1: Et3N / diethyl ether / 1 h / -50 °C 2: diethyl ether / 24 h / 20 °C 3: 2.4 g / aq. HCl / methanol / 2 h / 50 - 60 °C 4: 83 percent / Et3N / CHCl3 / 48 h / 45 - 50 °C 5: 90 percent / p-TsOH / CHCl3 / 0.5 h / 40 - 45 °C View Scheme