[Br:1][C:2]1[CH:3]=[C:4]2[C:10]([I:11])=[N:9][NH:8][C:5]2=[N:6][CH:7]=1.[H-].[Na+].ClCCC(C)(C)C(O)=O.Cl[CH2:24][O:25][C:26](=[O:31])[C:27]([CH3:30])([CH3:29])[CH3:28]>CN(C=O)C>[Br:1][C:2]1[CH:3]=[C:4]2[C:10]([I:11])=[N:9][N:8]([CH2:24][O:25][C:26](=[O:31])[C:27]([CH3:30])([CH3:29])[CH3:28])[C:5]2=[N:6][CH:7]=15-Bromo-3-iodo-1H-pyrazolo[3,4-b]pyridine (4 g, 12.4 mmol) in DMF (50 ml) under nitrogen was stirred at 40° C. for 10 minutes. Sodium hydride (0.9 g, 37 mmol) was added to the DMF solution and the resulting mixture was allowed to stir at 40° C. for 1 hour. Then 2,2-dimethyl-propionic acid chloromethyl ester (chloromethyl pivalate) was added dropwise to the mixture. The reaction was stirred for another 2 hours. The reaction was quenched with saturated NH4Cl (20 ml) and worked up with ethyl acetate, brine, dried with Na2SO4, concentrated to dryness. Silica gel chromatography of the crude using a gradient of ethyl acetate and hexane afforded 2,2-dimethyl-propionic acid 5-bromo-3-iodo-pyrazolo[3,4-b]pyridin-1-ylmethyl ester (5 g, 92% yield). 1H NMR (500 MHz, DMSO-d6) δ 1.07 (s, 9H), 6.37 (s, 2H), 8.30 (s, 1H), 8.77 (s, 1H).
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