ozone; trifluoroacetic acid in dichloromethane T=-78°C;

Multi-step reaction with 6 steps 1: 84 percent / methanol / 3 h / Heating2: 1.) Hg(OAc)2; 2.) NaBH4 / 1.) THF, 4 deg C, 1.5 h3: 45 percent / Jones reagent4: 75 percent / potassium hydride, triethylborane / tetrahydrofuran / 3 h / 0 - 25 °C5: 74 percent / potassium tert-butoxide / 1,2-dimethoxy-ethane / 6 h / 45 °C6: 75 percent / DIBAL / benzene / 5 h / 25 °C  

Multi-step reaction with 5 steps 1: 70 percent / Hg(OAc)2, NaOH, NaBH4 / tetrahydrofuran / 1.5 h / 4 °C2: 45 percent / Jone's reagent3: 75 percent / KH, Et3B / tetrahydrofuran / 0 - 25 °C4: 74 percent / KO-t-Bu / 1,2-dimethoxy-ethane / 45 °C5: 75 percent / DIBAL / benzene / 5 h / 25 °C