1: 81 percent / CrO3, aq. H2SO4 / acetone / 0.25 h / 0 - 5 °C 2: 37 percent / Bu3SnH, AIBN / benzene / 15 h / Heating 3: 65 percent / TsOH, AcOH / 45 h / Ambient temperature 4: 52 percent / Na, liq.NH3 / diethyl ether / 0.75 h / Heating View Scheme