1: 1.) n-BuLi / 1.) THF, -78 deg C, 1 h; 2.) -78 deg C, 1 h 2: 61 percent / tetrahydrofuran / 12 h / Ambient temperature 3: 73 percent / DIBAL / diethyl ether / 1.5 h / -30 °C 4: 68 percent / p-toluenesulfonic acid / benzene / 1 h / Heating View Scheme

n-butyllithium 1.) THF, -78 deg C, 1 h; 2.) -78 deg C, 1 h; Yield given. Multistep reaction;