[NH2:1][C:2]1[C:6]([C:7]([O:9][CH2:10][CH3:11])=[O:8])=[C:5]([NH2:12])[NH:4][N:3]=1.CO[CH:15](OC)[CH2:16][CH:17](OC)OC.C(N(CC)CC)C>CN(C=O)C>[NH3:1].[NH2:12][C:5]1[C:6]([C:7]([O:9][CH2:10][CH3:11])=[O:8])=[C:2]2[N:1]=[CH:15][CH:16]=[CH:17][N:3]2[N:4]=1
A mixture of ethyl 3,5-diamino-1H-pyrazole-4-carboxylate (1.0 g, 5.9 mmol), 1,1,3,3-tetramethoxypropane (2.9 mL, 18 mmol), triethylamine (2 mL, 10 mmol), and DMF (15 mL) was heated at 100° C. for 14 hrs, then a further 2 mL of 1,1,3,3-tetramethoxypropane was added. After adding the additional 1,1,3,3-tetramethoxypropane, a significant by-product was noted and heating was stopped immediately. The reaction was cooled to room temperature and the DMF was removed in vacuo. The residue was partitioned between DCM and water, then the organic layer was concentrated and the residue purified by silica chromatography, eluting with 95:5 DCM: 2M methanolic ammonia solution to afford 420 mg (35%) of ethyl 2-aminopyrazolo[1,5-a]pyrimidine-3-carboxylate. 1H NMR (500 MHz, CDCl3) δ 8.57 (dd, J=4.3, 1.6, 1H), 8.43 (dd, J=6.7, 1.6, 1H), 6.84 (dd, J=6.7, 4.4, 1H), 5.52 (s, 2H), 4.48 (q, J=7.1, 2H), 1.45 (t, J=7.1, 3H).
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