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Procedure To End Them All
Vinylmagnesium bromide (24 mL of 0.76 M solution in THF, 18 mmol) was cooled to 0°C. ZnBr₂ (18 mL of 1 M solution in THF, 18 mmol, freshly prepared from sublimed ZnBr₂) was added slowly (dropwise) to the cooled vinylmagnesium bromide. The resulting suspension was stirred for 45 minutes at room temperature, then cooled to 0 °C, and then treated with a solution of freshly prepared iodoenone 5 (2.03 g, 9 mmol) in anhydrous DMA (42 mL). (Note: it is imperative to use freshly prepared, light yellow iodoenone 5 to ensure reproducibility of the reaction. Iodoenone 5 rapidly decomposes even upon storage at -20 °C, and the use of darkened material yields no desired product). The resulting solution was shielded from light and treated with Pd(t-Bu₃P)₂ (0.23 g, 0.45 mmol). The reaction mixture was passively warmed up to room temperature and stirred for 45 min. The reaction was quenched with a saturated, aqueous solution of NH₄Cl, then diluted with water, and then extracted three times with hexanes. The combined organic layers were washed with water and then brine, dried over anhydrous Na₂SO₄, and concentrated under reduced pressure. The resulting product was purified via flash chromatography on Et₃N-treated silica gel (elution with Hexanes:CH₂Cl₂ 1:1 with addition of 1% v/v of Et3N) and yielded 0.5 g (44% yield) of enone 6.
