Synthesis of Hypervalent Iodine Diazo Compounds and Their Application in Organic Synthesis

Diazomethyl-substituted iodine(III) compounds with electron-withdrawing groups (EWG) connected to diazo methyl center were a type of donor-acceptor diazo compounds with potential reaction abilities similar to ordinary diazo compounds. Although several diazomethyl-substituted iodine(III) compounds were synthesized and used in the nucleophilic substitution reactions as early as 1994, the synthesis and application of new iodine(III) diazo compounds have only been reported to a certain extent in recent years. In the presence of rhodium catalyst, photocatalyst, or nucleophiles, diazomethyl-substituted iodine(III) compounds can be converted into rhodium-carbenes, diazomethyl radicals, ester radicals or nucleophilic intermediates, which can be used as key intermediates for the formation of chemical bonds. The aim of this review is to give an overview of diazomethyl-substituted iodine(III) compounds in organic synthesis.

Annulative Nonaromatic Newman-Kwart-Type Rearrangement for the Synthesis of Sulfur Heteroaryls

By employing enaminones and thiuram disulfides as starting materials, the frontiers of Newman-Kwart rearrangement have been expanded to the alkenyl system for the first time. In addition, instead of leading to the formation of simple carbamothioates, the rearrangement has led to the unprecedented construction of S-heteroaryls. Depending on the differences in the enaminone structure, the efficient synthesis of functionalized isothiazoles and thiophenes has been achieved.

Unlock the C-N Bond Amidation of Enaminones: Metal-Free Synthesis of Enamides by Water-Assisted Transamidation

The C-N bond transamidation of primary amides with N,N-dimethyl enaminones has been efficiently realized by heating in the presence of trifluoromethanesulfonic acid (TfOH). The method enables the practical synthesis of valuable enamides without the use of any metal reagent. In addition, this transamidation protocol can also be expanded to the reactions of sulfonamides, and the late-stage functionalization on sulfonamide drugs such as Celecoxib and Valdecoxib has been verified. Moreover, the participation of water in assisting the transamidation process has been identified by the isotope labeling experiments using D2O, disclosing a new possibility in designing catalytic tactic to other transamidation reactions.

"Alkene-to-Alkene" Difunctionalization of Enaminones for the Synthesis of Polyfunctionalized Alkenes by Transition-Metal-Free C-H and C-N Bond Transformation

The three-component reactions of enaminones, disulfides, and alcohols for the synthesis of polyfunctionalized alkenes have been realized via the C-H and C-N bond transformation on enaminones. The reactions proceed in a novel "alkene-to-alkene" difunctionalization mode without using any transition metal. The application of the alkene products in the synthesis of divergent sulfenyl heteroaryls, including sulfenylated pyrazoles, pyrimidines, and isoxazoles, via simple annulation has also been verified.

Stereoselective Synthesis of Indolyl-C-glycosides Enabled by Sequential Aminopalladation and Heck Glycosylation of 2-Alkynylanilines with Glycals

An efficient and general approach for the synthesis of indolyl-C-glycosides via aminopalladation and subsequent Heck-type glycosylation of easily available 2-alkynylanilines and glycals has been developed. This protocol features excellent stereoselectivity, a broad substrate scope, and mild reaction conditions. In addition, 2,3-pseudoglycals also successfully participated in this cascade reaction, affording C2/C3-branched indolyl glycosides with high regio-/stereoselectivity. The utility of this protocol was also demonstrated by a large-scale reaction and diversified synthetic transformations of the desired products.

Three-Component Chemo-Selective Synthesis of N-(o-Alkenylaryl) Pyrazoles by Pyrazole Annulation and Rh-Catalyzed Chemo-Selective Aryl C-H Addition Cascade

By using readily available enaminones, aryl hydrazine hydrochlorides, and alkynes as starting materials, the chemo-selective three-component synthesis of atropisomeric N-(o-alkenylaryl) pyrazoles has been efficiently accessed with rhodium catalysis. Unlike Satoh-Miura reaction leading to the alkyne-based C-H benzannulation by using prior prepared N-phenyl pyrazoles and alkynes as substrates, this three-component protocol displays unprecedented selectivity of C-H alkenylation by blocking the second round metal alkenylation with the key protonation step in the presence of acids.

Annulation of enaminones with quinonediimides/quinoneimides for selective synthesis of indoles and 2-aminobenzofurans

The annulation reactions of enaminones with quinonediimides/quinoneimides for the selective synthesis of indoles and 2-aminobenzofurans have been realized. With Zn(II) catalysis, quinonediimides reacted with enaminones to give indoles via HNMe₂-elimination-based aromatization. With Fe(III) catalysis, the reactions of quinoneimides with enaminones provided 2-aminobenzofurans via a key dehydrogenative aromatization.

Rongalite as C1 Synthon in the Synthesis of Divergent Pyridines and Quinolines

Rongalite has been used as a cheap and efficient carbon synthon for the synthesis of divergent N-heteroaromatics, including different pyridines and quinolines. The selective synthesis of different products can be achieved by employing enaminones or enaminones/anilines as reaction partners. In addition, compared with the reaction using conventional aldehyde synthons, rongalite displays an evident advantage in providing products with considerably higher product yields under milder conditions. The GC-MS analysis of the reaction process has been performed to probe the possible reaction mechanism.

Tunable vicinal, geminal diphosphorylation and C-N bond phosphorylation of enaminones toward divergent phosphorylated ketone derivatives

This paper reports the trifunctionalization reactions of tertiary enaminones in the fashion of selective gem- and vicinal diphosphorylation, leading to the tunable synthesis of α,α- and α,β-diphosphoryl ketones. In addition, the C-N bond phosphorylation with improved substrate tolerance has been achieved.

Tunable Key [3 + 2] and [2 + 1] Cycloaddition of Enaminones and α-Diazo Compounds for the Synthesis of Isomeric Isoxazoles: Metal-Controlled Selectivity

The three-component reactions of enaminones, α-diazo esters/ketones, and t-butyl nitrite (TBN) for the switchable synthesis of isomeric isoxazoles have been realized. The catalysis with Cu(II) salt provides 3,4-disubsituted isoxazoles via [3 + 2] cycloaddition. On the other hand, the catalysis of Ag(I) with identical substrates leads to isomeric isoxazoles with reversed C3 and C4 substitution based on a key [2 + 1] cycloaddition.

Three-Component Fusion to Pyrazolo[5,1-a]isoquinolines via Rh-Catalyzed Multiple Order Transformation of Enaminones

A facile and practical method for the synthesis of fused tricyclic pyrazolo[5,1-a]isoquinolines has been realized via the reactions of enaminones, hydrazine hydrochloride, and internal alkynes. By means of Rh catalysis, the extraordinary high-order bond functionalization, including the transformation of aryl C-H, ketone C═O, and alkenyl C-N bonds in the enaminones, marks the major feature of the cascade reactions. The results disclose the individual advantage of enaminones in the design of novel and efficient synthetic methods.

Cascade in Situ Iodination, Chromone Annulation, and Cyanation for Site-Selective Synthesis of 2-Cyanochromones

A facile cascade reaction for the site selective synthesis of 2-cyanochromones is described. By using simple o-hydroxyphenyl enaminones and potassium ferrocyanide trihydrate (K₄[Fe(CN)₆]₃·3H₂O) as starting materials and I₂/AlCl₃ as promoters, the products are furnished via tandem chromone ring formation and C-H cyanation. The in situ formation of 3-iodochromone and a formal 1,2-hydrogen atom transfer (HAT) process account for the unconventional site selectivity. In addition, the synthesis of 2-cyanoquinolin-4-one has been realized by employing corresponding 2-aminophenyl enaminone as substrate.

Three-component synthesis of N-naphthyl pyrazoles via Rh(III)-catalyzed cascade pyrazole annulation and Satoh-Miura benzannulation

The synthesis of N-naphthyl pyrazoles has been realized by the direct three-component reactions of enaminones, aryl hydrazine hydrochlorides and internal alkynes via Rh(III) catalysis. The synthetic reactions employing simple substrates lead to simultaneous construction of dual cyclic moieties, including a pyrazole ring and a phenyl ring, via sequential formation of two C-N and three C-C bonds.

Recent Advances in Electrochemical Cascade Cyclization Reactions

This review highlights the recent progress in the electrochemical cascade cyclization reactions for the synthesis of carbon rings and heterocycles such as pyridines, quinolines, phenanthridines, cinnolines, 1,4-dihydroquinolines, oxindoles, imidazo[1,5-a]pyridines, imidazoles, etc. The works included herein are introduced in tow major sections of heterocycle construction and carbocycle construction reactions, covering the works reported from 2012 to 2022.

Catalyst-Free Cascade Annulation of Enaminones and Aryl Diazonium Tetrafluoroboronates for Cinnoline Synthesis and the Anti-Inflammatory Activity Study

A simple and concise method for the synthesis of cinnolines has been developed by the reactions of readily available enaminones and aryl diazonium tetrafluoroboronates. The reactions run efficiently to provide cinnolines with broad diversity in the substructure by heating in dimethyl sulfoxide without using any catalyst or additive. In addition, the primary investigation of the anti-inflammatory activity of these products leads to the observation of p-chlorobenzoyl (3f) and p-nitrobenzoyl (3j) cinnolines as attractive anti-inflammatory compounds in vitro.

Synergistic Visible Light and Pd-Catalyzed C-H Alkylation of 1-Naphthylamines with α-Diazoesters

The combination of visible light irradiation and Pd-catalysis has been practically employed for the C-H alkylation reactions of naphthylamines and α-diazo esters, leading to the synthesis of α-naphthyl functionalized acetates via C-C bond construction under mild reaction conditions and under solvent-free conditions. The light irradiation has been proven to play a pivotal role in the reactions, probably by promoting the generation of active carbene species from α-diazo esters.

Transition metal-free, photocatalytic arylation and deoxygenation for vicinal diketone synthesis using alkynes and arene diazonium salts

A metal-free dioxygenative reaction of aryl diazonium salts with aryl alkynes for vicinal diketone synthesis is developed. The aerobic oxygenation and the organic dye-based photocatalysis constitute the major adavantages of...

Rh(III)-Catalyzed Stereoselective C−H Homoallylation of Indolines with 4-Vinyl-1,3-dioxan-2-ones

An efficient and robust Rh(III)-catalyzed C−H homoallylation of indolines has been developed. Using 4-vinyl-1,3-dioxan-2-one as coupling parnter, a range of homoallylic alcohols could be prepared in excellent stereoselectivities. The current strategy exhibits high efficiency, good yields, and exceptional functional group tolerance.

Thiazole-5-carbaldehyde Synthesis by Cascade Annulation of Enaminones and KSCN with Dess-Martin Periodinane Reagent

The Dess-Martin periodinane (DMP) reagent-mediated reactions of tertiary enaminones with potassium thiocyanate for the synthesis of thiazole-5-carbaldehydes are developed. The product formation involves cascade hydroxyl thiocyanation of the C═C double bond, intramolecular hydroamination of the C≡N bond, and thiazole annulation by condensation on the ketone carbonyl site, representing novel reaction pathways in the reactions between enaminones and thiocyanate salt. DMP plays dual roles in mediating the free radical thiocyanation and inducing the unconventional selective thiazole-5-carbaldehyde formation by masking the in situ generated formyl group during the reaction process.

Visible-Light-Mediated Tandem Difluoromethylation/Cyclization of Alkenyl Aldehydes toward CF2H-Substituted Chroman-4-one Derivatives

An efficient and facile visible-light-mediated tandem difluoromethylation/cyclization of alkenyl aldehydes, with easily accessible and air-stable [Ph₃PCF₂H]⁺Br^- as the difluoromethylation reagent, has been established. A range of CF₂H-substituted chroman-4-one skeletons and their derivatives, such as 2,3-dihydroquinolin-4(1H)-ones, chroman, 3,4-dihydronaphthalen-1(2H)-one, 2,3-dihydrobenzofuran, and 2,3-dihydro-1H-inden-1-one, are efficiently produced in moderate to good yields with excellent chemoselectivity under mild reaction conditions.

Metal-free three-component assemblies of anilines, α-keto acids and alkyl lactates for quinoline synthesis and their anti-inflammatory activity

A new and metal-free three-component method for the synthesis of 2,4-disubstituted quinolines via the reactions of anilines, α-keto acids and alkyl lactates is reported. The reactions proceed in the presence of p-toluene sulfonic acid (p-TSA) and tert-butyl peroxybenzoate (TBPB) to provide diverse quinoline products via the construction of new CC double, C-C single and CN double bonds without producing any organic mass-based side product. Notably, the anti-inflammatory activity of the quinolines has been investigated by measuring their ability to inhibit NO release by lipopolysaccharide (LPS) induced RAW264.7 cells, leading to the identification of 4i, 4t and 4x as potent anti-inflammatory compounds in vitro.

Ultrasound-Promoted Synthesis of α-Thiocyanoketones via Enaminone C═C Bond Cleavage and Tunable One-Pot Access to 4-Aryl-2-aminothiazoles

Ultrasound has been successfully employed to promote the thiocyanation of the C═C bond in enaminones for the synthesis of α-thiocyanoketones and 2-aminothiazoles. The reactions of enaminones with ammonium thiocyanate provide α-thiocyanoketones with ultrasound irradiation at room temperature. More interestingly, simply further heating the vessel after ultrasonic irradiation leads to the selective synthesis of 2-aminothiazoles with an unconventional 4-aryl substructure.

Rh-Catalyzed [4 + 2] Annulation with a Removable Monodentate Structure toward Iminopyranes and Pyranones by C-H Annulation

The Rh-catalyzed reactions of N-pyridinyl enaminones with internal alkynes leading to the synthesis of iminopyranes via a key C-H bond activation and subsequent tautomeric O-H bond cleavage are reported. Moreover, the pyridine ring in the amino group acts as an auxiliary monodentate site for this annulation and can be easily removed by a simple hydrolysis to afford pyranones.

Transition-metal-free three-component coupling approach to QUINAP derivatives

The aluminum(III) triflate catalyzed three-component coupling reaction of alkynes, amines and phosphorylated aryl aldehydes to access phosphoryl quinoline derivatives has been developed. The reaction proceeds in a simple system without the use of transition metals, ligands or additives, thus making it attractive for the fast preparation of a variety of new potential N-P bidentate ligands.

Copper-Catalyzed Regiospecific Amination of Heteroarenes with Quinoneimides

In this work, an unprecedented and widely applicable strategy for the regioselective C-3 amination of indoles and C-2 amination of heteroarenes (pyrrole and benzofuran) is presented in a simple, high-efficiency way. This protocol is also one of the few methods for the efficient construction of C-N bonds of quinoneimides by the 1,6-addition reaction.

Base-Promoted Annulative Difluoromethylenation of Enaminones with BrCF2CO2Et toward 2,2-Difluorinated 2,3-Dihydrofurans

A practical method for the synthesis of 2,2-difluorinated 2,3-dihydrofurans has been established via the [4 + 1] annulation of enaminones and BrCF₂CO₂Et with Na₂CO₃ promotion. This new protocol does not employ any transition metal reagent and enables the annulative difluoromethylation by the partial cleavage of the C═C double bond. In addition, the further treatment with hydrochloric acid in one pot leads to β-keto enoic acids (4-oxo-2-butenoic acids) via a formal enaminone C-N carboxylation.

Visible-light-mediated tandem phosphorylation/cyclization for the synthesis of phosphorylated oxindoles

The visible-light-mediated tandem phosphorylation/cyclization of N-arylacrylamides with H-phosphine oxides has been developed for the synthesis of phosphorylated oxindoles. This efficient and facile process was useful for the construction of a C-P bond and triggered the formation of a C-C bond with good compatibility with functional groups undermild reaction conditions.

Copper-catalyzed C-H/N-H annulation of enaminones and alkynyl esters for densely substituted pyrrole synthesis

Herein, the copper-catalyzed annulation of enaminones with alkynyl esters for the facile synthesis of different pyrroles with a 2,3,4,5-tetrasubstituted structure has been developed. With Cu(OAc)₂ as the only catalyst, the tunable synthesis of 2-vinyl and 2,3-dicarboxyl-functionalized pyrroles has been achieved by using terminal and internal alkynyl esters, respectively. The synthesis of 2-vinyl pyrroles represents the first example accessing 2-vinyl substituted pyrroles via direct cascade reactions involving vinylation and pyrrole ring formation.

Recent advances in transition metal-free annulation toward heterocycle diversity based on the C-N bond cleavage of enaminone platform

The enaminones and analogous stable enamines are well known as platform building blocks in organic synthesis for construction of heterocyclic compounds, especially N-heterocycles. To date, especially enaminones have been successfully...

DMSO as a C1 Source for [2 + 2 + 1] Pyrazole Ring Construction via Metal-Free Annulation with Enaminones and Hydrazines

A cascade reaction between enaminones, hydrazines, and dimethyl sulfoxide (DMSO) for the synthesis of 1,4-disubstituted pyrazoles catalyzed by molecular iodine in the presence of Selectfluor has been realized. DMSO plays a dual role as the C₁ source and the reaction medium. In addition, the synthesis of 1,3,4-trisubstituted pyrazoles using aldehydes as alternative C₁ building blocks has also been achieved.

Synthesis of 3,3-Dihalogenated 2-Aminochromanones via Tandem Dihalogenation and Cyclization of o-Hydroxyarylenaminones with NXS (X = Cl or Br)

An unprecedented method for the synthesis of dichlorinated and dibrominated 2-amino-substituted chromanones is developed by employing enaminones and NCS/NBS as starting materials under microwave irradiation. The reactions proceed quickly to deliver products without using any catalyst or additive, thus providing practical access to 3,3-dihalogenated 2-aminochromanones.

Metal-free enaminone C-N bond cyanation for the stereoselective synthesis of (E)- and (Z)-β-cyano enones

A highly practical method for C-CN bond formation by C-N bond cleavage on enaminones leading to the efficient synthesis of β-cyano enones is developed. The reactions take place efficiently to provide (E)-β-cyano enones with only a molecular iodine catalyst. In addition, the additional employment of oxalic acid enables the selective synthesis of (Z)-β-cyano enones.

Electrochemical C-H Halogenations of Enaminones and Electron-Rich Arenes with Sodium Halide (NaX) as Halogen Source for the Synthesis of 3-Halochromones and Haloarenes

Without employing an external oxidant, the simple synthesis of 3-halochromones and various halogenated electron-rich arenes has been realized with electrode oxidation by employing the simplest sodium halide (NaX, X = Cl, Br, I) as halogen source. This electrochemical method is advantageous for the simple and mild room temperature operation, environmental friendliness as well as broad substrate scope in both C-H bond donor and halogen source components.

Copper-Catalyzed Enaminone C(sp2)-N Bond Phosphonation for Stereoselective Synthesis of Alkenylphosphonates

A direct enaminone C-N bond coupling functionalization that generates a new C-P bond using dialkyl phosphonate for the efficient and stereoselective synthesis of (E)-alkenylphosphonates is reported. The reactions toward target products proceed well with a broad scope, disclosing a valuable new synthetic application of enaminones by the interesting C(sp²)-N bond elaboration.

Tunable Trifunctionalization of Tertiary Enaminones for the Regioselective and Metal-Free Synthesis of Discrete and Proximal Phosphoryl Nitriles

This paper reports an unprecedented trifunctionalization of tertiary enaminones for the synthesis phosphoryl nitriles by the reactions of enaminones with diarylphosphine oxides and trimethylsilyl cyanide (TMSCN) without the use of any metal reagent. Employing tetrabutyl ammonium hydroxide (TBAH) as the catalyst (0.2 equiv) enables discrete cyanophosphonation. On the other hand, selective proximal cyanophosphonation has been realized in the presence of acetic acid only (AcOH).

Pd-Catalyzed Triple-Fold C(sp2)-H Activation with Enaminones and Alkenes for Pyrrole Synthesis via Hydrogen Evolution

The synthesis of NH-free pyrroles via Pd-catalyzed annulation of enaminones and alkenes is reported. With the catalysis of Pd(II), the activation of triple C(sp²)-H bonds, including one internal C(sp²)-H bond in enaminone, has been activated to provide various pyrroles. The interesting evolution of hydrogen gas from the reactions has been observed by a hydrogen detector.

Scissoring Enaminone C═C Double Bond by Free Radical Process for the Synthesis of α-Trifluoromethyl Ketones with CF3SO2Na

The C═C double bond cleavage on tertiary enaminones, enabling the formation of a new C-CF₃ bond, has been realized as a practical method for the synthesis of α-trifluoromethyl ketones with only the promotion of TBHP and ambient heating. Control experiments support that the reactions proceed via a featured free radical process. The deuterium labeling experiment employing D₂O indicates that water participated in the product formation by donating the hydrogen atom for the newly generated α-C-H bond in the product.

Synthesis of 3-halochromones with simple KX halogen sources enabled by in situ halide oxidation

An in situ oxidation strategy for generating molecular halogen has been developed for the synthesis of 3-halochromones by employing simple potassium halides as halogen sources.

Toward C2-nitrogenated chromones by copper-catalyzed β-C(sp2)–H N-heteroarylation of enaminones

The synthesis of C2-nitrogenated chromones has been performed via reactions of enaminones and nitrogen nucleophiles based on an unconventional β-C–H bond functionalization and a featured chromone annulation of enaminones.