Synthesis of Pyrrole-2-carbaldehyde Derivatives by Oxidative Annulation and Direct Csp3-H to C═O Oxidation

Tandem Synthesis of Polysubstituted Pyrroles via Cu(I)-Catalyzed Cyclization of Ketene N,S-Acetals with β-Ketodinitriles

A new approach to multifunctionalized pyrroles has been explored by the tandem cyclization of α-oxoketene-N,S-acetals with β-ketodinitriles using Cu(MeCN)4BF4 and Ag2CO3 in toluene under reflux conditions. The reaction involves C-C/C-N bond creation, and is assumed to proceed via enamine formation, intramolecular cyclization, and rearrangement. The potential of the methodology has also been demonstrated for a gram-scale reaction as well as for some useful organic transformations. The reaction offers a practical pathway to achieve polysubstituted pyrroles with broad substrate scope and good functional group tolerance.

Molecular-Oxygen-Mediated Multicomponent Oxidative Cyclization: Synthesis of Tertiary-Alcohol-Unit-Bearing N-Heterocycles via Transforming C-H to C-OH Bonds

We developed a molecular-oxygen-mediated multicomponent oxidative cyclization strategy to synthesize N-heterocycles containing tertiary alcohol units via the formation of key C-OH bonds and quaternary carbon centers. This formal [3 + 2 + 1] annulation offers a green and sustainable alternative for the de novo C-OH bond formation, using O2 as both the oxidant and oxygen source under metal- and catalyst-free conditions. Notably, continuous [1,5]-hydrogen transfer together with excess alcohols promotes the formation of C-OH-bearing products. Additionally, the generation of quaternary carbon centers inhibits the conversion of C-OH bonds to C═O bonds, thus stabilizing the desired products.

Cascade [3 + 2] Annulation of 1,3-Dicarbonyl Compounds and Ethyl Secondary Amines for Pyrrole Synthesis via Poly C(sp3)-H Bond Functionalization

The synthesis of polyfunctionalized pyrroles via the cascade reactions of 1,3-dicarbonyl compounds and two molecules of ethyl secondary amines has been realized via simple iodine catalysis in the presence of Dess-Martin periodinane (DMP). The formation of the target pyrrole products involves the formation of one new C-C and two new C-N bonds via the major functionalization of six C(sp3)-H bonds, presenting a highly novel and efficient synthetic protocol toward pyrrole scaffolds.

I2-Mediated [3 + 3] Annulation for the Construction of Indole-Pyrimidine-Pyrazole-Fused Tetracyclic Heteroarenes

An I2-mediated annulation of 3-aminopyrazoles with indole-3-carboxaldehydes has been demonstrated for the first time. This tandem strategy allows the facile construction of indole-pyrimidine-pyrazole-fused tetracyclic heteroarenes that are otherwise inaccessible by the existing methods. These fused heterocycles exhibited enhanced antifungal activities against Valsa mali and Botryosphaeria dothidea compared with commercial Xemium fungicide.

I2-DMSO-Mediated Construction of 2,3- and 2,4-Disubstituted Pyrimido[1,2-b]indazole Skeletons

An efficient synthetic method for constructing 2,3- and 2,4-disubstituted pyrimidio[1,2-b]indazole skeletons through I2-DMSO-mediated and substrate-controlled regioselective [4 + 2] cyclization is reported. The reaction conditions are mild, its operation is simple, and the substrate scope is wide. More than 60 pyrimidio[1,2-b]indazole derivatives have been synthesized, providing a new methodology for constructing related molecules and potentially enriching bioactive-molecule libraries.

The Direct Conversion of Esters to Ketones Enabled by a Traceless Activating Group

We report here the design and development of a method for the single-step conversion of esters to ketones with simple reagents. The selective transformation of esters to ketones, rather than tertiary alcohols, is made possible by the use of a transient sulfinate group on the nucleophile that activates the adjacent carbon toward deprotonation to form a carbanion that adds to the ester, followed by a second deprotonation to prevent further addition. The resulting dianion undergoes spontaneous fragmentation of the SO₂ group upon quenching with water to reveal the ketone product.

Synthesis of Pyrrole via Formal Cycloaddition of Allyl Ketone and Amine under Metal-Free Conditions

A new metal-free synthesis of pyrrole from allyl ketone and amine has been established. The reaction proceeds via an thiolative activation of the C-C double bond with dimethyl(methylthio)sulfonium trifluoromethanesulfonate, followed by a nucleophilic ring-opening addition of primary amine to the generated episulfonium intermediate, and then an internal condensation and aromatization. This mild procedure provides a novel strategy to the construction of substituted pyrroles through a formal [4 + 1] cycloaddition reaction.

Employing Arylacetylene as a Diene Precursor and Dienophile: Synthesis of Quinoline via the Povarov Reaction

A novel I₂-mediated Povarov reaction of arylacetylenes and anilines for the synthesis of 2,4-substituted quinolines has been developed, in which arylacetylene first acts as both a diene precursor and dienophile. This work further develops the Povarov reaction to expand the types of diene precursors. Preliminary mechanistic studies indicate that the I₂/DMSO system realized the oxidative carbonylation of C(sp)-H of arylacetylene and then undergoes a [4 + 2] cycloaddition reaction.

Recent advances in the copper-catalyzed aerobic Csp3-H oxidation strategy

The interplay between copper catalysts and molecular oxygen provides the opportunity to control the promiscuous catalytic behaviors in aerobic Csp3-H bond oxidations without using stoichiometric amounts of oxidants. This mini-review aims to cover the Cu-catalyzed aerobic benzylic and α-carbonyl Csp3-H oxidations and that of the carbon next to an amine group in the past five years. The development of tandem multicomponent reactions employing aerobic Csp3-H bond oxidations will be discussed to highlight the controlled catalyst behaviors and the catalyst interactions between multiple reaction components.

Synthesis of Polysubstituted Pyrroles through Electro-Oxidative Annulation of 1,3-Dicarbonyl Compounds and Primary Amines

Reported herein is a synthetic method of polysubstituted pyrroles from easily available materials, 1,3-dicarbonyl compounds and primary amines, via electro-oxidative intermolecular annulation. Under similar conditions, enamines are also converted smoothly into desired products, indicating that in situ formed enamines are crucial intermediates for the first transformation. Neither transition-metal salts nor harsh conditions are required to facilitate the dehydrocyclization process.

Copper-catalyzed aerobic oxidative domino cyclization of methyl azaarenes with 6-amino-pyrimidine-2,4-diones and pyrazol-5-amines: access to dipyrimidine/dipyrazolo-fused pyridines

An aerobic copper-catalyzed oxidative domino cyclization of methyl azaarenes with 6-amino-pyrimidine-2,4-diones and pyrazol-5-amines for the synthesis of dipyrimidine/dipyrazolo-fused pyridines was reported.

Reactions involving aryl methyl ketone and molecular iodine: a powerful tool in the one-pot synthesis of heterocycles

The preparation of heterocyclic compounds has attracted great attention in organic chemistry because of their extensive application in the field of bioactive molecules, materials science, and natural products.

Iodine-Promoted Multicomponent Synthesis of 2,4-Diamino-1,3,5-triazines

A novel and efficient multicomponent cyclization of methyl ketones, cyanamides, and arylamines for the synthesizing 2,4-diamino-1,3,5-triazines via consecutive formation of four C-N bonds is reported. This multicomponent reaction is characterized by the employment of two molecules of cyanamide for double C(sp³)-H amination of methyl ketones, avoiding complicated prepreparation of substrates and expanding the substrate scope. Furthermore, this multicomponent cyclization strategy provides a new approach for generating diverse 2,4-diamino-1,3,5-triazines with a broad substrate scope under mild conditions.

Synthesis of 2-Formylpyrroles from Pyridinium Iodide Salts

The first I₂-mediated synthesis of 2-formylpyrroles from pyridinium salts is reported. This protocol enables the synthesis of diversely substituted 2-formylpyrroles in good yields under operationally simple conditions. The detailed mechanistic studies reveal that the reaction proceeds via a novel H₂O-triggered ring opening of the pyridinium salt and a subsequent intramolecularly nucleophilic addition sequence.

Design and synthesis of two new steroid derivatives with biological activity on heart failure via the M2-muscarinic receptor activation

Several drugs have been prepared to treat of heart failure using some protocols which require dangerous reagents and specific conditions. The aim of this study was to synthesize a series of steroid derivatives (compounds 2 to 18) using some chemical strategies. The biological activity of steroid derivatives against heart failure was evaluated using an ischemia/reperfusion model. In addition, the effect exerted by compounds 4 or 5 on left ventricular pressure was evaluated in the absence or presence of yohimbine, butaxamine and methoctramine. The results showed that 1) both compounds 4 or 5 significantly decrease the heart failure (translated as infarct area) compared with the compounds 2, 3 and 6-18. In addition, the compound 4 and 5 decreased the left ventricular pressure in a dose-dependent manner and this effect was significantly inhibited in the presence of methoctramine (p = 005). In conclusion, the compounds 4 or 5 decrease both the infarct area and left ventricular pressure via M₂-muscarinic receptor activation.

Recent Progress in the Synthesis of Pyrroles

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Pyrrole derivatives are nitrogen-containing heterocyclic compounds and widely distributed in a large number of natural and non-natural compounds. These compounds possess a broad spectrum of biological activities such as anti-infammatory, antiviral, antitumor, antifungal, and antibacterial activities. Besides their biological activity, pyrrole derivatives have also been applied in various areas such as dyes, conducting polymers, organic semiconductors.

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Due to such a wide range of applicability, access to this class of compounds has attracted intensive research interest. Various established synthetic methods such as Paal-Knorr, Huisgen, and Hantzsch have been modified and improved. In addition, numerous novel methods for pyrrole synthesis have been discovered. This review will focus on considerable studies on the synthesis of pyrroles, which date back from 2014.

DFT investigation on the mechanisms of Csp3–H functionalization of glycine derivatives induced by radical cation salt

The mechanism of Csp³–H functionalization between ethyl 2-(p-tolylamino)acetate and phenylethylene initiated by tris(4-bromophenyl)aminium hexachloroantimonate was elaborated based on DFT calculations.

A transition metal-free approach towards the regioselective synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles

A transition metal-free one-pot sequential approach has been unfolded for the synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles by using highly diverse 1-formyl-9H-β-carbolines as a template.

Iodine-promoted one-pot synthesis of 1,3,4-oxadiazole scaffolds via sp3 C–H functionalization of azaarenes

An efficient metal-free one-pot protocol has been developed for the construction of 1,3,4-oxadiazole derivatives via iodine-mediated oxidative amination of benzylic C–H bonds of azaarenes.

Oxidative C(sp3)–H functionalization of methyl-azaheteroarenes: a facile route to 1,2,4-triazolo[4,3-a]pyridines

An oxidative [4 + 1] annulation for triazolo[4,3-a]pyridine–quinoline linked diheterocycle synthesis via functionalization of the sp³ C–H bonds of 2-methyl-azaheteroarenes has been developed.

Trimethylsilyl-Protected Alkynes as Selective Cross-Coupling Partners in Titanium-Catalyzed [2+2+1] Pyrrole Synthesis

Trimethylsilyl (TMS)-protected alkynes served as selective alkyne cross-coupling partners in titanium-catalyzed [2+2+1] pyrrole synthesis. Reactions of TMS-protected alkynes with internal alkynes and azobenzene under the catalysis of titanium imido complexes yielded pentasubstituted 2-TMS-pyrroles with greater than 90 % selectivity over the other nine possible pyrrole products. The steric and electronic effects of the TMS group were both identified to play key roles in this highly selective pyrrole synthesis. This strategy provides a convenient method to synthesize multisubstituted pyrroles as well as an entry point for further pyrrole diversification through facile modification of the resulting 2-silyl pyrrole products, as demonstrated through a short formal synthesis of the marine natural product lamellarin R.

NaHS·nH2O-induced umpolung: the synthesis of 2-acyl-3-aminoindoles from aryl methyl ketones and 2-aminobenzonitriles

An efficient method for constructing 2-acyl-3-aminoindoles from methyl ketones and 2-aminobenzonitriles is described, in which NaHS·nH₂O is used as a novel umpolung reagent for the first time in organic synthesis.