p-Toluenesulfonic acid monohydrate (0.3 g, 0.165 mmol) was added to a solution of (3aR,4R,5R,6aS)-hexahydro-5-hydroxy-4-((S,E)-3-hydroxy-5-phenylpent-1-enyl)cyclopenta[b]furan-2-one (10.0 g, 33.1 mmol) and 3,4-dihydro-2H-pyran (4.2 g, 49.7 mmol) in dichloromethane (100 mL) at room temperature and the mixture was stirred for 2.5 hr (TLC monitoring). Saturated aqueous solution of sodium bicarbonate (100 mL) was poured into the reaction mixture and the mixture was stirred for 5 minutes. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (100 mL). The combined organic layers were dried over magnesium sulfate, the solid was filtered off and the filtrate was concentrated under reduced pressure to give 16.0 g of crude product. The crude product was purified by column chromatography and then concentrated under reduced pressure to provide 14.0 g of the title compound (89.9% yield).
