Cl[C:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][N:5]=[C:4]2[CH:13]=[N:14][NH:15][C:3]=12.[NH2:16][C:17]1[S:18][CH:19]=[CH:20][CH:21]=1.[N+](C1SC=CC=1)([O-])=O>[Pd]>[S:18]1[CH:19]=[CH:20][CH:21]=[C:17]1[NH:16][C:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][N:5]=[C:4]2[CH:13]=[N:14][NH:15][C:3]=12Ethyl 7-chloro-1H-pyrazolo[4,3-b]pyridine-6-carboxylate (4.5 g 0.02 mole) and aminothiophene (2.0 g) [prepared from 2-nitrothiophene (supplied by Aldrich and shown by nmr to contain 15% of 3-nitrothiophene) by reduction using either H2 ; 10% Pd/C or stannous chloride] were stirred together under nitrogen for 24 hours. The ethanol was removed under reduced pressure. The resulting brown oil was purified by column chromatography on silica eluting with 5% methanol/ether to give the title compound as a beige solid (0.600 g), mp 188°-190° C.
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