C(OC([C:6]1[N:7]([CH2:19][CH2:20][NH:21][C:22]([O:24]C(C)(C)C)=O)[N:8]=[C:9]([CH2:11][O:12][C:13]2[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=2)[CH:10]=1)=O)C.C([O-])([O-])=O.[Na+].[Na+]>Cl.O1CCOCC1>[O:12]([CH2:11][C:9]1[CH:10]=[C:6]2[C:22](=[O:24])[NH:21][CH2:20][CH2:19][N:7]2[N:8]=1)[C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=12-(2-tert-Butoxycarbonylamino-ethyl)-5-phenoxymethyl-2H-pyrazole-3-carboxylic acid ethyl ester (0.72 g, 1.85 mmol) was dissolved in a 4M solution of HCl in 1,4-dioxane (7 mL) under N2. The mixture was stirred at room temperature for 1 hour. The mixture was basified with a saturated solution of Na2CO3 and stirred at room temperature for 72 hours. Then the mixture was 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; 7 M solution of ammonia in MeOH in DCM 0/100 to 5/95). The desired fractions were collected and the solvents evaporated in vacuo to yield 2-phenoxymethyl-6,7-dihydro-5H-pyrazolo[1,5-a]pyrazin-4-one (0.39 g, 85% yield) as a white solid. 1H NMR (500 MHz, CDCl3) δ ppm 3.71-3.86 (m, 2H), 4.32-4.48 (m, 2H), 5.11 (s, 2H), 6.39 (br. s., 1H), 6.91-6.99 (m, 2H), 7.00 (d, J=8.1 Hz, 2H), 7.27-7.34 (m, 2H).
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