General procedure for the synthesis of 6-chlorobenzodihydropyran-4-one from 3-(p-chlorophenoxy)propionic acid: 3-(p-chlorophenoxy)propionic acid (2 g, 10 mmol) was reacted with concentrated sulfuric acid (20 mL) with stirring for 1 hour at room temperature. After completion of the reaction, the mixture was poured into ice water and extracted with ethyl acetate. The organic layer was washed twice with saturated aqueous sodium bicarbonate and subsequently dried with magnesium sulfate. The dried organic phase was filtered and concentrated under reduced pressure. The crude product was purified by solvent recrystallization from ethyl acetate/hexane (1:5) mixture. The resulting crystals were collected by filtration, washed with hexane and dried to give the target product 6-chlorobenzodihydropyran-4-one (1 g, 55% yield): melting point 98-101 °C (literature value: 100-101 °C); 1H NMR (DMSO-d6) δ 2.82 (t, J=6.5 Hz, 2H, 3-H2), 4.56 (t, J=6.5 Hz, 2H, 2 -H2), 7.1 (d, J=8.9 Hz, 1H, 8-H), 7.6 (dd, J=8.9 Hz/2.7 Hz, 1H, 7-H), 7.68 (d, J=2.7 Hz, 1H, 5-H); 13C NMR (DMSO-d6) δ 36.8 (C-3), 66.9 (C-2), 120.3 (C-8) 122.0 (C-4a/C-6), 125.3 (C-5), 135.6 (C-7), 160.1 (C-8a), 190.6 (C-4).
