sulfuric acid T=120 - 130°C; 0.5 h;

1: 44 percent / sulphuric acid (50percent) / 0.5 h / 120 - 130 °C 2: 78 percent / boron tribromide / CH2Cl2 / 1 h at -70 deg C, then within 2 h to room temp. View Scheme