A mixture of 4-hydroxy-N,N-dimethyl-benzenesulfonamide (ChemService Inc., West Chester, Pa., USA; 18 mg, 0.089 mmol), 4-(4-chloro-pyrazolo[3,4-d]pyrimidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester (Intermediate 19; 30 mg, 0.089 mmol), and potassium carbonate (27 mg, 0.196 mmol) in dimethylformamide (1 mL) was heated in a microwave oven at 160° C. for 10 min. Saturated sodium carbonate solution was added to the reaction mixture, and the mixture was then filtered through a pad of silica gel to remove the precipitate. The silica gel pad was washed with methanol and the solvents were evaporated from the filtrate. The residue was purified by HPLC to give 4-[4-(4-dimethylsulfamoyl-phenoxy)-pyrazolo[3,4-d]pyrimidin-1-yl]-piperidine-1-carboxylic acid tert-butyl ester (13 mg, 28%) as a white solid. Mass spectrum MH+=503.
