1: NEt3, DMAP / CH2Cl2 / 0 °C 2: NaN3 / 18-crown-6 / dimethylformamide / 20 h / 75 °C 3: 87 percent / DDQ, H2O / CH2Cl2 / 2 h / 0 °C 4: 94 percent / Bu4NF*3H2O / tetrahydrofuran / 1 h View Scheme