1: K2CO3 / methanol / 1 h / 45 °C 2: triphenylphosphine, diethyl azodicarboxylate / benzene / 2 h / Ambient temperature 3: p-toluenesulfonic acid, Et3N / methanol / 1 h / Ambient temperature 4: NaN3, dimethylsulfoxide / 19 h / 45 °C 5: toluene / 20 h / 70 °C View Scheme