Sodium hydride (60% dispersion in mineral oil; 2 mmol) is added to a solution of 4-(methylsulfonyl)phenol (1.6 mmol) in dimethylformamide (9 mL) and the mixture is stirred at room temperature for 20 min. A solution of crude 4-(4-chloro-6-methoxy-pyrazolo[3,4-d]pyrimidin-1-yl)piperidine-1-carboxylic acid tert-butyl ester (1 mmol) in dimethylformamide (5 mL) is added. The reaction mixture is heated at 50° C. for 8 h. Saturated aqueous ammonium chloride solution is added and the mixture is extracted three times with ethyl acetate. The organic layer is washed with water and brine, dried (magnesium sulfate), filtered, evaporated and purified by flash chromatography on silica gel to give 4-[4-(4-methanesulfonyl-phenoxy)-6-methoxy-pyrazolo[3,4-d]pyrimidin-1-yl]-piperidine-1-carboxylic acid tert-butyl ester.
