Synthesis
GENERAL STEPS: Concentrated sulfuric acid (95 mL) was added to a flask preheated to 60 °C. Intermediate 2 (12 g, 52 mmol) was added slowly in batches while keeping the temperature below 70°C. The reaction was then warmed to 80°C and maintained at this temperature for 3 hours. The reaction system was then warmed to 80 °C and maintained at this temperature for 3 hours. Upon completion of the reaction, the solution was cooled to room temperature and slowly poured into crushed ice under vigorous stirring. The precipitate precipitated was collected by filtration and dried under vacuum to give the final product 7-(trifluoromethoxy)-1H-indole-2,3-dione (product 3).
References
[1] Chinese Chemical Letters, 2017, vol. 28, # 6, p. 1248 - 1251
[2] Patent: US2008/255192, 2008, A1. Location in patent: Page/Page column 16-17
[3] Patent: US2005/59823, 2005, A1. Location in patent: Page 15
