1: sodium borohydride, boron trifluoride etherate / tetrahydrofuran / 5 h / 10 - 15 °C 2: 78.4 percent / sodium hydroxide; HCl / methanol; H2O / 1 h / Heating 3: 92 percent / dry hydrogen bromide / tetrahydrothiophene 1,1-dioxide / 3 h / 15 °C View Scheme

1: sodium borohydride, boron trifluoride etherate / tetrahydrofuran / 5 h / 10 - 15 °C 2: 78.4 percent / sodium hydroxide; HCl / methanol; H2O / 1 h / Heating 3: 92 percent / dry hydrogen bromide / tetrahydrothiophene 1,1-dioxide / 3 h / 15 °C 4: 95.2 percent / dioxane; H2O / 1 h / 70 °C 5: 90 percent / 85percent phosphoric acid / acetic acid / 7 h / Heating 6: 75.1 percent / polyphosphoric acid, water / 1.33 h / 90 °C View Scheme