Tetrabutylammonium Fluoride → (2S)-2-(1-(3-cyano-2-methylphenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-yloxy)-N-(5-cyanopyridin-2-yl)-3-(2-hydroxyethoxy)propanamide

Tetrabutylammonium fluoride (1M in THF) (0.346 mL, 0.35 mmol) was added to (2S)-3-(2-(tert-butyldiphenylsilyloxy)ethoxy)-2-(1-(3-cyano-2-methylphenyl)-1H-pyrazolo[3,4-d]pyrimidin-4-yloxy)-N-(5-cyanopyridin-2-yl)propanamide (Intermediate AT1) (250 mg, 0.35 mmol) in THF (2 mL) under nitrogen. The resulting mixture was stirred at ambient temperature for 90 minutes. The reaction mixture was quenched with saturated NH4Cl, diluted with DCM and poured onto a phase separator. The organic layer was evaporated to a gum. The crude product was purified by flash silica chromatography, elution gradient 50 to 100% EtOAc in isohexane to afford the product (69.0 mg, 41.2%, 92% ee). 1H NMR (400 MHz, CDCl3) δ 2.37-2.44 (4H, m), 3.73-3.86 (4H, m), 4.15-4.26 (2H, m), 6.07 (1H, t), 7.49 (1H, t), 7.63-7.68 (1H, m), 7.77-7.82 (1H, m), 7.94-8.00 (1H, m), 8.34-8.38 (1H, m), 8.43 (1H, s), 8.55-8.60 (2H, m), 9.34 (1H, s); m/z (ES−) (M−H)−=483.52; HPLC tR=1.95 min.