844648-22-2

844648-19-7

844648-22-2

At 50 °C, 3-(3,5-difluorophenoxy)propionic acid (20.0 g, 99 mmol) was added to 60 mL of concentrated sulfuric acid in batches and stirred until completely dissolved. The resulting yellow-green solution was stirred continuously at 50 °C for 1.5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and slowly poured into 800 mL of ice water. After standing for 1 hour, the colorless precipitate was collected by filtration and washed well with cold water. The resulting 5,7-difluorobenzodihydropyran-4-one was dried over phosphorus pentoxide to give 15.69 g of colorless solid in 86% yield.