Step 1: Ethyl trifluoroacetoacetate (10 g, 58.5 mmol) was slowly added dropwise to a mixture of o-bromoaniline (10.7 g, 58.5 mmol) and polyphosphoric acid (PPA, 40 g) at 100 °C for a controlled time of less than 15 min. After the dropwise addition, the reaction mixture was warmed up to 150 °C with continuous stirring for 12 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was diluted with 10 wt% sodium hydroxide solution (160 mL). The precipitate was collected by filtration and the filtrate was acidified with concentrated hydrochloric acid. The precipitate was collected by filtration again and recrystallized with ethanol to give the target compound 140-3 (10.5 g, 62% yield) as a white solid. Mass spectrometry (ESI) analysis: C10H5BrF3NO [M + H]+ calculated value 292, measured value 292.
