boron tribromide in dichloromethane; benzene T=23°C;

1: 2.) 6 N aq. HCl / 1.) THF, reflux, 3 h, 2.) THF, reflux, overnight 2: 1.) TiCl4 / 1.) CH2Cl2, toluene, from -50 deg C to -40 deg C, 10 min, 2.) CH2Cl2, toluene, a) from -45 deg C to -10 deg C, 4 h 3: 85 percent / BBr3 / benzene; CH2Cl2 / 23 °C View Scheme

1: 1.) TiCl4 / 1.) CH2Cl2, toluene, from -50 deg C to -40 deg C, 10 min, 2.) CH2Cl2, toluene, a) from -45 deg C to -10 deg C, 4 h 2: 85 percent / BBr3 / benzene; CH2Cl2 / 23 °C View Scheme