[O:1]=[C:2]1[C:7](C(O)=O)=[CH:6][NH:5][C:4]2[CH:11]=[N:12][NH:13][C:3]1=2>C1C=CC(C2C=CC=CC=2)=CC=1.C1C=CC(OC2C=CC=CC=2)=CC=1>[O:1]=[C:2]1[CH:7]=[CH:6][NH:5][C:4]2[CH:11]=[N:12][NH:13][C:3]1=24,7-Dihydro-7-oxo-1H-pyrazolo[4,3-b]pyridine-6-carboxylic acid (7.0 g, 39 mmol) was suspended in Dowtherm A (250 ml) and the mixture was heated under reflux under nitrogen for 2.5 h. After cooling, the mixture was diluted with 60°-80° petrol and filtered. The precipitate was washed well with petrol and dried to give the crude product as an off-white solid (3.9 g, 74%). Recrystallisation from aqueous ethanol/ether gave the title compound as very fine needles, m.p.>320° C.
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