1: diethyl ether / 1) 0 deg C, 1 h, 2) rt, 19.5 h 2: 97 percent / 2 M KOH / methanol / 4 h / Ambient temperature 3: 83 percent / Ac2O / tetrahydrofuran / 120 h / Ambient temperature 4: 13 percent / air / various solvent(s) / 2 h / Heating 5: 54 percent / Ph3P / 1.5 h / Heating View Scheme