To a stirred solution of (E)-4-(cyclobutyl(methyl)amino)but-2-enoic acid (139 mg, 0.48 mmol) in acetonitrile (4 mL) was added a drop of DMF before introducing (COCl)2 (73 mg, 0.574 mmol). The resulting mixture was stirred at RT for 2 h. Solvent was removed in vacuo. The residue was dissolved in DCM (5 mL) and the resulting solution was slowly introduced to a pre-cooled solution of tert-butyl-3-iodo-1-(3-(methylamino)phenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-ylcarbamate (46) (186 mg, 0.4 mmol) in DCM (5 mL) dropwise. Stirring was continued at RT overnight. TFA (8 mL) was added and resulting reaction mixture was stirred at RT for additional 2 h and then concentrated in vacuo. The residue was dissolved in sat. aqueous NaHCO3. The crude product was extracted with 85% DCM/IPA (50 mL×3). The combined organic extracts were dried over Na2SO4, filtered and concentrated to provide (E)-N-(3-(4-amino-3-iodo-1H-pyrazolo[3,4-d]pyrimidin-1-yl)phenyl)-4-(cyclobutyl(methyl)amino)-N-methylbut-2-enamide (52) (222 mg, quant. yield) as a white solid. LC-MS (ESI): m/z (M+1) 518.1.
