The general procedure for the synthesis of 4,7-dimethoxy-1-indanone from 2,5-dimethoxybenzenepropanoic acid was as follows: a mixture of 2,5-dimethoxybenzenepropanoic acid (4.68 g, 22.3 mmol) and polyphosphoric acid (PPA, 50.87 g, 24.8 mL) was stirred and reacted for 4.0 h at 80°C. Upon completion of the reaction, the mixture was slowly poured into 250 mL of ice water and extracted with ethyl acetate (EtOAc, 100 mL x 5). The organic layers were combined, washed sequentially with saturated aqueous sodium bicarbonate (NaHCO3) and brine, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with petroleum ether/ethyl acetate (v/v = 3/1) as eluent to afford 4,7-dimethoxy-1-indanone as a light yellow solid (3.0 g, 70.0% yield). The structure of the compound was confirmed by the following spectral data: mass spectrum (MS, ESI) m/z: 193.2 [M + H]+; 1H NMR (400 MHz, CDCl3) δ 7.52 (s, 1H), 6.87 (s, 1H), 3.90 (s, 3H), 3.88 (s, 3H), 3.00-2.97 (m, 2H), 2.68- 2.65 (m, 2H).
