Diisopropylamine → 2-[2-(3-Trifluoromethylphenyl)ethyl]pent-4-enoic acid ethyl ester

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To a 100-mL three-neck round-bottomed flask equipped with a thermometer, addition funnel, and nitrogen inlet was added diisopropylamine (2.4 mL, 17.2 mmol) in THF (4 mL). The solution was cooled to −78° C., then a solution of n-BuLi (2.5 M in hexanes, 6.9 mL) was added slowly, followed by HMPA (3.1 mL, 18.0 mmol) and the reaction was stirred at this temperature for 30 min. A solution of ethylpent-4-enoate (2.0 g, 15.6 mmol) in THF (15.6 mL) was added dropwise, then the mixture was stirred for 45 min. To this mixture was added a solution of 1-(2-iodoethyl)-3-trifluoromethylbenzene (35a) (1.37 g, 4.58 mmol) in THF (2 mL) and the resulting mixture was allowed to warm to room temperature overnight. The mixture was diluted with ether (500 mL), washed with water (2×250 mL), and brine (2×250 mL), dried over Na2SO4, filtered, and evaporated. The residue was purified by flash chromatography to provide 2-[2-(3-trifluoromethylphenyl)ethyl]pent-4-enoic acid ethyl ester (529 mg, 39%) as a colorless oil: ESI MS m/z 301 [C16H19F3O2+H]+.

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