1: acetonitrile / 2 h / Ambient temperature 2: tetrahydrofuran; diethyl ether / 1 h / -50 °C 3: TBAF / tetrahydrofuran; H2O / 3.5 h / 0 °C 4: m-CPBA / CH2Cl2 / 2 h / -50 - -30 °C 5: 1.) TFAA, allyltrimethylsilane, 2.) NaHCO3 / 1.) CH2Cl2, 0 deg C, 15 min, 2.) MeOH, H2O, 1 h View Scheme