3,4-dihydro-2H-pyran → 4-(Tetrahydro-pyran-2-yloxy)-cyclopent-2-enone

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A solution of 4-hydroxy-2-cyclopentenone (1.41 g, 14.4 mmol) in tetrahydrofuran (24 mL) is treated with 3,4-dihydro-2H-pyran (2 mL) and pyridinium p-toluenesulfonate (500 mg, PPTS). The reaction is stirred at room temperature for 18 hours. The reaction mixture is then diluted with ethyl acetate (25 mL) and washed with 50% saturated brine (2×30 mL). The organic layer is dried over anhydrous magnesium sulfate, filtered and concentrated under vacuum. The resulting crude brown oil is purified by filtration through a plug of silica gel (25 g, 33% ethyl acetate/hexane) to provide the title compound as a yellow oil (2.00 g, 76%); 1H NMR (CDCl3) δ7.46 (2×dd, 1H, J=16.3, 5.7 Hz), 6.2 (m, 1H), 4.9 (m, 1H), 4.80 (d appt, 1H, J=23.8, 2.9 Hz), 3.9 (m, 1H), 3.6 (m, 1H), 2.73 (2×dd, 1H, J=18.4, 6.2 Hz), 2.35 (2×d, 1H, J=18.4 Hz), 1.8 (m, 1H), 1.6 (m, 4H); IR (neat) νmax 2944, 2870, 2855, 1723, 1348, 1202, 1182, 1152, 1128, 1078, 1032 cm-1 ; MS (CI) m/e (% relative intensity) 183 (M+H+, 28), 85(100).

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