1: boron tribromide / CH2Cl2 / 2 h / 20 °C 2: 0.8 g / Dess-Martin periodinane / CH2Cl2 / 20 °C View Scheme

1: 80 percent / pyridinium chlorochromate / CH2Cl2 / 96 h / Ambient temperature 2: 82 percent / NaBH4 / ethanol / 1 h / Ambient temperature 3: 42 percent / CH3SO2Cl, Et3N / CH2Cl2 / 0 °C 4: 77 percent / NaH, EtSH / dimethylformamide / 3 h / 150 °C 5: 57 percent / potassium nitrosodisulfonate, potassium hydrogen phosphate / H2O; acetone / 4 h View Scheme