Mild and efficient barbier allylation reaction mediated by magnesium powder under solvent-free conditions

An insight into sustainable and green chemistry approaches for the synthesis of quinoline derivatives as anticancer agents

Quinolones, a key class of heterocyclics, are gaining popularity among organic and medicinal chemists due to their promising properties. Quinoline, with its broad spectrum of action, plays a primordial role in chemotherapy for cancer. Drugs include lenvatinib and its structural derivatives carbozantinib and bosutinib, and tipifarnib are the popular anticancer agents. Owing to the importance of quinoline, there are several classical methods for the synthesis such as, such as Gould-Jacobs, Conrad-Limpach, Camps cyclization, Skraup, Doebnervon Miller, Combes, Friedlander, Pfitzinger, and Niementowski synthesis. These methods are well-commended for developing an infinite variety of quinoline analogues. However, these procedures are associated with several drawbacks such as long reaction times, use of hazardous chemicals or stoichiometric proportions, difficulty of working up conditions, high temperatures, organic solvents, and the presence of numerous steps, all of which have an impact on the environment and the economy. As a result, researchers are working hard to develop green quinoline compounds in the hopes of making groundbreaking discoveries in the realm of cancer. In this review, we have highlighted significant research on quinoline-based compounds and their structure-activity relationship (SAR). Furthermore, because of the significant economic and environmental health and safety (EHS) concerns, more research is being dedicated to the green synthesis of quinolone derivatives. The current review offers recent advances in quinoline derivatives as anticancer agents for green synthesis using microwave, ultrasound, and one-pot synthesis. We believe that our findings will provide useful insight and inspire more green research on this framework to produce powerful and selective quinoline derivatives.

Mechanochemistry-Amended Barbier Reaction as an Expedient Alternative to Grignard Synthesis

Organomagnesium halides (Grignard reagents) are essential carbanionic building blocks widely used in carbon-carbon and carbon-heteroatom bond-forming reactions with various electrophiles. In the Barbier variant of the Grignard synthesis, the generation of air- and moisture-sensitive Grignard reagents occurs concurrently with their reaction with an electrophile. Although operationally simpler, the classic Barbier approach suffers from low yields due to multiple side reactions, thereby limiting the scope of its application. Here, we report a mechanochemical adaptation of the Mg-mediated Barbier reaction, which overcomes these limitations and facilitates the coupling of versatile organic halides (e.g., allylic, vinylic, aromatic, aliphatic) with a diverse range of electrophilic substrates (e.g., aromatic aldehydes, ketones, esters, amides, O-benzoyl hydroxylamine, chlorosilane, borate ester) to assemble C-C, C-N, C-Si, and C-B bonds. The mechanochemical approach has the advantage of being essentially solvent-free, operationally simple, immune to air, and surprisingly tolerant to water and some weak Brønsted acids. Notably, solid ammonium chloride was found to improve yields in the reactions of ketones. Mechanistic studies have clarified the role of mechanochemistry in the process, indicating the generation of transient organometallics facilitated by improved mass transfer and activation of the surface of magnesium metal.

Photocatalytic Barbier reaction - visible-light induced allylation and benzylation of aldehydes and ketones

We report a photocatalytic version of the Barbier type reaction using readily available allyl or benzyl bromides and aromatic aldehydes or ketones as starting materials to generate allylic or benzylic alcohols. The reaction proceeds at room temperature under visible light irradiation with the organic dye 3,7-di(4-biphenyl)1-naphthalene-10-phenoxazine as a photocatalyst and DIPEA as sacrificial electron donor. The proposed cross-coupling mechanism of a ketyl- and an allyl or benzyl radical is supported by spectroscopic investigations and cyclic voltammetry measurements.

A Green Approach for Allylations of Aldehydes and Ketones: Combining Allylborate, Mechanochemistry and Lanthanide Catalyst

Secondary and tertiary alcohols synthesized via allylation of aldehydes and ketones are important compounds in bioactive natural products and industry, including pharmaceuticals. Development of a mechanochemical method using potassium allyltrifluoroborate salt and water, to successfully perform the allylation of aromatic and aliphatic carbonyl compounds is reported for the first time. By controlling the grinding parameters, the methodology can be selective, namely, very efficient for aldehydes and ineffective for ketones, but by employing lanthanide catalysts, the reactions with ketones can become practically quantitative. The catalyzed reactions can also be performed under mild aqueous stirring conditions. Considering the allylation agent and its by-products, aqueous media, energy efficiency and use of catalyst, the methodology meets most of the green chemistry principles.

Highly α-regioselective neodymium-mediated allylation of diaryl ketones

The first utility of neodymium as a mediating-metal in the Barbier reaction of diaryl ketones with allyl halides is reported in this paper. This one-pot reaction was highly α-regioselective and was carried out under mild conditions.

Multicomponent one-pot synthesis of highly-functionalized pyrrole-3-carbonitriles in aqueous medium and their computational study

A one-pot green protocol involving four-components in aqueous medium is developed to synthesize highly-functionalized pyrroles in good yields. Two of the newly synthesized compounds were subjected to in silico analysis on the Pharm Mapper web-server and the human mitogen-activated protein kinase1 (MEK1) enzyme was identified as a potential target protein for these compounds. For target validation, MEK-1 inhibition was performed with two representative compounds (5g and 5h) using docking simulations. These functionalized pyrroles were also tested for their respective IC50 values on human cancer cell lines to evaluate their biocompatibility. Several of these functionalized pyrrole molecules were found to possess higher growth inhibition activity than standard doxorubicin and cisplatin.

Indium-assisted aluminium-based stereoselective allylation of prostereogenic α,α-disubstituted cycloalkanones and imines

Stereoselective allylation of prostereogenic cycloalkanone and imine systems using allylic halides, aluminium powder and a catalytic amount of InCl₃ is reported.

4-Dimethylamino pyridine-promoted one-pot three-component regioselective synthesis of highly functionalized 4H-thiopyrans via heteroannulation of β-oxodithioesters

A highly convergent and regioselective heteroannulation protocol for the synthesis of hitherto unreported highly substituted 2-amino-4-(aryl/alkyl)-5-(aroyl/heteroaroyl)-3-(cyano/carboalkoxy)-6-methylthio-4H-thiopyran derivatives has been developed. This one-pot three-component domino coupling of β-oxodithioesters, aldehydes, and malononitrile/ethyl or methyl cyanoacetate is promoted by 4-dimethylamino pyridine (DMAP) in solvent (dichloromethane (DCM)) as well as under solvent-free conditions. Systematic optimization of reaction parameters identified that the three-component coupling (3CC) protocol is tolerant to a wide array of functionality providing densely functionalized 4H-thiopyrans in excellent yields. The merit of this cascade Knoevenagel condensation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, and efficiency of producing three new bonds (two C-C and one C-S) and one stereocenter in a single operation.