Pyrrolidine → Methyl 6-(cyclopentylmethylene)-5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylate

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To a solution of methyl 5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylate (3.4 g, 16.7 mmol) in methanol (30 mL) was added cyclopentanecarboxaldehyde (3.3 g, 33.3 mmol) and pyrrolidine (2.78 mL, 33.3 mmol). The solution was stirred for twenty hours at ambient temperature. The reaction was recharged with 0.5 mL of cyclopentanecarboxaldehyde. The resulting precipitate was collected by vacuum filtration to provide methyl 6-(cyclopentylmethylene)-5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylate as a solid (2.8 g, 60% yield). LC/MS on 4.6×50 mm C-18 column, tR=6.71 minutes (10 to 90% acetonitrile/water over 8 minutes at 2 mL/minute with detection 254 nm, at 50° C.); ES-MS m/z 285 (M+H); 1H NMR (400 MHz, DMSO-d6) δ ppm 1.24-1.39 (m, 2H), 1.52-1.74 (m, 4H), 1.76-1.89 (m, 2H), 2.77 (t, J=5.77 Hz, 2H), 2.79-2.90 (m, 1H), 2.97 (t, J=6.44 Hz, 2H), 3.85 (s, 3H), 6.71 (d, J=9.94 Hz, 1H), 7.88 (d, J=6.44 Hz, 1H), 7.91 (s, 1H), 7.98 (d, J=8.06 Hz, 1H).

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