1: 95 percent / triethylamine / CH2Cl2 / 0.08 h / 20 °C 2: 100 percent / pyridine / 16 h / 20 °C 3: 41 percent / TsOH / benzene; CH2Cl2 / 2 h / Heating 4: 1.) 0.1M aq. NaOH; 2.) HCl / 1.) dioxane, 20 deg C, 1h; 2.) dichloromethane View Scheme