1: BF3 / diethyl ether / 0.25 h / -55 °C 2: oxalyl chloride/DMSO / CH2Cl2 3: KOH / tetrahydrofuran; methanol / 15 h / Ambient temperature View Scheme

1: 1.) titanium tetrachloride / 1.) dichloromethane, -78 deg C, 25 min, 2.) -78 deg C, 45 min 2: 98 percent / pyridinium dichromate / CH2Cl2 / 18 h / 25 °C 3: 97 percent / hydrogen chloride / methanol / 16 h / 4 °C View Scheme

1: 1.) titanium tetrachloride / 1.) dichloromethane, -78 deg C, 25 min, 2.) -78 deg C, 45 min 2: BH3*THF / 4 h / Heating 3: 90 percent / tetrahydrofuran / 0.75 h / Heating 4: 1.) pyridinium dichromate, 2.) 2,5 M aq. KOH / 1.) CH2Cl2, 25 deg C, 18 h, 2.) THF, MeOH, 25 deg C, 5 h 5: TFA / H2O / 0.5 h / 25 °C View Scheme

1: 1.) titanium tetrachloride / 1.) dichloromethane, -78 deg C, 25 min, 2.) -78 deg C, 45 min 2: 98 percent / pyridinium dichromate / CH2Cl2 / 18 h / 25 °C 3: 93 percent / 0.6percent p-TSOH*H2O / dioxane; H2O / 16 h / Heating View Scheme