Three 3-aryl-5-cyanopyrazolo[3,4-b]pyridines

Abstract

4-(4-Chlorophenyl)-5-cyano-3-(4-methylphenyl)-6-diphenyl-4,7-dihydro-2Hpyrazolo[3,4-b]pyridine–dimethyl formamide (2/1), 2C26H19ClN4·C3H7NO, (I), 5-cyano-4-(4-methoxyphenyl)-3,6-diphenyl-4,7-dihydro-2H-pyrazolo[3,4-b]pyridine, C26H20N4O, (II), and 3,4-bis(4-chlorophenyl)-5-cyano-6-phenyl-1H-pyrazolo[3,4-b]pyridine, C25H14Cl2N4, (III), were prepared from the corresponding 3-amino-5-arylpyrazoles and α-cyanochalcones. NMR solution studies (1H, 13 C, HSQC, HMBC, NOESY) of pyrazolo[3,4-b]pyridines, reveal the 2H-tautomers as being preferred in solution (DMSO-d6). X-ray diffraction studies showed that (I) and (II) also have the 2H-tautomeric structures in the crystal structures. (III) is the aromatic crystalline product formed by oxidation of a 2H precusor during re-crystallization. (I) exists as hydrogen-bonded trimers (two pyrazolo[3,4-b]pyridine systems and a dimethyl formamide), (II) forms two-dimensional sheets and (III) is a centrosymmetric dimer. A paper discussing the chemistry of the above compounds is being prepared