Direct synthesis of 2,4,5-trisubstituted imidazoles and di/tri-substituted pyrimidines via cycloadditions of α,β-unsaturated ketones/aldehydes and N′-hydroxyl imidamides

Synthesis of 5-(trifluoroacetyl)imidazoles from Bromoenones and Benzimidamides via Aza-Michael Initiated Ring Closure Reaction

INTRODUCTION

A simple method for the preparation of 5-(trifluoroacetyl)imidazoles was elaborated.

METHODS

The reaction of trifluoromethyl(α-bromoalkenyl)ketones with benzimidamides was employed to afford the target heterocycles in good yields.

RESULTS

The assembly of imidazole core proceeds via aza-Michael adduct formation followed by intramolecular nucleophilic substitution and spontaneous aromatization as an oxidation sequence.

CONCLUSION

The yields of target imidazoles can be improved by the use of soft oxidizing agents.

Synthesis of 2,4,6-Trisubstituted Pyrimidines through Copper-Catalyzed [4 + 2] Annulation of α,β-Unsaturated Ketoximes with Activated Nitriles

The copper-catalyzed [4 + 2] annulation of α,β-unsaturated ketoximes with activated nitriles for the rapid construction of 2,4,6-trisubstituted pyrimidines in moderate to good yields has been developed. The reaction features synthetic simplicity, good functional group tolerance, and gram-scale applicability. A plausible mechanism is proposed based on mechanistic investigations.

One-pot synthesis, NMR, quantum chemical approach, molecular docking studies, drug-likeness and in-silico ADMET prediction of novel 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(furan-2-yl)-4,5-diphenyl-1H-imidazole derivatives

A novel drug to treat SARS-CoV-2 infections and hydroxyl chloroquine analogue, 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(furan-2-yl)-4,5-diphenyl-1H-imidazole (DDFDI) compound has been synthesized in one pot reaction. The novel compound DDFDI had been characterized by FT-IR, 1H-NMR and 13C-NMR spectral techniques. The geometrical structure was optimized by density functional theory (DFT) method at B3LYP/6-31G (d, p) as the basis set. The smaller energy value provides the higher reactivity of DDFDI compound than hydroxyl chloroquine and was corrected by high electrophilic and low nucleophilic reactions. The stability and charge delocalization of the molecule were also considered by natural bond orbital (NBO) analysis. The HOMO-LUMO energies describe the charge transfer which takes place within the molecule. Molecular electrostatic potential has also been analysed. Drug likeness and oral activity have been carried out based on Lipinski's rule of five. Molecular docking studies are implemented to analyse the binding energy of the DDFDI compound against Covid-19/6W41, COVID-19/6WCF, COVID-19/6Y84 and COVID-19/6W4B receptors and found to be considered as a better antiviral agents.

Unusual Formation of 1,2,4-Oxadiazine Core in Reaction of Amidoximes with Maleic or Fumaric Esters

We have developed a simple and convenient method for the synthesis of 3-aryl- and 3-hetaryl-1,2,4-oxadiazin-5-ones bearing an easily functionalizable (methoxycarbonyl)methyl group at position 6 via the reaction of aryl or hetaryl amidoximes with maleates or fumarates. The conditions for this reaction were optimized. Different products can be synthesized selectively in good yields depending on the base used and the ratio of reactants: substituted (1,2,4-oxadiazin-6-yl)acetic acids, corresponding methyl esters, or hybrid 3-(aryl)-6-((3-(aryl)-1,2,4-oxadiazol-5-yl)methyl)-4H-1,2,4-oxadiazin-5(6H)-ones. The reaction is tolerant to substituents’ electronic and steric effects in amidoximes. As a result, a series of 2-(5-oxo-3-(p-tolyl)-5,6-dihydro-4H-1,2,4-oxadiazin-6-yl)acetic acids, their methyl esters, and 1,2,4-oxadiazoles based on them were prepared and characterized by HRMS, ¹H, and ¹³C NMR spectroscopy. The structures of three of them were elucidated with X-ray diffraction.

Synthesis, crystal structure, Hirshfeld surface analysis, DFT, molecular docking and molecular dynamic simulation studies of (E)-2,6-bis(4-chlorophenyl)-3-methyl-4-(2-(2,4,6-trichlorophenyl)hydrazono)piperidine derivatives

A novel drug to treat SARS-CoV-2 infections and hydroxyl chloroquine analogue, (E)-2,6-bis(4-chlorophenyl)-3-methyl-4-(2-(2,4,6-trichlorophenyl)hydrazono)piperidine (BCMTP) compound has been synthesized in one pot reaction. The novel compound BCMTP has been characterized by FT-IR, ¹H-NMR, ¹³C-NMR and single-crystal X-ray diffraction patterns. Crystal packing is stabilized by C8-H8A•••Cl10ⁱ, C41-H41•••Cl1ⁱⁱ and N1-H1A•••Cl6ⁱⁱⁱ intermolecular hydrogen bonds. From the geometrical parameters, it is observed that the piperidine ring adopts chair conformation. Hirshfeld surface analysis was carried out to quantify the interactions and an interaction energy analysis was done to study the interactions between pairs of molecules. The geometrical structure was optimized by density functional theory (DFT) method at B3LYP/6-31G (d, p) as the basic set. The smaller binding energy value provides the higher reactivity of BCMTP compound than hydroxyl chloroquine and was corrected by high electrophilic and low nucleophilic reactions. The stability and charge delocalization of the molecule were also considered by natural bond orbital (NBO) analysis. The HOMO-LUMO energies describe the charge transfer which takes place within the molecule. Molecular electrostatic potential has also been analysed. Molecular docking studies are implemented to analyse the binding energy of the BCMTP compound against standard drugs such as the crystal structure of ADP ribose phosphatase of NSP3 from SARS-CoV-2 in complex with MES and SARS-CoV-2 main protease with an unliganded active site (2019-nCoV, corona virus disease 2019, COVID-19) and found to be considered having better antiviral agents. Molecular dynamics simulation was performed for COVID-19 main protease (Mpro: 6WCF/6Y84) to understand the elements governing the inhibitory effect and the stability of interaction under dynamic conditions.

Crystal structure and Hirshfeld surface analysis of 4-(3-meth-oxy-phen-yl)-2,6-di-phenyl-pyridine

The title compound, C24H19NO, was obtained via the reaction of (1E,2E)-3-(3-meth-oxy-phen-yl)-1-phenyl-prop-2-en-1-one with ethyl 2-oxo-propano-ate, using NH4I as a catalyst. The compound crystallizes in the monoclinic space group I2/a. In the mol-ecule, the four rings are not in the same plane, the pyridine ring being inclined to the benzene rings by 17.26 (6), 56.16 (3) and 24.50 (6)°. In the crystal, mol-ecules are linked by C-H⋯π inter-actions into a three-dimensional network. To further analyse the inter-molecular inter-actions, a Hirshfeld surface analysis was performed. Hirshfeld surface analysis indicates that the most abundant contributions to the crystal packing are from H⋯H (50.4%), C⋯H/H⋯C (37.9%) and O⋯H/H⋯O (5.1%) inter-actions.

TMSOTf-catalyzed synthesis of trisubstituted imidazoles using hexamethyldisilazane as a nitrogen source under neat and microwave irradiation conditions

In the process of drug discovery and development, an efficient and expedient synthetic method for imidazole-based small molecules from commercially available and cheap starting materials has great significance. Herein, we developed a TMSOTf-catalyzed synthesis of trisubstituted imidazoles through the reaction of 1,2-diketones and aldehydes using hexamethyldisilazane as a nitrogen source under microwave heating and solvent-free conditions. The chemical structures of representative trisubstituted imidazoles were confirmed using X-ray single-crystal diffraction analysis. This synthetic method has several advantages including the involvement of mild Lewis acid, being metal- and additive-free, wide substrate scope with good to excellent yields and short reaction time. Furthermore, we demonstrate the application of the methodology in the synthesis of biologically active imidazole-based drugs.

Trisubstituted imidazoles are synthesized efficiently from the readily available 1,2-diketones and aldehydes using hexamethyldisilazane as a new and stable nitrogen source under TMSOTf-catalysis system, microwave heating and solvent-free conditions.

Iodine-Mediated Cyclization of Enamines to Imidazole-4-Carboxylic Derivatives with Sequential Removal of Nitrogen Atoms from TMSN3

An iodine-mediated oxidative [4+1] cyclization of enamines with TMSN₃ for the synthesis of 2,5-disubstituted imidazole-4-carboxylic derivatives has been developed. The mechanistic studies revealed that the reaction proceeds through a sequential removal of two nitrogen atoms from TMSN₃. The synthetic utility was further demonstrated with a gram-scale reaction and various derivatization transformations of the products.

Recent advances in the synthesis of imidazoles

The review highlights the recent advances (2018-present) in the regiocontrolled synthesis of substituted imidazoles. These heterocycles are key components to functional molecules that are used in a variety of everyday applications. An emphasis has been placed on the bonds constructed during the formation of the imidazole. The utility of these methodologies based around the functional group compatibility of the process and resultant substitution patterns around the ring are described, including discussion of scope and limitations, reaction mechanisms and future challenges.