1: 80 percent / hydrofluoric acid / tetrahydrofuran; CH2Cl2 / 5 h / -70 - 0 °C 2: 100 percent / anhydrous calcium chloride; calcium oxide; iodine / methanol / 1 h / 25 - 27 °C 3: 180 mg / acetic acid / acetone; H2O / 3 h / Heating 4: 90 percent / sodium methoxide; methanol / 4 h / 25 °C View Scheme

1: 80 percent / hydrofluoric acid / tetrahydrofuran; CH2Cl2 / 5 h / -70 - 0 °C 2: 100 percent / anhydrous calcium chloride; calcium oxide; iodine / methanol / 1 h / 25 - 27 °C 3: 180 mg / acetic acid / acetone; H2O / 3 h / Heating View Scheme

With  hydrogen fluoride in  tetrahydrofuran; dichloromethane T=-70 - 0°C; 5 h;   

Stage #1: With  perchloric acid; 1,3-dibromo-5,5-dimethyl-hydantoin in  N,N-dimethyl-formamide 3 h;  cooling; Stage #2: With  sodium hydroxide in  methanol; dichloromethane; water 2 h;  cooling;   

Multi-step reaction with 4 steps 1.1: 70 percent / triethyl orthoformate; p-toluenesulfonic acid / CH2Cl2 / 20 h / 20 °C2.1: 72 percent / tetrahydrofuran; diethyl ether / 72 h / 60 °C3.1: m-iodoxybenzoic acid; diphenyl diselenide / toluene / 22 h / Heating3.2: 50 percent / p-toluenesulfonic acid / CH2Cl2 / 4 h / 20 °C4.1: perchloric acid; 1,3-dibromo-5,5-dimethylhydantoin / dimethylformamide / 3 h / cooling4.2: 75.8 percent / sodium hydroxide / CH2Cl2; methanol; H2O / 2 h / cooling