Step E: 5-( hour. The mixture was further diluted with water (10 mL) and ethyl acetate (10 mL) and the aqueous layer extracted with ethyl acetate (3 x 40 mL). The combined organic layers were then washed with brine, dried over magnesium sulfate, filtered and concentrated. The crude material was purified by flash column chromatography (10-30% ethyl acetate in cyclohexane) to afford the title compound as a pale-yellow oil (0.35 g, 83%). ¹H NMR (400 MHz, CDCl3): δ 7. .