and allylic acetate S-2 (8.04 g, 41.4 mmol, 1.5 equiv.) were added subsequently and the mixture was heated to 60 °C. After stirring at this temperature for 90 min, the mixture was allowed to cool down to RT and filtered through a plug of silica. The silica was thoroughly rinsed with EtOAc. The filtrate was concentrated under reduced pressure and the crude product was purified by column chromatography (SiO 2 , Et 2 O/pentane, 1:19 to 1:9) to afford diene S-3 (6.90 g, 20.0 mmol, 73%) as a yellowish oil.