1: 68 percent / acetic anhydride / dimethylsulfoxide / 17 h / Ambient temperature 2: 81 percent / tetrahydrofuran / 0.17 h / in an ice-bath 3: 85 percent / KH / tetrahydrofuran; hexamethylphosphoric acid triamide / 0.83 h / -23 °C 4: LiBH4, ZnCl2 / diethyl ether / 0.25 h / in an ice-bath 5: p-toluenesulfonic acid / toluene / 2 h / Ambient temperature View Scheme