1: 85 percent / pyridinium chlorochromate, Celite / CH2Cl2 / 3 h / Ambient temperature 2: 34 percent / ethanol; tetrahydrofuran / 2 h / -78 °C 3: 78 percent / Br2, azobisisobutylonitrile / CCl4 / 2 h / 70 °C 4: 57 percent / 1 N aq. KOH / 2 h / 0 °C View Scheme

1: 85 percent / pyridinium chlorochromate, Celite / CH2Cl2 / 3 h / Ambient temperature 2: 34 percent / ethanol; tetrahydrofuran / 2 h / -78 °C 3: 78 percent / Br2, azobisisobutylonitrile / CCl4 / 2 h / 70 °C 4: 99 percent / AgNO3 / acetone; H2O / 2 h / Ambient temperature View Scheme