To 3-(2,4-dimethylphenyl)propionic acid (5.63 g, 14.4 mmol) was added polyphosphoric acid (138 g) and the mixture was stirred at 90 °C for 1 hour. Upon completion of the reaction, the reaction solution was poured into ice water to quench the reaction and the organic phase was extracted with dichloromethane. The organic layer was washed sequentially with water and saturated sodium chloride solution, followed by drying with anhydrous magnesium sulfate and filtration. The solvent was removed by distillation under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (eluent ratio: hexane/ethyl acetate = 100:0 to 0:100, v/v) to afford the target compound 4,6-dimethyl-2,3-dihydro-1H-inden-1-one as a white solid (4.62 g, yield: 91%).1H NMR (CDCl3, 400 MHz) data were as follows: δ2.32 (3H, s ), 2.37 (3H, s), 2.68-2.71 (2H, m), 2.96-2.99 (2H, m), 7.24 (1H, s), 7.40 (1H, s).
