After stirring at room temperature for 14 hours, the reaction mixture was diluted with sat. aq. NaHCO3 (15 mL). The layers were separated, and the aqueous layer was extracted with EtOAc (3 x 20 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 give a yellow oil. Purification by flash column chromatography on silica gel (5% EtOAc/hexanes to 20% EtOAc/hexanes) afforded 12-8 (1.14 g, 69% over two steps) as a colorless foam.