Cesium carbonate → 6-(4-hydroxy-phenyl)-3-((E)-styryl)-1-(tetrahydro-pyran-2-yl)-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid

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To a solution of 6-chloro-3-((E)-styryl)-1-(tetrahydro-pyran-2-yl)-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid ethyl ester (2.8 g, 6.80 mmol) in dioxane (60 ml) were added 4-hydroxyphenylboronic acid (1.03 g, 7.48 mmol) and an aqueous solution of cesium carbonate (0.4M, 30 mL). The resulting solution was degassed using argon, tetrakis(triphenylphosphine)palladium (0.71 g, 0.61 mmol) was then added and the reaction mixture was refluxed overnight. Dioxane was removed under vacuum, methylene chloride and water were added, and the mixture was acidified until pH=2. The organic layer was washed with water and the aqueous phase was extracted using methylene chloride. The resulting organic layers were combined, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the title compound (2.37 g, 79%) as a yellow solid which was used without any further purification.

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