1: 78.4 percent / sodium hydroxide; HCl / methanol; H2O / 1 h / Heating 2: 92 percent / dry hydrogen bromide / tetrahydrothiophene 1,1-dioxide / 3 h / 15 °C View Scheme

1: 78.4 percent / sodium hydroxide; HCl / methanol; H2O / 1 h / Heating 2: 92 percent / dry hydrogen bromide / tetrahydrothiophene 1,1-dioxide / 3 h / 15 °C 3: 95.2 percent / dioxane; H2O / 1 h / 70 °C 4: 90 percent / 85percent phosphoric acid / acetic acid / 7 h / Heating 5: 75.1 percent / polyphosphoric acid, water / 1.33 h / 90 °C View Scheme