[CH2:1]([O:8][C:9]1[C:10]2[N:11]([N:16]=[CH:17][C:18]=2[C:19]([O:21]C)=[O:20])[CH:12]=[C:13]([Cl:15])[N:14]=1)C1C=CC=CC=1.O.CO.Cl>C1COCC1>[Cl:15][C:13]1[N:14]=[C:9]([O:8][CH3:1])[C:10]2[N:11]([N:16]=[CH:17][C:18]=2[C:19]([OH:21])=[O:20])[CH:12]=1
methyl 4-(benzyloxy)-6-chloropyrazolo[1,5-a]pyrazine-3-carboxylate (5.35) (894 mg, 2.81 mmol) was suspended in THF (7.5 mL), water (2.5 mL), and MeOH (2.5 mL). After stifling at 30° C. for 5 h, HPLC demonstrated one primary product. The reaction mixture was acidified with aqueous HCl and was partitioned between water, EtOAc and 2-Me-THF. The phases were separated and the aqueous phase was extracted 3 times with a mixture of EtOAc and 2-Me-THF. The combined organic phase was concentrated to afford crude 6-chloro-4-methoxypyrazolo[1,5-a]pyrazine-3-carboxylic acid that was used without further purification. LCMS-ESI+ (m/z): [M+H]+ calcd for C8H7ClN3O3: 228.0; found: 228.1.
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