Diisopropylamine → 3-Cyclopentyl-2-(4-methanesulfonyl-phenyl)propionic acid

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A solution of diisopropylamine (3.3 mL, 23.5 mmol) in dry tetrahydrofuran (50 mL) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (10 mL) was cooled to −78° C. under nitrogen and then treated with a 10M solution of n-butyllithium in hexanes (2.35 mL, 23.5 mmol). The yellow reaction mixture was stirred at −78° C. for 30 min and then treated dropwise with a solution of 4-methylsulfonylphenylacetic acid (2.40 g, 11.2 mmol) in a small amount of dry tetrahydrofuran. After approximately one-half of the 4-methylsulfonylphenylacetic acid in dry tetrahydrofuran was added, a precipitate formed. Upon further addition of the remaining 4-methylsulfonylphenylacetic acid in dry tetrahydrofuran, the reaction mixture became thick in nature. After complete addition of the 4-methylsulfonylphenylacetic acid in dry tetrahydrofuran, the reaction mixture was very thick and became difficult to stir. An additional amount of dry tetrahydrofuran (20 mL) was added to the thick reaction mixture, and the reaction mixture was then stirred at −78° C. for 45 min, at which time, a solution of iodomethylcyclopentane (2.35 g, 11.2 mmol) in a small amount of dry tetrahydrofuran was added dropwise. The reaction mixture was allowed to warm to 25° C. where it was stirred for 15 h. The reaction mixture was quenched with water (100 mL), and the resulting yellow reaction mixture was concentrated in vacuo to remove tetrahydrofuran. The aqueous residue was acidified to pH=2 using concentrated hydrochloric acid. The aqueous layer was extracted with ethyl acetate. The organic phase was dried over magnesium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 230-400 mesh, 1/3 hexanes/ethyl acetate) afforded 3-cyclopentyl-2-(4-methanesulfonyl-phenyl)propionic acid (1.80 g, 52%) as a white solid: mp 152-154° C.; EI-HRMS m/e calcd for C15H20O4S (M+) 296.1082, found 296.1080.

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