Hydrochloric Acid → 4-fluoro-1H-indazole-5-carbaldehyde

Participants

Reaction Steps

To a mixture of 5-bromo-4-fluoro-1H-indazole (4 mmol) and sodium hydride (4.3 mmol) in an Argon-purged round-bottom flask was added dry THF (10 mL) at rt. The mixture was stirred at rt for 15 min, during which time it became homogeneous (dark brown). The mixture was then cooled to −78° C., and a solution of n-butyllithium (8.7 mmol, 1.6 M in hexane) was added dropwise. After stirring for 1 h at −78° C., DMF (2 mL) was added dropwise and the mixture was allowed to warm to rt. After 3 h, the mixture was cooled to 0° C. and carefully treated with 1N HCl (20 mL). After a few minutes, solid sodium bicarbonate was added to basify the mixture to pH9-10. The aqueous solution was extracted with EtOAc(2×), and the organic layer was washed with brine, dried (Na2SO4) and concentrated. The residue was purified by flash chromatography (0-40% EtOAc/hexanes) to give 4-fluoro-1H-indazole-5-carbaldehyde.

Provenance & Evidence