Hydrazine hydrate (1:1) → 6-Fluoro-3-(2-fluorobenzyl)-1H-pyrazolo[4,3-b]pyridine

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Reaction Steps

9.07 g (32.4 mmol) of the compound from example 3A were initially charged in pyridine (84 ml). Subsequently, 8.10 g (162 mmol) of hydrazine hydrate and 19.8 mg (0.162 mmol) of 4-dimethylaminopyridine were added, and the mixture was heated at reflux for 30 min. The reaction mixture was diluted with ethyl acetate at RT and washed four times with 10% strength aqueous citric acid solution. The organic phase was subsequently washed with saturated aqueous sodium chloride solution, dried over sodium sulfate, filtered and concentrated. MTBE was added to the residue and the solids were filtered off. The latter were dried under high vacuum and gave 1.79 g (79% pure, 18% of theory) of the title compound. The filtrate was concentrated and gave a further 4.86 g (61% pure, 37% of theory) of the title compound. The two fractions were combined and reacted without further purification.

Provenance & Evidence