1: trimethylbenzylammonium fluoride / tetrahydrofuran; H2O / 0 °C 3: 79 percent / sodium bis(trimethylsilyl)amide / tetrahydrofuran / 0.5 h / 56 °C 4: p-toluenesulfonic acid / methanol / 1 h / 0 °C 5: 2percent aqueous sodium hydroxide / diethyl ether / 0.33 h View Scheme