Regioselective oxidative trifluoromethylation of imidazoheterocycles via C(sp2)-H bond functionalization

Iron-Catalyzed Sulfonylmethylation of Imidazo[1,2-α]pyridines with N,N-Dimethylacetamide and Sodium Sulfinates

Functionalized imidazo[1,2-α]pyridines are important scaffolds in pharmaceuticals. Herein, we present an efficient 3-sulfonylmethylation protocol for imidazo[1,2-α]pyridines by sodium sulfinates in DMA and H2O (2:1) via an FeCl3-catalyzed three-component coupling reaction. Various sulfonylmethyl imidazo[1,2-α]pyridines were thus afforded in high yields with excellent functional group tolerance. A plausible oxidation-addition mechanism was proposed.

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.

Iodine(III)-promoted oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent

A metal-free protocol for oxidative carbotrifluoromethylation of maleimides with imidazopyridines and Langlois' reagent has been developed using (diacetoxyiodo)benzene (PIDA) as an oxidant. This three-component strategy enables one-step construction of 3,4-disubstituted maleimides in good yields with high functional group tolerance. Both experimental and theoretical studies support the proposed radical reaction mechanism.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

Cross-Coupling Reactions Enabled by Well-Defined Ag(III) Compounds: Main Focus on Aromatic Fluorination and Trifluoromethylation

AgIII compounds are considered strong oxidizers of difficult handling. Accordingly, the involvement of Ag catalysts in cross-coupling via 2e- redox sequences is frequently discarded. Nevertheless, organosilver(III) compounds have been authenticated using tetradentate macrocycles or perfluorinated groups as supporting ligands, and since 2014, first examples of cross-coupling enabled by AgI /AgIII redox cycles saw light. This review collects the most relevant contributions to this field, with main focus on aromatic fluorination/perfluoroalkylation and the identification of AgIII key intermediates. Pertinent comparison between the activity of AgIII RF compounds in aryl-F and aryl-CF3 couplings vs. the one shown by its CuIII RF and AuIII RF congeners is herein disclosed, thus providing a more profound picture on the scope of these transformations and the pathways commonly associated to C-RF bond formations enabled by coinage metals.

Mn-Mediated Direct Regioselective C-H Trifluoromethylation of Imidazopyridines and Quinoxalines

A simple and highly efficient strategy has been developed for direct C-H trifluoromethylation at C-3 of imidazopyridines and C-8 of quinoxalines with readily available Langlois reagent through KMnO₄/AcOH system. This protocol showed broad substrate scope and afforded moderate-to-excellent yields of both products. It is the first report that the functionalization of quinoxalines occurred regioselectively at the C-8 position of quinoxalines. Mechanistic studies revealed that reaction proceeded via radical pathway.

Fe3O4@ABA-aniline-CuI nanocomposite as a highly efficient and reusable nanocatalyst for the synthesis of benzothiazole-sulfide aryls and heteroaryls

Studying diaryl sulfides and benzothiazoles is important in organic synthesis because numerous natural and medicinal products contain these scaffolds. Over the past few years, research on the synthesis of compounds containing benzothiazole-sulfide aryls, as important biological molecules, has received significant attention. Multicomponent reactions are the most popular strategy for performing difficult reactions and the synthesis of complexed molecules such as benzothiazole-sulfide aryls. In this work, CuI was successfully immobilized on the surface of magnetic Fe₃O₄ nanoparticles modified with aniline and 4-aminobenzoic acid [Fe₃O₄@ABA-Aniline-CuI nanocomposite] and its catalytic activity was investigated in the preparation of a broad range of benzothiazole-sulfide aryls and heteroaryls through the one-pot three-component reactions of 2-iodoaniline with carbon disulfide and aryl or heteroaryl iodides in the presence of KOAc as base in PEG-400 as solvent. TEM and SEM images revealed that the shape of the Fe₃O₄@ABA-Aniline-CuI particles is spherical and the size of the particles is approximately between 12-25 nanometers.

Transition Metal Catalyst-Free C-3 Sulfonylmethylation of Imidazo[1,2-a]pyridines with Glyoxylic Acid and Sodium Sulfinates in Water

Herein, we describe an efficient and benign protocol for direct C-3 sulfonylmethylation of imidazo[1,2-a]pyridines with glyoxylic acid and sodium sulfinates. Various sulfonylmethylated imidazo[1,2-a]pyridines were synthesized in water under transition metal catalyst-free conditions. This multicomponent reaction featured available substrates, good functional group tolerance, moderate to excellent yields, and mild reaction conditions.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Visible-light-promoted direct C3-trifluoromethylation and perfluoroalkylation of imidazopyridines

An efficient method for direct trifluoromethylation and perfluoroalkylation at C3 of imidazopyridines through visible light-promoted C-H bond functionalization was developed. Under the irradiation of a blue LED, a series of C3-perfluoroalkyl-substituted imidazopyridines were synthesized from the corresponding imidazopyridines and perfluoroalkyl iodides in moderate to good yields at room temperature. It should be mentioned that this reaction proceeded in the absence of any transition-metal catalyst, oxidant and photocatalyst.

A sustainable C-H functionalization of indoles, pyrroles and furans under a blue LED with iodonium ylides

Pyrrole and indole derivatives are functionalized via a green initiative with the dimethyl malonate derived phenyl iodonium ylide 4a in the presence of a blue LED via C-H functionalization of the respective heterocycles in methanol to generate the desired compounds 5-7 in moderate to good yields. Control experiments provide insight into the probable reaction mechanism. Finally, the strategy is successfully applied in the generation of azepino[4,5-b]indole 12a/b.

Functionalization of imidazo[1,2-a]pyridines via radical reactions

The recent advances in radical reactions for the direct functionalization of imidazo[1,2-a]pyridines are reviewed.

Silver-catalysed C–H bond activation: a recent review

Transition metal catalysed C–H activations are efficient, simple, mild, cost-effective and stereoselective, and many of them are environmentally sustainable transformations.

Peroxide-mediated site-specific C–H methylation of imidazo[1,2-a]pyridines and quinoxalin-2(1H)-ones under metal-free conditions

An effective approach to realize the direct methylation of imidazo[1,2-a]pyridines and quinoxalin-2(1H)-ones with peroxides under metal-free conditions is described.

Recent advances in the synthesis of fluorinated compounds via an aryne intermediate

In this review, the usefulness of aryne intermediates for the synthesis of various fluorinated organic compounds during the last decade has been demonstrated.

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

Fluorine chemistry plays an increasingly important role in pharmaceutical, agricultural, and materials industries. The incorporation of fluorine-containing groups into organic molecules can improve their chemical and physical properties, which attracts continuous interest in organic synthesis. Among various reported methods, transition-metal-catalyzed fluorination/fluoroalkylation has emerged as a powerful method for the construction of these compounds. This review attempts to describe the major advances in the transition-metal-catalyzed incorporation of fluorine, trifluoromethyl, difluoromethyl, trifluoromethylthio, and trifluoromethoxy groups reported between 2011 and 2019.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Regioselective C3-H Trifluoromethylation of 2 H-Indazole under Transition-Metal-Free Photoredox Catalysis

Trifluoromethyl-substituted heteroarenes are biologically active compounds and useful building blocks. In this sequence, we have developed a visible-light-promoted regioselective C3-H trifluoromethylation of 2 H-indazole under metal-free conditions, which proceeds via a radical mechanism. The combination of photocatalysis and hypervalent iodine reagent provides a practical approach to a library of trifluoromethylated indazoles in 35-83% yields.

(Diacetoxy)iodobenzene-Mediated Regioselective Imidation of Imidazoheterocycles with N-Fluorobenzenesulfonimide

Metal-free (diacetoxy)iodobenzene-mediated regioselective imidation of imidazoheterocycles using commercially available N-fluorobenzenesulfonimide as an imidating reagent has been developed. This protocol exhibits broad substrate scope with good to excellent yields of the imidated imidazopyridines under mild conditions in short reaction times. The present protocol also represents an efficient way to access the imidated derivatives of imidazo[2,1-b]thiazole, benzo[d]imidazo-[2,1-b]thiazole, indoles, and indolizines. A radical mechanistic pathway has been proposed for the present protocol.

Copper-catalyzed oxidative multicomponent reaction: synthesis of imidazo fused heterocycles with molecular oxygen

An oxidative cascade that involves multicomponent reaction comprising a terminal alkyne, 2-amino N-heterocycle, benzyl or allylic bromide with molecular oxygen, delivering densely functionalized imidazo fused heterocycles, is described. This reaction features a cheap catalyst, a green oxidant, and readily available starting materials, which make the overall synthesis applicable in the quick access to relevant pharmaceutical molecules with imidazole derived heterocycles.