1: n-BuLi / tetrahydrofuran; hexane / 1 h / Heating 2: 270 mg / n-BuLi / tetrahydrofuran; hexane / 2 h / Ambient temperature 3: pyridinium tosylate / methanol / 20 h / Ambient temperature 4: cyclohexanone, aluminium isopropoxide / toluene / 0.5 h / Heating View Scheme