boron tribromide in dichloromethane 1.) -78 deg C, 60 min, 2.) room temp., 90 min;

Multi-step reaction with 5 steps 1: 100 percent / DMAP / tetrahydrofuran / 6 h / Heating2: 76 percent / LAH / tetrahydrofuran; diethyl ether / 24 h / Heating3: 91 percent / tetrahydrofuran / -15 - 20 °C4: 100 percent / aq. sodium metaperiodate / methanol / 24 h / Ambient temperature5: 94 percent / Na2CO3 / toluene / 6 h / Heating