To a solution of 4-[6-(4-hydroxy-phenyl)-1-(tetrahydro-pyran-2-yl)-3-vinyl-1H-pyrazolo[3,4-b]pyridine-4-carbonyl]-piperazine-1-carboxylic acid tert-butyl ester (3.15 g, 5.90 mmol) in dichloromethane (22 ml) were added imidazole (0.96 g, 14.17 mmol) and tert-butyl(chloro)dimethylsilane (1.07 g, 7.08 mmol). The reaction mixture was stirred at room temperature for 5 hours, water and dichloromethane were then added. The aqueous layer was separated and the organic layer was washed with water, brine, dried (Na2SO4), filtered, concentrated under vacuum. The crude residue was purified on a silica gel column chromatography using a gradient of EtOAc (0-30%) in cyclohexane to yield the title compound as a yellow foam (2.05 g, 53%).
