Ammonium Hydroxide → 4,5,6,7-Tetrahydro-2H-pyrazolo[4,3-b]pyridine

A 250 mL Parr bottle was charged with a solution of 1H-pyrazolo[4,3-b]pyridine (2 g, 16.8 mmol, obtained from J&W PharmLab, LLC) in TFA (20.0 mL) and platinum(IV) oxide (381 mg, 1.68 mmol). The reaction mixture was evacuated twice with hydrogen and shaken under 55 psi pressure of hydrogen for 24 h. The reaction mixture was filtered over celite, and the filter cake washed with 5% methanol in CH2Cl2. The filtrate was concentrated in vacuo to afford a light brown oil that was dissolved in methanol (20 mL). Concentrated ammonium hydroxide solution was added drop wise until the pH remained basic (pH 8). The mixture was concentrated in vacuo then the residue adsorbed on silica gel and purified by chromatography (silica, 150 g column, 50 μm from Analogix, 0 to 5% of a 9:1 methanol:ammonium hydroxide solution in dichloromethane, 15 min) to give a yellow oil. This oil solidified upon drying under high vacuum to yield 4,5,6,7-tetrahydro-1H-pyrazolo[4,3-b]pyridine (1.712 g, 13.9 mmol, 83%) as a yellow solid. 1H NMR (CHLOROFORM-d) d: 7.09 (s, 1H), 3.14-3.25 (m, 2H), 2.76 (t, J=6.6 Hz, 2H), 1.88-2.02 (m, 2H). MS (EI/CI) m/z: 124.1 [M+H]+.

1. customThe reaction mixture was evacuated twice with hydrogen
2. filtrationThe reaction mixture was filtered over celite
3. washthe filter cake washed with 5% methanol in CH2Cl2
4. concentrationThe filtrate was concentrated in vacuo
5. customto afford a light brown oil that
6. concentrationThe mixture was concentrated in vacuo
7. custompurified by chromatography (silica, 150 g column, 50 μm from Analogix, 0 to 5% of a 9:1 methanol:ammonium hydroxide solution in dichloromethane, 15 min)
8. customto give a yellow oil
9. customupon drying under high vacuum

ORD record

ord-0473116cf566457f860a269b70fc4955

Source dataset

uspto-grants-2016_05

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US09334278B2