Several new 3-aryl-5-cyanopyrazolo[3,4-b]pyridines were easily prepared fro
m 3-amino-5-arylpyrazoles and alpha -cyanochalcones. Structural analysis us
ing NMR solution studies revealed the 2H-tautomers as the preferred tautome
r in solution (DMSO-d(6)). X-ray diffraction confirmed the 2H-tautomers as
the unique tautomer species in the crystalline state as well. Geometry opti
mization of 1H and 2H-tautomers at semi-empirical levels (AM1, MINDO/3) wer
e performed, indicating that in all cases the 2H-tautomers are more stable
than the corresponding 1H-tautomers.