A mixture of 2-fluoro-4-methanesulfonyl-phenol (Intermediate 1; 112 mg, 0.6 mmol), 4-(4-chloro-pyrazolo[3,4-d]pyrimidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester (200 mg, 0.6 mmol) and potassium carbonate (180 mg, 1.3 mmol) in DMF (2 mL) was heated in a microwave oven at 160° C. for 10 min. Saturated sodium carbonate solution was added to the reaction mixture to give a precipitate which was filtered off and dissolved in ethyl acetate. The organic solution was dried (sodium sulfate), filtered, evaporated, and purified by flash chromatography, eluting with 20% ethyl acetate/hexanes, to give 4-[4-(2-fluoro-4-methane-sulfonyl-phenoxy)-pyrazolo[3,4-d]pyrimidin-1-yl]-piperidine-1-carboxylic acid tert-butyl ester (140 mg, 47%) as a white solid.
