23204-38-8

23204-36-6

General procedure for the synthesis of 5-hydroxybenzo[de]isochroman-1,3-dione from 5-amino-1H,3H-benzo[DE]isochroman-1,3-dione: Compound 3 (8 mmol, 1.7 g) was placed in a three-necked flask, and 432 mL of aqueous sulfuric acid solution (sulfuric acid to water in a ratio of 1:5, by volume) was added and the reaction system was cooled down to 0 °C. Subsequently, sodium nitrite (12 mmol, 0.81 g) was slowly added and stirred continuously at 0 °C for 1 hour. After completion of the reaction, the reaction system was gradually warmed to room temperature and then stirred at 120 °C for 12 hours. At the end of the reaction, the reaction mixture was cooled to room temperature, filtered through a Kiriyama funnel and the filter cake was washed with water and dried. The crude product was recrystallized with chloroform to afford the target product 5-hydroxybenzo[de]isochromene-1,3-dione.