An efficient solvent-free synthesis of 2-hydroxy-2-(trifluoromethyl)-2H-chromenes using silica-immobilized L-proline

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.

Melanin Pathway Determination in Sclerotium cepivorum Berk Using Spectrophotometric Assays, Inhibition Compound, and Protein Validation

Sclerotium cepivorum Berk is the etiological agent of white rot disease that affects plants of the genus Allium. This fungus produces resistance structures called sclerotia that are formed by a rolled mycelium with a thick layer of melanin and it can remain dormant for many years in the soil. Current interest in S. cepivorum has arisen from economic losses in Allium crops in the agricultural sector. Melanin is a component that protects the sclerotia from adverse environmental conditions In many organisms, it plays an important role in the infectious process; in S. cepivorum, the pathway by which this component is synthetized is not fully described. By using infrared spectrophotometric assays applied direct to the sclerotia and a melanin extract followed by an NMR analysis and a tricyclazole melanin inhibition experiment, it allowed us to determine the dihydroxynaphthalene (DHN)-melanin pathway by which S. cepivorum performs its melanin synthesis. Moreover, we focused on studying scytalone dehydratase (SDH) as a key enzyme of the DHN-melanin synthesis. We obtained the recombinant SDH enzyme and tested its activity by a zymogram assay. Thereby, the S. cepivorum melanogenic route was established as a DHN pathway.

Synthesis of 2-trifluoromethyl chromenes via double carbonyl–ene reaction

A synthesis of 2-trifluoromethyl chromenes through double carbonyl–ene reaction of o-isopropenylphenols with trifluoroacetic anhydride is reported.

Synthesis of 1-(β-coumarinyl)-1-(β-indolyl)trifluoroethanols through regioselective Friedel-Crafts alkylation of indoles with β-(trifluoroacetyl)coumarins catalyzed by Sc(OTf)3

A highly efficient Friedel-Crafts alkylation of indole derivatives with β-(trifluoroacetyl)coumarins using Sc(OTf)3 as a catalyst has been developed, which gives regioselective 1,2-adducts to afford 1-(β-coumarinyl)-1-(β-indolyl)trifluoroethanols. A series of tertiary trifluoroethanols containing different indole and coumarin groups were synthesized in moderate to excellent yields (up to 95%) in the presence of 5 mol% catalyst in a short time (only 2 minutes at least). A mechanism of the reaction, in which the trace amount of water plays the role of proton transfer in catalyzing circulation was proposed and confirmed.

Microwave-assisted synthesis of chromenes: biological and chemical importance

Chromenes constitute chemically important class of heterocyclic compounds having diverse biological and chemical importance. Development of environmentally benign, efficient and economical methods for the synthesis of chromenes remains a significant challenge in synthetic chemistry. The synthesis of chromenes, therefore, has attracted enormous attention from medicinal and organic chemists. Researchers have embraced the concepts of microwave (high speed) synthesis to produce biologically and chemically important chromenes in a time sensitive manner. This review will summarize the recent biological applications such as anticancer, antimicrobial, neurodegenerative and insecticidal activity of new chromenes prepared via microwave irradiation. The development of new methodologies for the synthesis of chromenes including green chemistry processes has also been discussed.

A simple and efficient one-pot synthesis of 2-alkyl/aryl/pyridyl substituted 2H-chromenes

A simple and efficient protocol is demonstrated to synthesize medicinally significant new 2-pyridyl/aryl/alkyl substituted 2H-chromenes.

Metalloradical approach to 2H-chromenes

Cobalt(III)-carbene radicals, generated through metalloradical activation of salicyl N-tosylhydrazones by cobalt(II) complexes of porphyrins, readily undergo radical addition to terminal alkynes to produce salicyl-vinyl radical intermediates. Subsequent hydrogen atom transfer (HAT) from the hydroxy group of the salicyl moiety to the vinyl radical leads to the formation of 2H-chromenes. The Co(II)-catalyzed process can tolerate various substitution patterns and produces the corresponding 2H-chromene products in good isolated yields. EPR spectroscopy and radical-trapping experiments with TEMPO are in agreement with the proposed radical mechanism. DFT calculations reveal the formation of the salicyl-vinyl radical intermediate by a metalloradical-mediated process. Unexpectedly, subsequent HAT from the hydroxy moiety to the vinyl radical leads to formation of an o-quinone methide intermediate, which dissociates spontaneously from the cobalt center and easily undergoes an endocyclic, sigmatropic ring-closing reaction to form the final 2H-chromene product.