General procedure for the synthesis of 6,7-dimethoxy-3,4-dihydronaphthalen-1(2H)-one from 4-(3,4-dimethoxyphenyl)butyric acid: polyphosphoric acid (210 g) was added to a solution of dichloromethane (50 mL) in which 4-(3,4-dimethoxyphenyl)butyric acid (0.19 mol, 42 g) was dissolved, and the mixture was heated for 2 hr under reflux conditions. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure and the residue was slowly poured into crushed ice. The pH of the solution was adjusted to 7-8 with alkali, and the precipitate precipitated was filtered and dried to give 6,7-dimethoxy-3,4-dihydronaphthalen-1(2H)-one (36 g, 93.3% yield) as a white solid with a melting point of 94-96 °C (literature value: 96-98 °C).1H NMR (400 MHz, CDCl3): δ 7.51 (s, 1H), 6.67 (s 1H), 3.93 (s, 3H), 3.91 (s, 3H), 2.89 (t, J=6Hz, 2H), 2.60 (t, J=6.4Hz, 2H), 2.15-2.09 (m, 2H); 13C NMR (101MHz, CDCl3): δ197.10, 153.51, 147.96, 139.27 125.79, 110.22, 108.57, 55.98, 38.50, 29.44, 23.61.
