[CH2:1]([O:3][C:4]1[C:9]([C:10]([O:12][CH2:13][CH3:14])=[O:11])=[CH:8][N:7]=[C:6]2[NH:15][N:16]=[CH:17][C:5]=12)[CH3:2].I[CH2:19][CH2:20][CH2:21][C:22]#[CH:23].C(=O)([O-])[O-].[K+].[K+].O>CN(C=O)C>[CH2:13]([O:12][C:10]([C:9]1[C:4]([O:3][CH2:1][CH3:2])=[C:5]2[CH:17]=[N:16][N:15]([CH2:23][CH2:22][CH2:21][C:20]#[CH:19])[C:6]2=[N:7][CH:8]=1)=[O:11])[CH3:14]A mixture of 3.78 g of ethyl 4-ethoxy-1H-pyrazolo-[3,4-b]pyridine-5-carboxylate, 3.90 g of 1-iodo-4-pentyne, and 6.68 g of pulverized anhydrous potassium carbonate in 27 ml of dry DMF was stirred at 50°-60° for 1 hr. The mixture was cooled, poured into water, and the resulting mixture extracted with EtOAc. The combined extracts were washed with water and brine, dried (MgSO4), filtered, and concentrated to leave 5.42 g of a dark oil which slowly crystallized. This material was chromatographed over silica gel using EtOAc/hexane 1:2 (v/v) as the eluant to give 3.03 g (62%) of the title compound as a white solid. A small quantity was recrystallized from toluene to give white crystals, m.p. 84°-85.5°.
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