(S)-tert-butyl 1-(3,3-dimethyl-1-(methylamino)-1-oxobutan-2-ylcarbamoyl)-3-(2,4,5-trifluorophenyl)-6,7-dihydro-1H-pyrazolo[4,3-c]pyridine-5(4H)-carboxylate → (S)-N-(3,3-dimethyl-1-(methylamino)-1-oxobutan-2-yl)-5-methyl-3-(2,4,5-trifluorophenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridine-1-carboxamide

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A solution of (S)-tert-butyl 1-(3,3-dimethyl-1-(methylamino)-1-oxobutan-2-ylcarbamoyl)-3-(2,4,5-trifluorophenyl)-6,7-dihydro-1H-pyrazolo[4,3-c]pyridine-5(4H)-carboxylate (0.92 g, 1.76 mmol) in TFA/DCM (1:1) was stirred at room temperature for 30 min. The reaction mixture was diluted with toluene and evaporated under vacuum. The resulting residue was dissolved in THF, to which formaldehyde (37%, 0.65 mL) and sodium triacetoxyborohydride (424 mg) was added sequentially. After stifling at room temperature for 2 h, THF was evaporated under vacuum. The residue was extracted between EtOAc and saturated aqueous sodium bicarbonate. The organic phase was dried over sodium sulfate and evaporated to dryness. The crude mixture was purified by column with a gradient of from 10% to 40% ethanol in MeCN to give (S)—N-(3,3-dimethyl-1-(methylamino)-1-oxobutan-2-yl)-5-methyl-3-(2,4,5-trifluoro-phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[4,3-c]pyridine-1-carboxamide 37 as a solid (412 mg, 49% yield for two steps). 1H NMR (CDCl3) δ 7.86 (d, J=9.4 Hz, 1H), 7.47-7.54 (m, 1H), 6.98-7.04 (m, 1H), 5.85 (br, 1H), 4.11 (d, J=9.4 Hz, 1H), 3.39 (s, 2H), 3.16-3.20 (m, 2H), 2.84 (d, J=4.8 Hz, 3H), 2.73 (t, J=6.2 Hz, 2H), 2.47 (s, 3H), 1.05 (s, 9H). LCMS (+ESI) m/z=438 [M+H]+.

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