To a solution of 18 (195 g, 1.03 mol) in MTBE (1.8 L) was added zinc bromide (67 g, 0.30 mol) followed by 2 (390 g, 1.2 mol). tert-BuOLi (290 g, 3.6 mol) was then added in several portions while maintaining the reaction temperature below 40° C. The resulting mixture was stirred at 35° C. for 24 h and quenched into a mixture of 2 N HCl (5.6 L) and heptane (5 L) at 0° C. The organic layer was separated and washed with 5% aqueous NaHCO3 (5 L) twice. The resulting organic solution was concentrated under vacuum. The residue was dissolved in heptane (2 L) and the solution was concentrated again under vacuum. The resulting oil was dissolved in DMSO (2.5 L) and the solution was used in the next step without further purification. HPLC analysis indicated that the solution contained the desired product 19 (290 g, 67% yield) as the major component along with 5% of starting material 18. The analytically pure product 19 as one pair of diastereomers was isolated by chromatography on silica gel with ethyl acetate and heptane mixture as an eluant. HRMS: m/z calcd for C20H26F3NO5 418.1836 (M+H). found 418.1849.
