1: With boron tribromide in dichloromethane T=0°C; 4 h; 2: With water in dichloromethane T=20°C; Cooling with ice bath;

1.1: N-chloro-succinimide; acetic acid / 3 h / 20 °C 2.1: sodium nitrite; sulfuric acid / water / 0.5 h / 0 °C 2.2: 0.5 h / 20 - 80 °C / Reflux 3.1: n-butyllithium / tetrahydrofuran / 0.75 h / -70 °C 3.2: -70 - 20 °C 4.1: boron tribromide / dichloromethane / 4 h / 0 °C 4.2: 20 °C / Cooling with ice bath View Scheme