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

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To a solution of 6-chloro-1-(tetrahydro-pyran-2-yl)-3-vinyl-1H-pyrazolo[3,4-b]pyridine-4-carboxylic acid ethyl ester (2.00 g, 5.96 mmol), described in example 16.1, in dioxane (54 mL) were added 4-hydroxyphenylboronic acid (0.90 g, 6.55 mmol) and an aqueous solution of cesium carbonate (0.4 M, 27 mL, 10.8 mmol). The resulting solution was degassed using argon, tetrakis(triphenylphosphine)palladium (0.62 g, 0.54 mmol) was then added and the reaction mixture was refluxed overnight. Dioxane was removed under vacuum, water was added and then the mixture was acidified to pH=2. The aqueous phase was extracted with a mixture of tetrahydrofuran and EtOAc. The combined organic extracts were washed with brine, dried (Na2SO4), filtered, concentrated under vacuum to give the title compound (3.13 g) as a brown foam which was used without further purification.

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