General procedure for the synthesis of 3-dihydrochromanone from 2H-benzopyran-3-carboxylic acid: a toluene (24 mL) solution of DPPA (4.812 g, 17.494 mmol) was added slowly and dropwise to a mixed DCM (80 mL) and triethylamine (4.0 mL) of compound 2H-benzopyran-3-carboxylic acid (2.8 g, 15.9 mmol) in a room temperature solution. The reaction mixture was stirred at 50 °C for 1 h. Additional toluene (50 mL) was subsequently added. The reaction system was warmed to 85°C and heating was continued for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature, an aqueous 6.0N HCl solution (28 mL) was added, and the mixture was heated to reflux for 3 hours. At the end of the reaction, the organic layer was separated, washed with saturated NaHCO3 solution, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/EtOAc = 10:0 to 7:3) to afford the target compound 3-dihydrochromanone (2.0 g, yield: 85%).1H NMR (400 MHz, CDCl3): δ 7.55-7.51 (m, 1H), 7.24-7.22 (m, 1H), 7.06-7.03 (m , 1H), 4.42 (s, 2H), 3.61 (s, 2H).
