To a stirring solution of (±)-2-acetoxy-5-(p-toluenesulfonoxymethyl)-tetrahydrofuran (example 59) (1.63 g, 5.19 mmol) and triethyl phosphite (1.16 mL, 6.75 mmol) in methylene chloride (75 mL) at -35° C. was added titanium (IV) chloride (0.57 mL, 5.19 mmol) dropwise. The yellow solution was then stirred at -35° C. for 30 min and then at 0° C. for 30 min. Saturated NaHCO3 (75 mL) was then added to the reaction mixture and the suspension was then filtered through a CELITE diatomaceous earth. The mixture was then partitioned followed by extraction of the aqueous phase with methylene chloride (2×50 mL). The combined extracts were then washed with brine (100 mL), dried (MgSO4) and concentrated. The residue was then purified by chromatography eluting with 75% EtAc/hexanes→EtAc giving the title compound as 1:1 mixture of cis and trans isomers (1.42 g, 78%).
