1: 1). Et3B; 2.) NaBH4, MeOH / 1.) THF, 23 deg C, 15 min; 2.) -70 deg C 2: 70 percent / p-toluenesulfonic acid / acetone / 2 h / 23 °C 3: 80 percent / Bu4NF / tetrahydrofuran / 3 h / 0 °C 4: 97 percent / Swern oxidation; (further oxidizing agents) View Scheme

1: 1). Et3B; 2.) NaBH4, MeOH / 1.) THF, 23 deg C, 15 min; 2.) -70 deg C 2: 70 percent / p-toluenesulfonic acid / acetone / 2 h / 23 °C 3: 80 percent / Bu4NF / tetrahydrofuran / 3 h / 0 °C View Scheme

Multi-step reaction with 2 steps 1: 1). Et3B; 2.) NaBH4, MeOH / 1.) THF, 23 deg C, 15 min; 2.) -70 deg C2: 70 percent / p-toluenesulfonic acid / acetone / 2 h / 23 °C