Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

Synthesis and Characterization of 3-Methyl-1-(4-(trifluoromethyl)phenyl)indeno [1,2-c]pyrazol-4(1H)-one

Pyrazoles have potential applications in the agrochemical and medicinal chemistry industries as pesticides, anti-inflammatory medications, and antitumor drugs. Fluorinated fused-ring pyrazoles may also possess medicinally useful properties. Herein, we report the acid-catalyzed synthesis of a new tricyclic, trifluoromethylated indenopyrazole, 3-methyl-1-(4-(trifluoromethyl)phenyl)indeno[1,2-c]pyrazol-4(1H)-one, from 2-acetyl-1,3-indanedione and 4-trifluoromethylphenylhydrazine. This isomeric pyrazole was obtained in yields ranging from 4–24%. NMR spectroscopic characterization and elemental analysis support the structural assignment, identity, and purity of the product.

An Update on the synthesis and pharmacological properties of pyrazoles obtained from Chalcone

Abstract:

A review concerning the synthesis and pharmacological properties of pyrazoles obtained from Chalcone described in the literature over the last 5 years (2016-2020) was presented and discussed. Among the synthetic approaches for pyrazoles described so far, the cyclization and acetylation method of α,β-unsaturated chalcones and substituted hydrazine was selected and analyzed. 105 pyrazole derivatives (3-107) were evaluated as well as their pharmacological activities, namely, antineoplastic, anti-inflammatory, antioxidant, antibacterial, antifungal, antimycobacterial, antiplasmodial, Alzheimer's disease, enzymes inhibition (like acetylcholinesterase, carbonic anhydrase, and malonyl CoA decarboxylase), anticonvulsant, among others. Pyrazolic compounds are widely used in the new drugs design with a wide spectrum of pharmacological approaches, therefore, it is relevant to research the synthetic methods and therapeutic properties of different pyrazole derivatives.

Discovery of unexpectedly complex reaction pathways for the Knorr pyrazole synthesis via transient flow

Kinetic data for the Knorr pyrazole synthesis were acquired using transient flow methods, including a novel reactant stoichiometry ramping method, providing new insights into the mechanism, including autocatalysis and an unexpected intermediate.

2,4-Diketo esters: Crucial intermediates for drug discovery

Convenient structures such as 2,4-diketo esters have been widely used as an effective pattern in medicinal chemistry and pharmacology for drug discovery. 2,4-Diketonate is a common scaffold that can be found in many biologically active and naturally occurring compounds. Also, many 2,4-diketo ester derivatives have been prepared due to their suitable synthesis. These synthetic drugs and natural products have shown numerous interesting biological properties with clinical potential as a cure for the broad specter of diseases. This review aims to highlight the important evidence of 2,4-diketo esters as a privileged scaffold in medicinal chemistry and pharmacology. Herein, numerous aspects of 2,4-diketo esters will be summarized, including synthesis and isolation of their derivatives, development of novel synthetic methodologies, the evaluation of their biological properties as well as the mechanisms of action of the diketo ester derivates. This paperwork is expected to be a comprehensive, trustworthy, and critical review of the 2,4-diketo ester intermediate to the chemistry community.

A chemo- and regiocontrolled approach to bipyrazoles and pyridones via the reaction of ethyl 5-acyl-4-pyrone-2-carboxylates with hydrazines

Chemo- and regiocontrolled syntheses of pyrazoles and pyridones are presented on the basis of 4-pyrones. A novel approach towards highly functionalized 3,4'-bipyrazoles has been developed by using reactions of ethyl 5-acylcomanoates with hydrazines. The acid-promoted double cyclocondensation allows switching of the structure of the pyrazole rings easily through changing both the nature of hydrazine and the reaction conditions. The transformation of 4-pyrones with phenylhydrazine in EtOH at -20 °C leads to hydroxypyridones as monoaddition products which can be used as precursors for the preparation of pyridone and pyrazole derivatives. A novel rearrangement of 2-hydroxypyridone to pyrazolyl-1,3-diketones in DMSO was found. The structure and regiochemistry of bipyrazoles were confirmed by X-ray analysis and 2D NMR experiments.

Investigation of pH and substituent effects on the distribution ratio of novel steroidal ring D- and A-fused arylpyrazole regioisomers and evaluation of their cell-growth inhibitory effects in vitro

Novel androstanopyrazoles have been efficiently synthesized from steroidal β-ketoaldehydes with different arylhydrazine hydrochlorides both under acidic and basic conditions. Knorr-type transformations of 16-hydroxymethylene-dehydroepiandrosterone containing its 1,3-dicarbonyl moiety on ring D, proved to be regioselective in pyridine at room temperature, while mixtures of regioisomers were obtained in acidic EtOH under reflux. Contrarily, the cyclocondensation reactions of 2-hydroxymethylene-dihydrotestosterone bearing its reactive functionalities on ring A, led to a mixture of pyrazole regioisomers in varying ratio depending on the applied medium. The regioisomeric distribution was found to depend on the electronic character of the substituent of the phenylhydrazine applied. After separating the related isomers by column chromatography, they were subjected to in vitro pharmacological studies to investigate their antiproliferative activities against three human breast malignant cell lines (MCF7, T47D, MDA-MB-231). Flow cytometry revealed that the most potent agents elicited a cell cycle disturbance on MDA-MB-231 and T47D cells.