2-hydroxy-3-methyl-4-quinolone

62-53-3

609-08-5

1873-59-2

The general procedure for the synthesis of 4-hydroxy-3-methyl-2(1H)-quinolinone from aniline and diethyl methylmalonate is as follows: a mixture of aniline (100 mmol) and diethyl methylmalonate (102 mmol) is placed in a flask fitted with a distillation head, and heated for 1 hour in a metal bath at 220-230°C, followed by a temperature increase to 260-270°C and continued heating until ethanol distillation ceased (about 3-6 h). For all products except 1f and 1m, the hot liquid reaction mixture was carefully poured into stirred toluene (50 mL), cooled to room temperature and filtered to collect the precipitate. For 1f and 1m, the hot reaction mixture was cured after cooling to room temperature. The resulting precipitate or cured product was mixed with 0.5 M aqueous sodium hydroxide solution (250 mL) and toluene (50 mL). In the preparation of 1c and 1m, undissolved material was removed by filtration and purified by recrystallization and identified as malonamide derivatives (1c' and 1m', respectively). The filtrate layer was separated and the aqueous layer was washed with toluene (2 x 40 mL). The aqueous layer was treated with decolorized charcoal and filtered, followed by acidification with 10% HCl to a Congo red endpoint. The precipitated 4-hydroxy-3-methyl-2(1H)-quinolinone was collected by filtration, washed with water and further purified by recrystallization if necessary.