[NH2:1][C:2]1[NH:6][N:5]=[C:4]([C:7]([O:9][CH2:10][CH3:11])=[O:8])[CH:3]=1.[C:12]([CH:15]([CH2:21][C:22]([O:24][CH2:25][CH3:26])=[O:23])[C:16](OCC)=[O:17])(=O)[CH3:13]>CC1C=CC=CC=1C.S(O)(C1C=CC(C)=CC=1)(=O)=O.O>[CH2:25]([O:24][C:22](=[O:23])[CH2:21][C:15]1[C:12]([CH3:13])=[N:1][C:2]2[N:6]([N:5]=[C:4]([C:7]([O:9][CH2:10][CH3:11])=[O:8])[CH:3]=2)[C:16]=1[OH:17])[CH3:26]A suspension of ethyl 5-amino-1H-pyrazole-3-carboxylate (35.5 g, 229 mmol, prepared according to WO 2008015271), diethyl 2-acetylsuccinate (51.2 mL, 275 mmol) and Ts-OH.H2O (0.218 g, 1.144 mmol) in o-xylene (500 mL) was refluxed using Dean-Stork condensor for 5 h. (Note: The suspension turned clear homogeneous solution and then in about 15 min yellow solid started crashing out of the reaction). Then, the reaction mixture was cooled, diluted with hexanes (250 mL), filtered, washed with hexanes and dried to afford ethyl 6-(2-ethoxy-2-oxoethyl)-7-hydroxy-5-methylpyrazolo[1,5-a]pyrimidine-2-carboxylate (53 g, 75% yield) as light yellow solid. 1H NMR (500 MHz, DMSO-d6) δ: 12.61 (br. s., 1H), 6.49 (s, 1H), 4.34 (q, J=7.1 Hz, 2H), 4.09 (q, J=7.1 Hz, 2H), 3.57 (s, 2H), 2.34 (s, 3H), 1.33 (t, J=7.2 Hz, 3H), 1.19 (t, J=7.0 Hz, 3H). LCMS (M+H)=308.04.
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