1: conc. HF / acetonitrile / 2 h / Ambient temperature 2: camphorsulfonic acid / 4 h / Ambient temperature 3: 71 percent / n-Bu4NF / dimethylsulfoxide; tetrahydrofuran / 0.5 h / Ambient temperature 4: 1) Ph3P, diethyl azodicarboxylate (DEAD) / 1) benzene, r.t., 5 min, 2) benzene, r.t., 2 h 5: 72 percent / aq. AcOH / 2 h / 60 °C View Scheme