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The majority reactions of alkynes in the literature are reported to proceed via either structural σ-activation or catalytic π-activation of C≡C bonds. We skillfully designed novel methods for the catalytic σ-activation of C≡C bonds of alkynyl compounds. For terminal alkynyl compounds, σ-activation was achieved by silver(i)-catalyzed C–H functionalization. Whereas σ-activation of internal alkynes was accomplished by the generation of propargylic cations from propargylic alcohols under Lewis-acid catalysis. These σ-activated species have been successfully used for new C–C and C–heteroatom bond formation reactions. Plausible reaction pathways were proposed based on typical control experiments to help the readers to gain insights into reactions and for further discovery of new reactions based on this concept of catalytic σ-activation of C≡C bonds. [ABSTRACT FROM AUTHOR]

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon–carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010–2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C–C, C–N, C–O, C–Halo, C–P and C–B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions. [ABSTRACT FROM AUTHOR]

Keywords: catalysis; ligands; organic synthesis; silver; valorization EN catalysis ligands organic synthesis silver valorization 3200 3201 2 07/30/21 20210721 NES 210721 B Silver for the winner b ! GLO:BDBK/21jul21:cctc202100419-toc-0001.jpg PHOTO (COLOR): . gl Although they have long been considered inert in organic synthesis, silver catalysts started to emerge in the literature since the early 2000s and have now become a powerful tool for synthetic chemistry.[1,2] This lagging in silver-catalysis could be attributed mainly to the distinct reactivity profiles arising from the unique electronic and geometrical features of silver catalysts as compared to other transition metal catalysts. Complete switches of reaction products have been achieved by resulting to silver catalysts over other transition-metal catalysts or by fine-tuning the silver-ligand ratio, ligand libraries, counterions or the coordination geometry of the silver catalyst itself. [Extracted from the article]

Aldehyde Termination: A novel copper‐catalyzed transformation from methyl ketones into aldehydes has been accomplished. This method is applicable to a wide range of aromatic and aliphatic methyl ketones and chemoselectively produces aldehydes, accompanied by the release of hydrogen (H2) and carbon dioxide (CO2) as by‐products. [ABSTRACT FROM AUTHOR]

Bis zum Aldehyd: Eine kupferkatalysierte Umsetzung von Methylketonen zu Aldehyden wurde entwickelt. Die Methode kann für eine Vielzahl aromatischer und aliphatischer Methylketone verwendet werden und führt chemoselektiv zu Aldehyden, wobei lediglich Wasserstoff (H2) und Kohlendioxid (CO2) als Beiprodukte entstehen. [ABSTRACT FROM AUTHOR]

Cu2O as the catalyst in water was found to be quite robust for the azide-alkyne cycloaddition (AAC) reaction, which was verified by a wide variety of applicable azides and alkynes. Water was proved to play an essential role because of a significant rate acceleration compared with reactions using organic solvents and conducted under neat conditions. The high catalytic performance of Cu2O/H2O system was further argued by decreasing the catalyst loading to ppm levels. [ABSTRACT FROM AUTHOR]

Cu2O as the catalyst in water was found to be quite robust for the azide-alkyne cycloaddition (AAC) reaction, which was verified by a wide variety of applicable azides and alkynes. Water was proved to play an essential role because of a significant rate acceleration compared with reactions using organic solvents and conducted under neat conditions. The high catalytic performance of Cu2O/H2O system was further argued by decreasing the catalyst loading to ppm levels. [ABSTRACT FROM AUTHOR]

The skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N‐triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon‐atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α‐ or γ‐selective C−H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3‐containing N‐heterocyclic frameworks, such as 2,5‐dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate‐ or catalyst‐controlled chemo‐ and regioselectivity as well as the reaction mechanism. [ABSTRACT FROM AUTHOR]

The skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N‐triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon‐atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α‐ or γ‐selective C−H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3‐containing N‐heterocyclic frameworks, such as 2,5‐dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate‐ or catalyst‐controlled chemo‐ and regioselectivity as well as the reaction mechanism. [ABSTRACT FROM AUTHOR]

Comprehensive Summary Over the past few decades, N‐sulfonyl hydrazones have been recognized as alternative precursors for hazardous diazo compounds in organic synthesis, allowing for diverse innovative and original chemical transformations that were otherwise difficult to achieve. This critical review summarizes the major advancements in the carbene chemistry of N‐sulfonyl hydrazones. The contents of this review are organized based on research conducted by leading scientists who have made significant contributions to this field. The individual carbene transfer reactions and their mechanisms, as well as the potential applications in the synthesis of natural products and complex bioactive molecules, are thoroughly discussed. [ABSTRACT FROM AUTHOR]

A novel copper-catalyzed formal O–H insertion of α-diazo-1,3-dicarbonyl compounds to carboxylic acids has been developed, providing a straightforward synthetic method for α-acyloxy-1,3-dicarbonyl compounds, in which the activation of carboxylic acids by isocyanide plays a crucial role. [ABSTRACT FROM AUTHOR]

A novel Cu(ii)-catalyzed cyclization of α-diazo-β-oxoamides with amines has been developed, constituting a straightforward method to construct pyrrol-3(2H)-one rings. The intramolecular hydrogen bonding effect in α-diazo-β-oxoamides plays an essential role in this reaction. A plausible reaction mechanism involving divergent generation and subsequent [2 + 3] cyclization of ketene and α-diazoimine intermediates was proposed. [ABSTRACT FROM AUTHOR]

A highly efficient iron-catalyzed approach to polysubstituted pyrroles has been developed through the [4C+1N] cyclization of 4-acetylenic ketones with primary amines, leading to the synthesis of a variety of tetra- and fully-substituted pyrroles as well as fused pyrrole derivatives in good to excellent yields. [ABSTRACT FROM AUTHOR]

Azetidines, being four‐membered N‐heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh‐catalyzed one‐carbon ring expansion of aziridines with vinyl‐N‐triftosylhydrazones is presented, which facilitates the synthesis of high value‐added 2‐alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one‐pot two‐step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step‐economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Pharmacological properties of a bioactive molecule can be improved significantly by placing a fluoroalkyl group on its scaffold. However, direct stitching of fluoroalkyl groups to aromatic compounds via C−H bond activation or insertion reaction is a difficult task, thus challenging and of high demand. Herein, an alternative to the Friedel‐Crafts alkylation, we describe an uncharted strategy for selective and efficient trifluoroethylation of indole that relies on iron(III)‐catalyzed C−H activation of aromatic compounds and proceeds via Fe(III)‐carbene insertion into C(sp2)−H bond of indole using trifluoroacetaldehyde N‐triftosylhydrazone as a carbene precursor and FeTPPCl as catalyst. [ABSTRACT FROM AUTHOR]

Azetidines, being four‐membered N‐heterocycles, possess significant potential in contemporary medicinal chemistry owing to their favorable pharmacokinetic properties. Regrettably, the incorporation of functionalized azetidines into pharmaceutical lead structures has been impeded by the absence of efficient synthetic methods for their synthesis. In this study, a Rh‐catalyzed one‐carbon ring expansion of aziridines with vinyl‐N‐triftosylhydrazones is presented, which facilitates the synthesis of high value‐added 2‐alkenyl azetidine products. This research represents the first example of ring expansion of aziridines enabled by vinyl carbenes. Additionally, a one‐pot two‐step protocol, initiated from cinnamaldehyde, was successfully achieved, offering a step‐economical and facile approach for the synthesis of these compounds. The pivotal aspect of this successful transformation lies in the in situ formation of an alkenyl aziridinium ylide intermediate. Experimental investigations, coupled with computational studies, suggest that a diradical pathway is involved in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Given the prevalence of heterocyclic scaffolds in drug‐related molecules, converting these highly modular heterocyclic scaffolds into structural diversified and dearomatized analogs is an ideal strategy for improving their physicochemical and pharmacokinetic properties. Here, we described an efficient method for silver carbene‐mediated dearomative N−N bond cleavage leading to skeletal hopping between indazole and 1,2‐dihydroquinazoline via a highly selective single‐carbon insertion procedure. Using this methodology, a series of dihydroquinazoline analogues with diarylmethylene‐substituted quaternary carbon centers were constructed with excellent yields and good functional group compatibility, which was further illustrated by the late‐stage diversification of important pharmaceutically active ingredients. DFT calculations indicated that the silver catalyst not only induces the formation of the silver carbene, but also activates the diazahexatriene intermediate, which plays a crucial role in the formation of the C−N bond. [ABSTRACT FROM AUTHOR]

The skeletal ring expansion of heteroarenes through carbene insertion is gaining popularity in synthetic chemistry. Efficient strategies for heterocyclic ring expansion to access heterocycles containing a fluoroalkyl quaternary carbon center through fluoroalkyl carbene insertion are highly desirable because of their broad applications in medicinal chemistry. Herein, we report a general strategy for the dearomative one‐carbon insertion of azoles using fluoroalkyl N‐triftosylhydrazones as fluoroalkyl carbene precursors, resulting in ring‐expanded heterocycles in excellent yields with good functional‐group compatibility. The broad generality of this methodology in the late‐stage diversification of pharmaceutically interesting bioactive molecules and versatile transformations of the products has been demonstrated. [ABSTRACT FROM AUTHOR]

The skeletal ring expansion of heteroarenes through carbene insertion is gaining popularity in synthetic chemistry. Efficient strategies for heterocyclic ring expansion to access heterocycles containing a fluoroalkyl quaternary carbon center through fluoroalkyl carbene insertion are highly desirable because of their broad applications in medicinal chemistry. Herein, we report a general strategy for the dearomative one‐carbon insertion of azoles using fluoroalkyl N‐triftosylhydrazones as fluoroalkyl carbene precursors, resulting in ring‐expanded heterocycles in excellent yields with good functional‐group compatibility. The broad generality of this methodology in the late‐stage diversification of pharmaceutically interesting bioactive molecules and versatile transformations of the products has been demonstrated. [ABSTRACT FROM AUTHOR]

A silver‐catalyzed regioselective defluorinative 1,3‐dienylation of trifluoromethyl phenyl N‐triftosylhydrazones using homoallenols as 1,3‐dienyl sources provides a variety of α‐(di)fluoro‐β‐vinyl allyl ketones with excellent functional group tolerance in moderate to good yields. The reaction proceeds through a silver carbene‐initiated sequential etherification and Claisen type [3,3]‐sigmatropic rearrangement cascade. The synthetic utility of this protocol was demonstrated through the downstream synthetic elaboration toward diverse synthetically useful building blocks. [ABSTRACT FROM AUTHOR]

Review: [76 refs. [ABSTRACT FROM AUTHOR]

Review: [348 refs. [ABSTRACT FROM AUTHOR]

(Hetero)arenes continue to prove their indispensability in pharmaceuticals, materials science, and synthetic chemistry. As such, the controllable modification of biologically significant (hetero)arenes towards diverse more‐potent complex molecular scaffolds through peripheral and skeletal editing has been considered a challenging goal in synthetic organic chemistry. Despite many excellent reviews on peripheral editing (i. e., C−H functionalization) of (hetero)arenes, their skeletal editings via single atom insertion, deletion, or transmutations have received less attention in the review literature. In this review, we systematically summarize the state‐of‐the‐art skeletal editing reactions of (hetero)arenes using carbenes, with a focus on general mechanistic considerations and their applications in natural product syntheses. The potential opportunities and inherent challenges encountered while developing these strategies are also highlighted. [ABSTRACT FROM AUTHOR]

The article presents chemical equations for the article "A Copper-Catalyzed Formal O-H Insertion Reaction of ɑ-Diazo-1,3-dicarbonyl Compounds to Carboxylic Acids with the Assistance of Isocyanide" by Z. Wang and others, published in the periodical "Chemical Communications" in 2014.

A wide range of aromatic methyl ketones as well as aliphatic methyl ketones are subjected to the copper-catalyzed oxidative cleavage of the C(CO)-C(CH3) bond to yield the corresponding aldehydes.The oxidation terminates at the aldehyde stage and can be considered as an unprecedented dehydrogenation of saturated aliphatics. [ABSTRACT FROM AUTHOR]

The selective oxidative cleavage of CC σ‐bonds is a great challenge in chemistry and biology. In their Communication on page 11303 ff., X. Bi, Q. Liu, and co‐workers describe a novel method for the oxidative C(CO)C(α) bond cleavage of ketones that completely terminates at the aldehyde stage. A wide range of aromatic and aliphatic methyl ketones could be transformed into aldehydes with a copper catalyst under an oxygen atmosphere, along with the release of H2 and CO2 as the by‐products. [ABSTRACT FROM AUTHOR]

Die selektive oxidative Spaltung von C ‐ C ‐ σ ‐ Bindungen ist eine große Herausforderung für Chemie und Biologie. X. Bi, Q. Liu und Mitarbeiter beschreiben in ihrer Zuschrift auf S. 11513 ff. eine neue Methode für die oxidative Spaltung der C(CO) ‐ C(α) ‐ Bindung von Ketonen, die auf der Stufe des Aldehyds anhält. Ein breites Spektrum aromatischer und aliphatischer Methylketone wurde mithilfe eines Kupferkatalysators unter einer Sauerstoffatmosphäre in die Aldehyde umgewandelt, wobei H2 und CO2 als weitere Produkte entstanden. [ABSTRACT FROM AUTHOR]

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid–liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides. [ABSTRACT FROM AUTHOR]

Review: 303 refs. [ABSTRACT FROM AUTHOR]

The regiochemical course of the ring transformation of semicyclic β-aminoenones (I) with methylhydrazine (II) is shown to be solvent-controlled. [ABSTRACT FROM AUTHOR]

A convenient synthetic procedure is elaborated for the preparation of triazoles (III), (V), and (VI) by Wolff cyclocondensation reactions. [ABSTRACT FROM AUTHOR]

The combined chemistry of silver and isocyanides is unique in performance, proved with the number of recent achievements. With the aim of triggering further research in this field, this review assembles and comprehensively summarizes the silver-based reactions of isocyanides. In this review, we especially emphasize the uniqueness of silver catalysis in the activation of isocyanides, the reaction selectivity, and the mechanistic description. [ABSTRACT FROM AUTHOR]

The first cyclization reaction between vinyl azides and N-sulfonyl-1,2,3-triazoles is reported. A Rh/Ag binary metal catalyst system proved to be necessary for the successful cyclization. By varying the structure of vinyl azides, such reaction allows the divergent synthesis of pyrroles and 2 H-pyrazines. The cyclization reactions feature a broad substrate scope, good functional group tolerance, high reaction efficiency, and good to high product yields. [ABSTRACT FROM AUTHOR]

The construction of allylic quaternary sp3‐carbon centers has long been a formidable challenge in transition‐metal‐catalyzed alkyl‐allyl coupling reactions due to the severe steric hindrance. Herein, we report an effective carbene strategy that employs well‐defined vinyl‐N‐triftosylhydrazones as a versatile allylating reagent to enable direct assembly of these medicinally desirable structural elements from low‐cost alkane feedstocks. The reaction exhibited excellent site selectivity for tertiary C−H bonds, broad scope (>60 examples and >20 : 1:0 r. r.) and good efficiency, even on a gram‐scale, making it a convenient alternative to the well‐known Trost–Tsuji allylation reaction for the formation of alkyl–allyl bonds. Combined experimental and computational studies were employed to unravel the mechanism and origin of site‐ and chemoselectivity of the reaction. [ABSTRACT FROM AUTHOR]

The construction of allylic quaternary sp3‐carbon centers has long been a formidable challenge in transition‐metal‐catalyzed alkyl‐allyl coupling reactions due to the severe steric hindrance. Herein, we report an effective carbene strategy that employs well‐defined vinyl‐N‐triftosylhydrazones as a versatile allylating reagent to enable direct assembly of these medicinally desirable structural elements from low‐cost alkane feedstocks. The reaction exhibited excellent site selectivity for tertiary C−H bonds, broad scope (>60 examples and >20 : 1:0 r. r.) and good efficiency, even on a gram‐scale, making it a convenient alternative to the well‐known Trost–Tsuji allylation reaction for the formation of alkyl–allyl bonds. Combined experimental and computational studies were employed to unravel the mechanism and origin of site‐ and chemoselectivity of the reaction. [ABSTRACT FROM AUTHOR]

A silver‐catalyzed insertion reaction of alkynyl carbenes derived in situ by decomposition of alkynyl N‐nosylhydrazones, into a B−H bond is reported. This protocol emerges as a straightforward synthesis of various propargylic boron compounds with up to 95 % yield. The operationally simple method exhibits high functional group tolerance and produces a variety of propargyl boranes which are synthetically useful building blocks. Deuterium labelling experiment and DFT studies show that the reaction proceeds via insertion of alkynyl Ag‐carbene into the B−H bond and generation of silver carbene occurs in the rate‐determining step. [ABSTRACT FROM AUTHOR]

Catalytic carbene transfer reactions are fundamental transformations in modern organic synthesis, which enable direct access to diverse structurally complex molecules. Despite diazo precursors playing a crucial role in catalytic carbene transfer reactions, most reported methodologies take into account only diazoacetates or related compounds. This is primarily because diazoalkanes, unless they contain a resonance stabilizing group, are more susceptible to violent exothermic decomposition. In this feature article, we present an alternative approach to carbene-transfer reactions based on the formation of highly electrophilic silver carbenes from N-sulfonylhydrazones, where the high electrophilicity of silver carbenes stems from the weak interaction between silver and the carbenic carbon. These precursors are readily accessible, stable, and environmentally sustainable. Using the strategy that employs highly electrophilic silver carbenes, it is possible to develop novel intermolecular transformations involving non-stabilized carbenes, including C(sp3)–H insertion, C(sp3)–C(O) insertion, cycloaddition, and defluorinative functionalization. The silver-catalyzed carbene transfer reactions described here have high efficiency, unusual reactivity, exceptional selectivity, and a reaction pathway that differs from typical transition metal-catalyzed reactions. Our research provided fundamental insight into silver carbene chemistry, and we hope to apply this mode of catalysis to other more general transformations, including asymmetric transformations. [ABSTRACT FROM AUTHOR]

Reductive deoxyallenylation of sterically hindered tertiary propargylic alcohols was realized on reaction with 2-nitrobenzenesulfonylhydrazide (NBSH) by the combined use of Lewis and Brønsted acid catalysts. This method features a broad substrate scope, mild reaction conditions, and good functional-group tolerance, and affords various mono-, di-, and trisubstituted allenes in good-to-excellent yields. The synthetic utility of this method was demonstrated by the synthesis of 2 H-chromenes and 1,2-dihydroquinolines. [ABSTRACT FROM AUTHOR]

The direct gem‐difluoroalkenylation of X−H bonds represents the most straightforward approach to access heteroatomic gem‐difluoroalkenes that, as the isostere of the carbonyl group, have great potency in drug discovery. However, the construction of tetrasubstituted heteroatomic gem‐difluoroalkenes by this strategy is still an unsolved problem. Here, we report the first direct X−H bond gem‐difluoroalkenylation of amines and alcohols with trifluoromethyl ketone N‐triftosylhydrazones under silver (for (hetero)aryl hydrazones) or rhodium (for alkyl hydrazones), thereby providing a most powerful method for the synthesis of tetrasubstituted heteroatomic gem‐difluoroalkenes. This method features a broad substrate scope, high product yield, excellent functional group tolerance, and operational simplicity (open air conditions). Moreover, the site‐specific replacement of the carbonyl group with a gem‐difluorovinyl ether bioisostere in drug Trimebutine and the post‐modification of bioactive molecules demonstrates potential use in medicinal research. Finally, the reaction mechanism was investigated by combining experiments and DFT calculations, and disclosed that the key step of HF elimination occurred via five‐membered ring transition state, and the difference in the electrophilicity of Ag‐ and Rh‐carbenes as well as the multiple intermolecular interactions rendered the effectiveness of Rh catalyst selectively for alkyl hydrazones. [ABSTRACT FROM AUTHOR]

Here, a novel method for the stereoselective synthesis of alkynyl cyclopropanes, by the silver-catalyzed alkynylcyclopropanation of alkenes using alkynyl N-nosylhydrazones as alkynyl carbene precursors, is reported. This method provides a straightforward and powerful approach for preparing various alkynyl cyclopropanes in high yield with excellent stereoselectivities. In addition, the practicality of this method was demonstrated by gram-scale synthesis and late-stage modification of bioactive molecules. [ABSTRACT FROM AUTHOR]

Hydrodefluorination is one of the most promising chemical strategies to degrade perfluorochemicals into partially fluorinated compounds. However, controlled progressive hydrodefluorination remains a significant challenge, owing to the decrease in the strength of C−F bonds along with the defluorination. Here we describe a carbene strategy for the sequential (deutero)hydrodefluorination of perfluoroalkyl ketones under rhodium catalysis, allowing for the controllable preparation of difluoroalkyl‐ and monofluoroalkyl ketones from aryl‐ and even alkyl‐substituted perfluoro‐alkyl ketones in high yield with excellent functional group tolerance. The reaction mechanism and the origin of the intriguing chemoselectivity of the reaction were rationalized by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Hydrodefluorination is one of the most promising chemical strategies to degrade perfluorochemicals into partially fluorinated compounds. However, controlled progressive hydrodefluorination remains a significant challenge, owing to the decrease in the strength of C−F bonds along with the defluorination. Here we describe a carbene strategy for the sequential (deutero)hydrodefluorination of perfluoroalkyl ketones under rhodium catalysis, allowing for the controllable preparation of difluoroalkyl‐ and monofluoroalkyl ketones from aryl‐ and even alkyl‐substituted perfluoro‐alkyl ketones in high yield with excellent functional group tolerance. The reaction mechanism and the origin of the intriguing chemoselectivity of the reaction were rationalized by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

A generalhydroazidation of unactivated alkynes using silver catalysisis reported. The reactions of diverse terminal alkynes with trimethylsilylazide (TMS-N3) in the presence of H2O affordedthe corresponding vinyl azides in good to excellent yields. This reactionhas a broad substrate scope, good functional group tolerance, simpleoperation, and high reaction efficiency, thus providing an easy accessto various functionalized vinyl azides. [ABSTRACT FROM AUTHOR]

Fluoroalkyl 1,2,3-triazoles have great potential as medicinal chemistry building blocks. However, only a few synthetic routes to these compounds are currently available. Herein, we report on a novel method to access 5-fluoroalkyl 1,2,3-triazoles from easily prepared bench-stable perfluoroalkyl N-mesylhydrazone (PFHZ-Ms), a reagent that can transform amines to 5 fluoroalkyl 1,2,3-triazoles via defluorinative [4 + 1] annulation. The simple reaction protocol can be applied to a variety of amines containing a range of functional groups, delivering 1,2,3-triazoles in good to excellent yield. The utility of this method was demonstrated in the late-stage modification of bioactive molecules. [ABSTRACT FROM AUTHOR]

The [2+1] cycloaddition reaction of a metal carbene with an alkene can produce important cyclopropane products for synthetic intermediates, materials, and pharmaceutical applications. However, this reaction is often accompanied by side reactions, such as coupling and self‐coupling, so that the yield of the cyclopropanation product of non‐silver transition‐metal carbenes and hindered alkenes is generally lower than 50 %. To solve this problem, the addition of a low concentration of diazo compound (decomposition of sulfonyl hydrazones) to alkenes catalyzed by either CuOAc or PdCl2 was studied, but side reactions could still not be avoided. Interestingly, however, the yield of cyclopropanation products for such hindered alkenes were as high as 99 % with AgOTf as a catalyst. To explain this unexpected phenomenon, reaction pathways have been computed for four different catalysts by using DFT. By combining the results of these calculations with those obtained experimentally, it can be concluded that the efficiency of the silver catalyst is due to the barrierless concerted cycloaddition step and the kinetic inhibition of side reactions by a high concentration of alkene. [ABSTRACT FROM AUTHOR]

• Asymmetric cyclopropanization of benzofuran was achieved in the presence of chiral rhodium catalysts. • Using N -triftosylhydrazones as the safe diazo-compound surrogate, the reaction conditions are mild and safe. • DFT calculations explain the reason behind the high enantioselectivity during this cyclopropanation reaction. An asymmetric dearomative cyclopropanation of benzofuran has been accomplished by a novel catalytic method that relies on using trifluoromethyl N -triftosylhydrazones as carbene sources in the presence of a chiral rhodium catalyst. This reaction produces chiral trifluoromethyl-tethered 2,3-disubstituted benzofuran cyclopropane, which carries versatile pharmacophores 2,3-dihydrobenzofuran and trifluoromethyl-substituted quaternary carbon centers. Notably, this process offers distinct advantages over other existing approaches due to being step-economic and eliminating green-gas N 2 as a harmless coproduct. DFT calculations explain the reason behind the high enantioselectivity during this cyclopropanation reaction. Asymmetric dearomatization of benzofuran was achieved using N -triftosylhydrazones as a carbene source under rhodium catalysis. This efficient asymmetric transformation proceeds under mild and convenient conditions with significant functional group tolerance, providing optically pure benzofuran cyclopropane with a trifluoromethylated quaternary stereocenter. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite the growing importance of volatile functionalized diazoalkanes in organic synthesis, their safe generation and utilization remain a formidable challenge because of their difficult handling along with storage and security issues. In this study, we developed a bench‐stable difluoroacetaldehyde N‐triftosylhydrazone (DFHZ‐Tfs) as an operationally safe diazo surrogate that can release in situ two low‐molecular‐weight diazoalkanes, diazoacetaldehyde (CHOCHN2) or difluorodiazoethane (CF2HCHN2), in a controlled fashion under specific conditions. DFHZ‐Tfs has been successfully employed in the Fe‐catalyzed cyclopropanation and Doyle–Kirmse reactions, thus highlighting the synthetic utility of DFHZ‐Tfs in the efficient construction of molecule frameworks containing CHO or CF2H groups. Moreover, the reaction mechanism for the generation of CHOCHN2 from CF2HCHN2 was elucidated by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Despite the growing importance of volatile functionalized diazoalkanes in organic synthesis, their safe generation and utilization remain a formidable challenge because of their difficult handling along with storage and security issues. In this study, we developed a bench‐stable difluoroacetaldehyde N‐triftosylhydrazone (DFHZ‐Tfs) as an operationally safe diazo surrogate that can release in situ two low‐molecular‐weight diazoalkanes, diazoacetaldehyde (CHOCHN2) or difluorodiazoethane (CF2HCHN2), in a controlled fashion under specific conditions. DFHZ‐Tfs has been successfully employed in the Fe‐catalyzed cyclopropanation and Doyle–Kirmse reactions, thus highlighting the synthetic utility of DFHZ‐Tfs in the efficient construction of molecule frameworks containing CHO or CF2H groups. Moreover, the reaction mechanism for the generation of CHOCHN2 from CF2HCHN2 was elucidated by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

In recent years, radical C–C bond cleavage reactions have been increasingly understood and used to perform transformations that complement traditional ionic processes. However, to date radical C–C bond cleavage/functionalization reactions have not been the subject of a dedicated review. Herein we summarize the most recent and significant developments in the radical activation and functionalization of carbon–carbon bonds, with an emphasis on both synthetic outcomes and reaction mechanisms, and highlight how these radical C–C bond cleavage reactions enable challenging transformations. [ABSTRACT FROM AUTHOR]