Trifluoroacetic acid → ethyl 5-fluoro-1-(2-fluorobenzyl)-1H-pyrazolo(3,4-b)pyridine-3-carboxylate

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Reaction Steps

13.487 g (51.228 mmol) of ethyl-5-amino-1-(2-fluorobenzyl)-1H-pyrazole-3-carboxylate (preparation described for example 20A in WO 00/06569) was put in 300 ml dioxane and 6 g (51.228 mmol) of 3-(dimethylamino)-2-fluoroacrylaldehyde (preparation described in Justus Liebigs Annalen der Chemie 1970; 99-107) was added at RT. Then 4.736 ml (61.473 mmol) of trifluoroacetic acid was added and the mixture was heated under reflux for 3 days, with stirring. After cooling, it was concentrated by vacuum evaporation and water and ethyl acetate were added to the residue. The phases were separated and the organic phase was washed twice with water. The combined aqueous phases were then extracted twice with ethyl acetate. The combined organic phases were dried over sodium sulphate, filtered and concentrated by vacuum evaporation. The residue (22 g) was then purified by silica gel chromatography (solvent: dichloromethane). 5.67 g (35% of theor.) of the title compound was obtained.

Provenance & Evidence