5-(2-chloropyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine was prepared in the similar to the preparation of 5-(2-chloropyridin-3-yl)-1H-indazole by heating the mixture of tert-butyl 5-bromo-1H-pyrazolo[3,4-b]pyridine-1-carboxylate (2.0 g, 6.7 mmol), 2-chloro-3-pyridine boronic acid pinacol ester (1.9 g, 8.0 mmol), Pd(PPh3)4 (770 mg, 67 mmol), 1,4-dioxane (40 mL) and 2M aq.Na2CO3 (9 mL, 18 mmol) under argon atmosphere. After 12 h, the reaction mixture was cooled to room temperature and concentrated. The crude concentrate was diluted with EtOAc/water (200 mL/100 mL), allowed to stir for 30 min and the heterogeneous solution was filtered. The filter cake was washed with EtOAc (200 mL) and water (75 mL) successively. The filter cake thus obtained was analyzed as the desired product (0.55 g) and dissolved in a mixture of THF/MeOH (2:1, 50 mL). The homogeneous solution was passed through a pad of Celite® and the filtrate concentrated to provide desired product as a crystalline solid (0.45 g). Organic layer from combined filtrates was separated, stirred with MgSO4/Celite® for 20 min and filtered. The filtrate was concentrated and subjected to flash silica gel column purification (Combiflash® companion System® with RediSep® silica gel column 12 g, 30-50-90EtOAC/hexanes eluting solvent gradient upon dry loading the sample by absorbing on silica gel) to obtain another 0.4 g of 5-(2-chloropyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine. Total yield: 52%. 1H NMR (DMSO-d6): δ 13.83 (s, 1H), 8.59 (d, 1H, J=2.0 Hz), 8.45 (dd, 1H, J=1.7 and 4.7 Hz), 8.36 (d, 1H, J=2.0 Hz), 8.21 (s, 1H), 8.00 (dd, 1H, J=1.7 and 7.7 Hz), 7.59 (dd, 1H, J=4.7 and 7.7 Hz).LCMS: rt5.20 min (A), purity 94%, MS (m/e) 231 (MH+).
