Abstract
The direct reaction of 1, 5-dimethyl-(XIm), 5-methyl-1-phenyl-1H-pyrazolo [3, 4-d]-pyrimidinium iodide (XIp), 1-methyl-(XIIm), and 1-phenyl-1H-pyrazolo [3, 4-d] pyrimidinium hydrogen sulfate (XIIp) with active methylene compound and ketone (NuH) were carried out. NuH used in this study were as follows : malononitrile (NuH-1), ethyl cyanoacetate (NuH-2), ethyl acetoacetate (NuH-3), ethyl benzoylacetate (NuH-4), acetylacetone (NuH-5), acetone (NuH-6), cyclopentanone (NuH-7), cyclohexanone (NuH-8), and acetophenone (NuH-9). Thus, XI was transformed into the 5, 6-disubstituted 1-methyl-(or 1-phenyl)-1H-pyrazolo [3, 4-b] pyridines (IX) by the direct reaction with NuH in butanol. Similar transformation took place in the reaction of XII with NuH yielding IX together with 5-amino-1-methyl (or 1-phenyl)-1H-pyrazole (XIV). These 1H-pyrazolo [3, 4-b] pyridines (IX) were also prepared by the Friedlaender synthesis with 5-amino-1-methyl (or phenyl)-1H-pyrazole-4-carboxaldehyde (XV) and NuH in the presence of ethoxide ion. The three possible reaction mechanisms ; path A, B, and C, were proposed. And it might be concluded that the path A stood to reason than the path B or C for the ring transformation of XI and it was not clear which path of A, B or C, was the most suitable for the ring transformation of XII.
