2,3-Dihydroxybutanedioic Acid → 6-fluoro-1H-indazole-5-carbaldehyde

Participants

Reaction Conditions

Reaction Steps

A slurry of 4.8 g (30 mmol) 6-fluoro-1H-indazole-5-carbonitrile [commercially available; preparation given in EP 1 510 516-A1 (production example 82)] in anhydrous toluene (150 ml) was cooled to −40° C. Under inert gas atmosphere, 48 ml (72 mmol) diisobutylaluminium hydride solution (1.5 M in toluene) were added over 30 min, and the resulting mixture was stirred at −40° C. for 3 h. Then, ethyl acetate (30 ml) was added, and the mixture was stirred for further 20 min at −40° C. followed by dropwise addition of aqueous tartaric acid (1 M, 30 ml). The mixture was allowed to warm to 0° C. and filtered at this temperature. The filtrate was extracted with ethyl acetate several times, and the combined organic phases were subsequently washed with saturated aqueous sodium hydrogencarbonate and with brine, dried over sodium sulfate, filtered and concentrated under reduced pressure. The crude product thus obtained (2.60 g, 53% of th.) was used in the next step without further purification.

Provenance & Evidence