1: 1) BuLi / CH2Cl2 / 1) -78 to 0 deg C, 0.5 h, 2) 0 deg C., 1 h 2: SnCl4 / 0.5 h / -78 °C 3: mCPBA / CH2Cl2 / 1 h / -50 °C 4: NaHCO3 / 1,3,5-trimethyl-benzene / Heating 5: 42 percent / trifluoroacetic acid; H2O / 2 h / Ambient temperature View Scheme

1: 83 percent / MeSO2Cl, Et3N / benzene / 12 h / 20 °C 2: 2) t-BuOK / 1) THF, 0 deg C, 0.25 h; THF, -78 deg C, 0.5 h 3: 91 percent / CF3COOH, H2O / 6 h / 20 °C View Scheme