[CH3:1][O-:2].[Na+].[C:4]([O:8][C:9]([N:11]1[CH2:16][CH2:15][CH:14]([N:17]2[C:21]3=[N:22][C:23](Cl)=[N:24][C:25](Cl)=[C:20]3[CH:19]=[N:18]2)[CH2:13][CH2:12]1)=[O:10])([CH3:7])([CH3:6])[CH3:5].[CH3:28][OH:29]>>[C:4]([O:8][C:9]([N:11]1[CH2:16][CH2:15][CH:14]([N:17]2[C:21]3=[N:22][C:23]([O:29][CH3:28])=[N:24][C:25]([O:2][CH3:1])=[C:20]3[CH:19]=[N:18]2)[CH2:13][CH2:12]1)=[O:10])([CH3:7])([CH3:6])[CH3:5]Sodium methoxide (4 mmol) is added to a mixture of 4-(4,6-dichloro-pyrazolo[3,4-d]pyrimidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester (Intermediate 24; 1 mmol) in methanol. The resulting mixture is heated at reflux for 8 h and then cooled. The solvent is evaporated, and ethyl acetate and water are added. The organic layer is washed with water and brine, dried (magnesium sulfate), filtered, evaporated, and purified by flash chromatography on silica gel to give 4-(4,6-dimethoxy-pyrazolo[3,4-d]pyrimidin-1-yl)-piperidine-1-carboxylic acid tert-butyl ester.
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