To a flame-dried 50-mL round-bottomed flask equipped with a magnetic stir bar was added pyran and). The reaction vial was evacuated and backfilled with nitrogen for three times. To this flask was added THF (5 mL, 0.05 M) and TFE (5 mL), and this mixture was transferred to a 0 °C ice bath and stirred for 30 minutes before LiBH4 (0.55 mL, 1.1 mmol, 4.5 equiv, 2.0 M in THF) was added over 5 minutes, which resulted in a yellow solution. After stirring for 30 minutes at 0 °C, the reaction vessel was allowed to warm to room temperature.