Lithium bis(trimethylsilyl)amide solution (20 ml, 20 mmol, 1M in THF) was added to a mixture methoxy methyl triphenyl phosphonium chloride (6.9 g, 20 mmol) in 25 ml THF dropwise at 0° C. and stirred for 15 min and it was added to a mixture of the product of STEP 3 (2.6 g, 7.1 mmol ) in 15 ml THF dropwise at 0° C. After 5 min, the reaction was quenched with H2O. The product was extracted with ethyl acetate. The aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with H2O, brine, dried with Na0.2SO4, and concentrated. The residue was purified by chromatography (on silica gel, ethyl acetate/hexane=1/3) to give a brown oil in 1.14 g. It was dissolved in 20 ml THF and 20 ml 2N HCl. The reaction was stirred at room temperature for 30 min. THF was evaporated. The product was extracted with ethyl acetate and washed H2O. The aqueous layer was extracted with ethyl acetate. The combined organic layer was washed with brine, dried with Na2SO4, and concentrated. The residue was purified by chromatography (on silica gel, ethyl acetate/hexane=1/3) to yield a viscous oil in 0.783 g. NMR spectra of the product were consistent for the proposed structure.
