Synthesis
General procedure for the synthesis of 7-fluoro-1H-indazole from 2,3-difluorobenzaldehyde: To 2,3-difluorobenzaldehyde (1.85 g) was added hydrazine monohydrate (3 ml), and the reaction mixture was heated with stirring at 180°C for 10 hours. After completion of the reaction, the mixture was cooled to room temperature and extracted by adding ethyl acetate and water to separate the organic layer. The organic layer was washed with saturated brine, dried over anhydrous sodium sulfate and subsequently evaporated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography to afford 7-fluoro-1H-indazole (790 mg, 45% yield) using chloroform/acetone as eluent. The structure of the product was confirmed by 1H-NMR (CD3OD, 400 MHz): δ 7.08-7.12 (m, 2H), 7.56-7.59 (m, 1H), 8.10 (d, J = 3.4 Hz, 1H).
References
[1] Patent: EP1870414, 2007, A1. Location in patent: Page/Page column 23
[2] Patent: EP2752410, 2014, A1. Location in patent: Paragraph 0626
