4,5,6,7-Tetrahydro-2H-pyrazolo[4,3-b]pyridine synthesis

Yield:933705-52-3 83%

Reaction Conditions:

with Adams’s catalyst;hydrogen;trifluoroacetic acid under 2844.39 Torr; for 24 h;

Steps:

32.1 4,5,6,7-Tetrahydro- lH-pyrazolo[4,3-b]pyridine

A 250 mL Parr bottle was charged with a solution of lH-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 CH₂CI₂. 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, 150g column, 50 μιη 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-lH-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]⁺.

References:

WO2014/29732,2014,A1 Location in patent:Page/Page column 72