1: hydrogen bromide / acetic acid 2: 55.1 percent / triethylamine / dimethylformamide; tetrahydrofuran / 4 °C 3: hydrogen bromide / acetic acid 4: 78.9 percent / triethylamine / dimethylformamide / Ambient temperature 5: hydrogen bromide / acetic acid 6: 66.5 percent / pyridine, triethylamine / 4 °C View Scheme