Trifluoroacetic acid → 3-[4-(3,5-difluorophenoxy)phenyl]-1-[(3R)-piperidin-3-yl]-1H-pyrazolo[3,4-d]pyrimidin-4-amine

Into a 100 mL round-bottom flask, was placed a solution of tert-butyl (3R)-3-[4-amino-3-[4-(3,5-difluorophenoxy)phenyl]-1H-pyrazolo[3,4-d]pyrimidin-1-yl]piperidine-1-carboxylate (340 mg, 0.65 mmol, 1.00 equiv) in dichloromethane (50 mL), followed by the addition of trifluoroacetic acid (10 mL) dropwise with stirring. The resulting solution was stirred for 12 h at room temperature and then concentrated under vacuum. The resulting solution was diluted with 20 mL of water. The pH value of the solution was adjusted to >7 with sodium carbonate and then extracted with dichloromethane and the organic layers combined and dried over anhydrous sodium sulfate and concentrated under vacuum to give 210 mg (76%) of 3-[4-(3,5-difluorophenoxy)phenyl]-1-[(3R)-piperidin-3-yl]-1H-pyrazolo[3,4-d]pyrimidin-4-amine as a brown solid.