General procedure for the synthesis of 7-chloro-3,4-dihydro-2H-1-naphthalenone from 4-(4-chlorophenyl)butyric acid: polyphosphoric acid (20 g, excess) was placed in a beaker and heated to 90 °C. 4-(4-Chlorophenyl)butyric acid (3 g, 17 mmol) was added in batches. The reaction mixture was stirred for 5 minutes and then polyphosphoric acid (20 g, excess) was added and continued to be heated at 90°C for 5 minutes. The resulting thick orange viscous oil was cooled to 60 °C, followed by the slow addition of water. After completion of the reaction, the mixture was cooled to room temperature and extracted with ethyl acetate (EtOAc). The organic phase was washed sequentially with water, 1N NaOH solution and water, dried with anhydrous magnesium sulfate (MgSO4) and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography to give a white solid product (2.5 g, 81% yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 2.12-2.18 (m, 2H), 2.67 (t, J = 6.8 Hz, 2H), 2.95 (t, J = 6.8 Hz, 2H), 7.22 (d, J = 8.0 Hz, 1H), 7.42 (dd, J = 10.2, 2.4 Hz, 1H), 7.85 (d , J = 2.4 Hz, 1H).
