Synthesis, X-Ray Crystal Structure, and Computational Study of Novel Pyrazolo[3,4-B]pyridin-3-Ol Derivatives

Abstract 6-(Pyrazol-1-yl)pyrazolo[3,4-b]pyridin-3-ol (3a) was synthesized by cyclization reaction from 2,6-dichloro-4-methylnicotinonitrile. The related sulfonyl and acylated product (4–7) were obtained from the compound 3a and different sulfonyl and acyl chloride compounds. The sulfonylation of the compound 3a afforded the O1-sulfonylation, only, to give 3-substituted products 4–6. The acylation of the compound 3a gives 1,3-diacylated products 7 via N2, O1-diacylation. All compounds were characterized by spectroscopic methods and the molecular structures of 3a and 4–7 were determined by X-ray diffraction analysis. The molecular structure of 5 and 7 were studied by density functional theory (DFT) calculations, reproduced the experimental geometry. The energies of the three molecules of the tautomeric forms of the compound 3a were calculated by DFT calculations. It was shown that the 3a predominated in the gas phase. Besides, molecular electrostatic potential (MESP) and frontier molecular orbital (FMO) ana...