boron tribromide in dichloromethane T=0°C; 8 h;

1: p-toluenesulfonic acid / methanol / Heating 2: 2.) p-toluenesulfonic acid / 1.) benzene, reflux, 2.) benzene, reflux 3: 82 percent / BBr3 / CH2Cl2 / 8 h / 0 °C View Scheme

sodium hydroxide; tetra(n-butyl)ammonium hydrogensulfate in dichloromethane 96 h;