A solution of methoxymethylenetriphenylphosphorane is prepared by addition of lithium diisopropyl amide (10.6 g, 0.1 mole) in dry tetrahydrofuran (100 ml) to a slurry of methoxy methyl triphenyl phosphonium chloride (34.3 g, 0.1 mole) in dry toluene (400 ml) under nitrogen at 0° C. The resulting red Wittig reagent is stirred at 0° C. for 30 minutes prior to use. To this solution is added endo-5-t-butyldimethylsilyloxy-exo-3a, 4,7,7a-tetrahydro-4,7-epoxyisobenzofuran-2-ol (14.3 g, 0.05 mole) via a solids addition funnel and the resulting mixture is stirred at 25° C. for 2 hours. The mixture is acidified to pH 5 with 10hydrochloric acid and extracted with ether (three 200 ml portions). The solvents are removed under vacuum and the residue is dissolved in ether and this solution chilled yielding crystalline triphenylphosphine oxide. The filtrate is concentrated yielding the title compound which is purified by column chromatography on silica gel.
