A mixture of ethyl 4-chloro-1-(4-methoxybenzyl)-1H-pyrazolo[3,4-b]pyridine-5-carboxylate (1.5 g, 4.3 mmol), tert-butyl (3S)-piperidin-3-ylcarbamate (1.0 g, 5.0 mmol) and DIPEA (0.84 g, 6.5 mmol) in 1-butanol (10 mL) was heated to 140° C. for 14 h, then allowed to cool. The mixture was concentrated under reduced pressure, and the resulting residue was diluted with EtOAc and washed with aq. NaHCO3. The organic extract was washed with water and brine, dried and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using CombiFlash® apparatus, eluting with 20-100% EtOAc in hexanes, to give the sub-title compound (1.9 g, 86%). LCMS calc. for C27H36N5O5 (M+H)+: m/z=510.3. Found: 510.2.
