3,4-dihydro-2H-pyran → 2-(Tetrahydro-pyran-2-yloxy)-cyclopentanecarboxylic acid ethyl ester

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A solution of 2-hydroxy-cyclopentanecarboxylic acid ethyl ester (3.5 g, 22.12 mmol) in methylene chloride (147.5 mL) was treated with 3,4-dihydro-2H-pyran (3.03 mL, 33.1 mmol) and pyridiniump-toluenesulfonate (556 mg, 2.21 mmol). This solution was stirred at 25° C. for 5 h. The reaction was then washed with a half-saturated aqueous sodium chloride solution (2×75 mL), dried over sodium sulfate, filtered, and concentrated in vacuo. Flash chromatography (Merck Silica gel 60, 230-400 mesh, 90/10 hexanes/ethyl acetate) afforded 2-(tetrahydro-pyran-2-yloxy)-cyclopentanecarboxylic acid ethyl ester (4.7 g, 87.7%) as a clear liquid: EI-HRMS m/e calcd for C13H22O4 (M+) 242.1518. found 242.1521.

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