1-Methyl-1H-pyrazolo[3,4-b]pyridin-5-amine. A degassed mixture of 5-bromo-1-methyl-1H-pyrazolo[3,4-b]pyridine (880 mg, 4 mmol), diphenylmethanimine (1.08 g, 6 mmol), tris(dibenzylideneacetone)palladium (0) (734 mg, 0.8 mmol), (R)-(+)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (1.24 g, 2 mmol), and sodium tert-butoxide (576 mg, 6 mmol) in toluene (18 mL) was heated at 115° C. under nitrogen overnight. The reaction mixture was purified by column chromatography on silica gel (eluting with 4% ethyl acetate in petroleum ether) to give N-(diphenylmethylene)-1-methyl-1H-pyrazolo[3,4-b]pyridin-5-amine (1.2 g, crude). The crude N-(diphenylmethylene)-1-methyl-1H-pyrazolo[3,4-b]pyridin-5-amine was dissolved in tetrahydrofuran (10 mL), and hydrochloric acid (2 N, 5 mL) was added. The mixture was stirred at room temperature for 2 h. The mixture was adjusted to pH=8 with saturated sodium carbonate solution, and extracted with ethyl acetate. The organic phase was dried, concentrated, and purified by column chromatography on silica gel (eluting with 33% ethyl acetate in petroleum ether) to give 1-methyl-1H-pyrazolo[3,4-b]pyridin-5-amine (420 mg, 68.4% yield) as an off-white solid.
