °C 2: 2,2-dimethoxy-propane; water; sulfuric acid / 1,4-dioxane / 16 h / 20 °C / pH 2 - 3 / |Cooling with ice 3: hydrogenchloride; water / ethanol / 18 h / 20 °C 4: pyridine / 0.5 h / 20 °C / |Cooling with ice View Scheme