[CH2:1]([O:8][C:9]1[CH:13]=[C:12](C(OCC)=O)[N:11]([CH2:19][CH2:20][NH:21][C:22]([O:24]C(C)(C)C)=O)[N:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([O-])([O-])=O.[Na+].[Na+]>Cl.O1CCOCC1.O>[CH2:1]([O:8][C:9]1[CH:13]=[C:12]2[C:22](=[O:24])[NH:21][CH2:20][CH2:19][N:11]2[N:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1Ethyl 3-(benzyloxy)-1-{2-[(tert-butoxycarbonyl)amino]ethyl}-1H-pyrazole-5-carboxylate (0.51 g, 1.31 mmol) was dissolved in a 4 M solution of HCl in 1,4-dioxane (6.53 mL). The mixture was stirred at room temperature for 1 hour and then basified with a saturated solution of Na2CO3. The mixture was stirred at room temperature for 1 hour, diluted with water 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; 7 M solution of ammonia in MeOH in DCM 0/100 to 10/90). The desired fractions were collected and the solvents evaporated in vacuo to yield 2-(benzyloxy)-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (0.31 g, 99% yield) as a white solid.
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