Boron trifluoride → trans-3-Allyloxy-4-hydroxytetrahydrofuran

To a 10-L flask fitted with a double surface condenser, overhead stirrer and nitrogen inlet was added 3,4-epoxytetrahydrofuran (750 g, 8.71 mol), dichloromethane (3750 ml, 5 vol) and allyl alcohol (2530 g, 43.56 mol, 5 eq.). The solution was cooled to between 0° and 5° C. and boron trifluoride diethyletherate (61.8 g, 0.436 mol, 0.05 eq.) was added dropwise whilst maintaining the temperature below 10° C. After addition was complete the solution was allowed to warm to room temperature at which point the reaction slowly exothermed to reflux. After 3 hours 1H NMR analysis showed that no epoxide remained and the reaction was quenched with saturated aqueous sodium hydrogen carbonate solution (1500 mL, 2 vol). The phases were separated and the organic phase was washed with a further portion of saturated aqueous sodium hydrogen carbonate solution (1500 mL, 2 vol). The combined aqueous washes were extracted with CH2Cl2 (5×750 ml, 1 vol). After drying the organic phases over MgSO4, filtering and concentrating in vacuo, the trans-3-allyloxy-4-hydroxytetrahydrofuran (I) was isolated by reduced pressure distillation (bp 94° C. @ 3 mbar) to give 1004.0 g (79.9% yield) of a clear colorless liquid.