A mixture of 4-[4-(2-fluoro-4-methanesulfonyl-phenoxy)-pyrazolo[3,4-d]pyrimidin-1-yl]-piperidine-1-carboxylic acid tert-butyl ester (Example 60; 90 mg, 0.18 mmol) and 4 M HCl in dioxane (2 mL) was stirred at room temperature for 5 h. The solvent was evaporated and the residue was dried in vacuo to give a solid. To the solid were added ethyl acetate (3 mL) and triethylamine (74 mg, 0.73 mmol). The mixture was cooled to 10° C. and isopropyl chloroformate (1 M in toluene; 0.22 mL, 0.22 mmol) was added dropwise. The reaction mixture was allowed to warm to room temperature and stirred overnight. Water was added and the mixture was extracted with ethyl acetate. The combined organic layers were dried (sodium sulfate), filtered, evaporated, and purified by flash chromatography, eluting with 30% ethyl acetate/hexanes, to give 4-[4-(2-fluoro-4-methanesulfonyl-phenoxy)pyrazolo[3,4-d]pyrimidin-1-yl]-piperidine-1-carboxylic acid isopropyl ester (30 mg, 35%) as an off-white solid. Mass spectrum (ES) MH+=478.
