2-Fluorobenzoic acid → 5-(2-Fluorobenzoyl)-4,5,6,7-tetrahydro-2-(phenoxymethyl)-pyrazolo[1,5-a]pyrazine

Participants

Reaction Steps

2-(7-Aza-1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (0.146 g, 0.38 mmol) was added portionwise to a stirred solution of 2-fluorobenzoic acid (0.063 g, 0.45 mmol) in DMF (2.0 mL) at 0° C. The reaction mixture was stirred for 5 minutes and then DIPEA (0.09 mL, 0.52 mmol) and 4,5,6,7-tetrahydro-2-(phenoxymethyl)-pyrazolo[1,5-a]pyrazine (0.08 g, 0.35 mmol) were added. The reaction mixture was stirred at room temperature for 15 hours, diluted with a saturated solution of NH4Cl and extracted with DCM. The organic layer was separated, dried (Na2SO4), filtered and the solvents evaporated in vacuo. The crude product was purified by flash column chromatography (silica; AcOEt in DCM 0/100 to 30/70). The desired fractions were collected, the solvents evaporated in vacuo and the product repurified by flash column chromatography (silica; AcOEt in DCM 0/100 to 70/30). The desired fractions were collected and the solvents evaporated in vacuo. The residue was suspended in a saturated solution of NH4Cl, stirred for 1 hour and extracted with DCM. The organic layer was separated, dried (Na2SO4), filtered and the solvents evaporated in vacuo. The product was repurified by reverse phase HPLC (gradient from 80% of 0.1% solution of ammonium formate/ammonium hydroxide buffer pH 9 solution in water and 20% CH3CN to 0% of 0.1% solution of ammonium formate/ammonium hydroxide buffer pH 9 solution in water and 100% CH3CN) to yield 5-(2-fluorobenzoyl)-4,5,6,7-tetrahydro-2-(phenoxymethyl)-pyrazolo[1,5-a]pyrazine (0.050 g, 41% yield) as a clear oil. C20H18FN3O2 1H NMR (400 MHz, CDCl3) δ ppm 3.80 (br. s., 1.1; H), 4.22 (br. s., 1.5; H), 4.31 (br. s., 1.4; H), 4.61 (s, 0.9; H), 4.99 (s, 1.1; H), 5.03 (s, 0.9; H), 5.07 (s, 1.1; H), 6.07 (s, 0.45; H), 6.27 (s, 0.55H), 6.90-7.09 (m, 3H), 7.15 (td, J=8.8, 3.6 Hz, 1H), 7.21-7.35 (m, 3H), 7.38-7.53 (m, 2H).

Provenance & Evidence