Combined XRD and DFT studies towards understanding the impact of intramolecular H-bonding on the reductive cyclization process in pyrazole derivatives

The manuscript comprises the analysis of pyrazole derivatives: (5-methyl-4-nitro-2-phenyl-2H-pyrazol-3-yl)-phenyl-amines and (2H-pyrazol-3-yl)-(2-nitrophenyl)-amines molecular structure as obtained for from single-crystal X-ray diffraction measurements and DFT calculations. High temperature requirements for the reductive cyclization of the derivatives, leading to substituted 1H-pyrazolo[3,4-b] quinoxalines were discussed and explained. Our results show that one of the important factors responsible for low reactivity of the studied compounds is the existence of intramolecular hydrogen bonds. Alternative conditions for the synthesis involving microwave irradiation were proposed and tested within the study. (C) 2019 Elsevier B.V. All rights reserved.