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In a flask equipped with a mechanical stirrer, Eaton's reagent prepared by adding 144.0 g of P4O10 and 840 mL of methanesulfonic acid was added in batches at room temperature. Subsequently, 144.0 g (~720 mmol) of 3-(2-naphthyl)propionic acid was added to the system. The reaction mixture was stirred overnight and then slowly poured into 2 L of ice-cold water to quench the reaction. The crude product was extracted with 3 x 500 mL dichloromethane and the organic phases were combined. The organic phase was washed sequentially with aqueous K2CO3, dried over anhydrous Na2SO4 and concentrated to dryness under reduced pressure. The residue was purified by fast column chromatography using 600 mL silica gel 60 (40-63 μm) as stationary phase and hexane and dichloromethane (1:1, v/v) as eluent to afford 105.0 g (80% yield) of the target compound, 2,3-dihydro-1H-benzo[e]inden-1-one, as a brown solid. Elemental analysis (C13H10O) Calculated values: C, 85.69; H, 5.53. Measured values: C, 85.98; H, 5.75. 1H NMR (CDCl3) δ: 9.12 (d, J = 8.5 Hz, 1H), 7.93 (d, J = 8.3 Hz, 1H), 7.81 (d, J = 8.1 Hz, 1H), 7.61 (ddd , J = 8.3, 7.1, 1.2 Hz, 1H), 7.50 (ddd, J = 8.1, 7.1, 1.0 Hz, 1H), 7.39 (d, J = 8.3 Hz, 1H), 3.12-3.04 (m, 2H), 2.75-2.65 (m, 2H). 13C{1H} NMR (CDCl3) δ: 207.26, 158.26, 135.47 158.26, 135.47, 132.41, 130.81, 129.23, 128.65, 127.90, 126.39, 123.87, 123.76, 36.73, 25.99.

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