Metal-free synthesis and characterization of 1,3-Bis(heteroaryl)benzenes followed by the photophysical studies using ultraviolet–visible and fluorescence spectroscopy

Synthesis of bis-1,3-(benz)azoles catalyzed by palladium-PEPPSI complex-based catalysts and the study of photophysical properties

Many biologically potent molecules have been identified to consist of benzo [b]azoles skeleton that are regarded to be the most important drug targets. Specifically, bis-benzo azoles have been the privileged conjugated structures due to their broad applications in environmental catalysis, and synthesis of various polymers, advanced materials, ligands, and natural products. Considering the significant features, different approaches have been attempted to synthesize such molecules via C-H activations by utilizing the transition metal complexes. In this study, we have developed facile and efficient Pd-based N-heterocyclic carbene (NHC) complexes, i.e., Pd-PEPPSI (Palladium-Pyridine Enhanced Pre-catalyst Preparation Stabilization and Initiation) catalysts that could successfully activate C-H bond and construct C-C bond between two 1,3-(benz)azoles via intermolecular oxidative homo-coupling reaction. The prepared Pd NHC catalysts were characterized by NMR and XPS. Pd NHCs concern about the special electronic and steric factors as the strong σ-donating and poor π-accepting properties of these nuclei renders great diversity in the field of transition metal catalysis as ancillary ligands and catalysts. Key factors of this methodology include low catalyst load, good substrate scope (even with sterically hindered substituted components), but no necessity of any extraneous ligands/oxidants and working at ambient reaction conditions with good to excellent yields of the products. Further, the targeted bis azole molecules have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and cyclic voltammetric (CV) studies. The fluorescence and absorption spectra of a few of the synthesized compounds revealed that the electron-donating groups present on N-substituent dictate the absorption and emission bands.

Asymmetrically Functionalized 1,3-Di(2-pyridyl)benzenes: Synthesis and Photophysical Studies

A convenient synthetic approach to asymmetrically functionalized 1,3-di(2-pyridyl)benzenes starting from 3-(3-bromophenyl)-1,2,4-triazines using sequential aza-Diels-Alder reactions and Stille cross-coupling is reported. Photophysical properties of the obtained compounds are studied.

Investigation of Pharmaceutical Importance of 2H-Pyran-2-One Analogues via Computational Approaches

Highly functionalized spirocyclic ketals were synthesized through asymmetric oxidative spirocyclization via carbanion-induced ring transformation of 2H-pyran-2-ones with 1,4-cyclohexandione monoethyleneketal under alkaline conditions. Further acidic-hydrolysis of obtained spirocyclic ketals yields highly substituted 2-tetralone in good yield. Computational analysis based on the DFT calculations and MD simulations has been performed in order to predict and understand global and local reactivity properties of newly synthesized derivatives. DFT calculations covered fundamental reactivity descriptors such as molecular electrostatic potential and average local ionization energies. Nitrogen atom and benzene rings have been recognized as the most important molecular sites from these aspects. Additionally, to predict whether studied compounds are stable towards the autoxidation mechanism, we have also studied the bond dissociation energies for hydrogen abstraction and identified the derivative which might form potentially genotoxic impurities. Interactions with water, including both global and local aspects, have been covered thanks to the MD simulations and calculations of interaction energies with water, counting of formed hydrogen interactions, and radial distribution functions. MD simulations were also used to identify which excipient could be used together with these compounds, and it has been established that the polyvinylpyrrolidone polymer could be highly compatible with these compounds, from the aspect of calculated solubility parameters.