A suspension of 4,6-bis(4-fluorophenyl)-5-(4-pyridyl)-1H-pyrazolo[3,4-b]pyridine (0.39 g, 0.8 mmol, obtained in example 1), KOH (0.05 g, 0.8 mmol) and crown ether 18-C-6 (0.01 g, 0.03 mmol) in toluene (3 mL) was heated to 100° C. for 2 h. A solution of iodoethane (0.18 g, 1.2 mmol) in toluene (1 mL) was added and stirred at 100° C. for 2 days. It was allowed to cool, water and EtOAc were added and the phases were separated. The aqueous phase was extracted with EtOAc. The organic phase was dried over Na2SO4 and concentrated to dryness. The crude product obtained was purified by chromatography on silica gel using hexane-EtOAc mixtures of increasing polarity as eluent, to afford 0.20 g of 2-ethyl-4,6-bis(4-fluorophenyl)-5-(4-pyridyl)pyrazolo[3,4-b]pyridine (yield: 61%) and 28 mg of 1-ethyl-4,6-bis(4-fluorophenyl)-5-(4-pyridyl)pyrazolo[3,4-b]pyridine (yield: 9%).
