A mixture of zinc dust (0.98 g, 15 mmol, Aldrich, −325 mesh) and dry tetrahydrofuran (3 mL) under argon was treated with 1,2-dibromoethane (0.14 g, 0.75 mmol). The zinc suspension was then heated with a heat gun to ebullition, allowed to cool, and heated again. This process was repeated three times to make sure the zinc dust was activated. The activated zinc dust suspension was then treated with trimethylsilyl chloride (82 mg, 0.75 mmol), and the suspension was stirred for 15 min at 25° C. The reaction mixture was then treated dropwise with a solution of (E)-4-cyclopentyl-2-iodo-but-2-enoic acid methyl ester (prepared in Example 21, 1.47 g, 5 mmol) in dry tetrahydrofuran (1.5 mL) over 3 min. After the addition, the reaction mixture was stirred for 1 h at 40-45° C. and then stirred overnight at 25° C. The reaction mixture was then diluted with dry tetrahydrofuran (5 mL), and the stirring was stopped to allow the excess zinc dust to settle down (˜2 h). In a separate reaction flask, bis(dibenzylideneacetone)palladium(0) (54 mg, 0.1 mmol) and triphenylphosphine (104 mg, 0.4 mmol) in dry tetrahydrofuran (10 mL) was stirred at 25° C. under argon for 10 min and then treated with 3,4-difluoro-iodobenzene (0.96 g, 4 mmol) and the freshly prepared zinc compound in tetrahydrofuran. The resulting brick red solution was heated at 25° C. for 15 h, at which time, thin layer chromatography analysis of the reaction mixture indicated the absence of starting material. The reaction mixture was cooled to 25° C. and then poured into a saturated aqueous ammonium chloride solution (50 mL), and the organic compound was extracted into diethyl ether (2×50 mL). The combined ether extracts were washed with a saturated aqueous sodium chloride solution (1×50 mL), dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. Biotage chromatography (FLASH 40M, Silica, 4/1 hexanes/diethyl ether) afforded (E)-4-cyclopentyl-2-(3,4-difluoro-phenyl)-but-2-enoic acid methyl ester (0.82 g, 73%) as a viscous oil: EI-HRMS m/e calcd for C16H18F2O2 (M+) 280.1275, found 280.1275.
