boron trichloride in dichloromethane 0.25 h; Ambient temperature;

Multi-step reaction with 4 steps 1: 86.9 percent / PPA / 2.5 h / 90 - 100 °C2: 97.5 percent / p-toluenesulphonic acid / 20 h / 100 °C3: 1.) O3, 2.) dimethylsulphide / MeOH, CH2Cl2; 1.) -78 deg C, 1.5 h, 2.) room t.4: 99.6 percent / 70percent HClO4/Ac2O / ethyl acetate / 0.5 h / Ambient temperature  

Multi-step reaction with 2 steps 1: 1.) O3, 2.) dimethylsulphide / MeOH, CH2Cl2; 1.) -78 deg C, 1.5 h, 2.) room t.2: 99.6 percent / 70percent HClO4/Ac2O / ethyl acetate / 0.5 h / Ambient temperature