General procedure for the synthesis of 6-methoxy-1-methyl-3,4-dihydroquinolin-2(1H)-one from 6-methoxy-1-methylquinolin-2(1H)-one: a mixture of 6-methoxy-1-methylquinolin-2(1H)-one (3.0 g, 16 mmol), 10% Pd-C catalyst (0.7 g) and ethanol (20 mL) was placed in an autoclave. The reaction was carried out at 100 °C and 50 atm hydrogen pressure for 15 hours. After completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated under reduced pressure to obtain the crude product. The crude product was purified by recrystallization from methanol to afford 6-methoxy-1-methyl-3,4-dihydroquinolin-2(1H)-one (1.8 g, 9.4 mmol, 53% yield) as colorless crystals.1H-NMR (270 MHz, CDCl3) δ: 6.96-6.68 (m, 3H), 3.79 (s, 3H), 3.33 (s, 3H). 2.95-2.56 (m, 4H) ppm.
