tert-Butyl 3-(trifluoromethyl)-1,4,5,7-tetrahydro-6H-pyrazolo[3,4-c]pyridine-6-carboxylate

Synthesis

The general procedure for the synthesis of tert-butyl 3-(trifluoromethyl)-4,5-dihydro-1H-pyrazolo[3,4-c]pyridine-6(7H)-carboxylate using tert-butyl 3-oxo-4-(2,2,2-trifluoroacetyl)piperidine-1-carboxylate as a starting material was as follows: to a solution of 1-tert-butyloxycarbonyl-4-(trifluoroacetyl)-3-piperidinone (23.6 g, 0.08 mol) (4.16 ml, 0.086 mol) was added to a solution of ethanol (250 ml) with hydrazine monohydrate (4.16 ml, 0.086 mol). The reaction mixture was stirred at 50°C for 24 hours. After completion of the reaction, the mixture was cooled to room temperature and subsequently concentrated under reduced pressure. The concentrated residue was partitioned between ethyl acetate and saturated brine. The organic layer was separated, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was recrystallized by ethyl acetate/n-pentane mixed solvent to afford the target compound tert-butyl 3-(trifluoromethyl)-4,5-dihydro-1H-pyrazolo[3,4-c]pyridine-6(7H)-carboxylate as a light yellow solid (6.5 g, 28% yield). The product was confirmed by 1H-NMR (400 MHz, CDCl3): δ 11.13 (1H, broad single peak), 4.40 (2H, multiple peaks), 3.66 (2H, multiple peaks), 2.70 (2H, multiple peaks), 1.48 (9H, single peak); the LC/MS analysis showed a retention time of 2.90 min, and a mass spectrometry (ES-) m/z 290 ([M- H]-, calculated value of C12H16F3N3O2 has a molecular weight of 291).

References

[1] Patent: US2010/137276, 2010, A1. Location in patent: Page/Page column 17-18
[2] Journal of Medicinal Chemistry, 2011, vol. 54, # 1, p. 78 - 94
[3] Patent: WO2008/113795, 2008, A1. Location in patent: Page/Page column 42
[4] Patent: WO2008/148832, 2008, A1. Location in patent: Page/Page column 40