1: 93 percent / imidazole / dimethylformamide / 24 h / Ambient temperature 3: Ph2PLi / tetrahydrofuran; hexane / 16 h / Heating 4: Bu4NF / tetrahydrofuran / Ambient temperature View Scheme

boron tribromide in dichloromethane T=0 - 20°C; Inert atmosphere;

boron tribromide in dichloromethane 480 h; Ambient temperature;