After stirring at -78 °C for 30 minutes, the dry-ice acetone bath was replaced with a room temperature water bath, and the reaction mixture was allowed to stir at room temperature for 2 hours. To the reaction mixture was added sat. aq. NH4Cl (3 mL) and Et2O (5 mL). The layers were separated, and the aqueous layer was extracted with Et2O (3 x 5 mL). The combined organic extracts were washed with brine (15 mL), dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure by rotary evaporation to provide a crude yellow oil. Purification by flash column chromatography on silica gel (100% hexanes to 10% Et2O/hexanes) afforded 7-3 (209 mg, 54%) as a colorless oil.