After stirring at -78 °C for 30 minutes, sat. NH4Cl in THF (30 mL) and Et2O (30 mL) were added to the reaction mixture, and the reaction vessel was removed from the dry-ice acetone bath. After warming to room temperature, the layers were separated and the aqueous layer was extracted with Et2O (2 x 20 mL). The combined organic extracts were washed with brine (25 mL), dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure by rotary evaporation to provide 4-8 as a crude yellow oil (4.2 g).