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The C-F bond cleavage and C-C bond formation (i.e., carbodefluorination) of readily accessible (per)fluoroalkyl groups constitutes an atom-economical and efficient route to partially fluorinated compounds. However, the selective mono-carbodefluorination of trifluoromethyl (CF 3 ) groups remains a challenge, due to the notorious inertness of C-F bond and the risk of over-defluorination arising from C-F bond strength decrease as the defluorination proceeds. Herein, we report a carbene-initiated rearrangement strategy for the carbodefluorination of fluoroalkyl ketones with β,γ-unsaturated alcohols to provide skeletally and functionally diverse α-mono- and α,α-difluoro-γ,δ-unsaturated ketones. The reaction starts with the formation of silver carbenes from fluoroalkyl N-triftosylhydrazones, followed by nucleophilic attack of a β,γ-unsaturated alcohol to form key silver-coordinated oxonium ylide intermediates, which triggers selective C-F bond cleavage by HF elimination and C-C bond formation through Claisen rearrangement of in situ generated difluorovinyl ether. The origin of chemoselectivity and the reaction mechanism are determined by experimental and DFT calculations. Collectively, this strategy by an intramolecular cascade process offers significant advances over existing stepwise strategies in terms of selectivity, efficiency, functional group tolerance, etc., (© 2022. The Author(s).)

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 2H-pyrazines. The cyclization reactions feature a broad substrate scope, good functional group tolerance, high reaction efficiency, and good to high product yields., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new silver-catalyzed heteroaromatization of propargylic alcohols with p-toluenesulfonylmethyl isocyanide (TosMIC) has been developed that provides an efficient and modular approach to sulfonyl benzoheteroles. For the first time, TosMIC plays a dual role in one reaction: sulfonyl source and ligand. An unprecedented deoxysulfonylation/hydration/condensation reaction pathway is disclosed.

Divergent syntheses of indolizines and 2,4-disubstituted pyrroles by the silver-catalyzed cyclization of 2-pyridyl alkynyl carbinols with isocyanides are reported. These methods provide an effective route to highly functionalized indolizines and 2,4-disubstituted pyrroles in good to excellent yields. The 2,4-disubstituted pyrroles are synthesized by an unprecedented regioselective [3+2] cycloaddition of terminal alkynes with isocyanides.

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]

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]

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]

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]

A silver‐catalyzed cycloaromatization of 1‐(2‐ethynyl‐phenyl)‐prop‐2‐yn‐1‐ol with isocyanides efficiently provides benzo[b]fluorene and benzofuran‐pyrrole derivatives through a modular cascade reaction that includes a nucleophilic attack on the diyne substrate. A C−C cross‐coupling/oxygen transportation/Diels‐Alder/hydrogen shift/isomerization cascade mechanistic pathway is proposed. [ABSTRACT FROM AUTHOR]

Abstract: [3+1+1] annulation of isocyanoacetates with nitrosoarenes for the preparation of 1,4,5‐trisubstituted imidazoles or 4,5‐dihydro‐1H‐imidazoles has been disclosed. Isocyanoacetates serve as both a three‐atom component and a one‐carbon unit in the reaction. Specially, with catalytic amounts of Ag2CO3 and a reduced temperature this [3+1+1] annulation of isocyanoacetates enables the formation of trans‐imidazolines in good yield and with high diastereoselectivity. Silver plays a critical dual role: i) as the catalyst for the efficiency to activate the isocyanides and ii) the oxidant in aromatization process. [ABSTRACT FROM AUTHOR]

The [2+1] cycloaddition of alkynes with diazo compounds represents one of the most powerful and reliable methods for the construction of cyclopropenes. However, it remains a formidable challenge to accomplish the cyclopropenation of alkynes with non-stabilized diazoalkanes, owing to the fact that such compounds are unstable and prone to detonation. Herein, we report a general silver-catalyzed cyclopropenation reaction of alkynes with unstable diazoalkanes, by for the first time the discovery and application of N-nosylhydrazones as room-temperature decomposiable diazo surrogates. This method allows for the efficient assembly a wide variety of cyclopropene derivatives that are otherwise difficult to access by conventional methods. [ABSTRACT FROM AUTHOR]

Silver(i)-promoted carbene insertion into X–H (X = Si, Sn, and Ge) bonds has been realized by using unstable diazo compounds, which are generated in situ from N-nosylhydrazones as carbene precursors. The reaction tolerates a wide range of functional groups and delivers a number of valuable silicon-containing compounds in very high yields (up to 96%). Moreover, organostannanes and organogermanes were as well effectively obtained in very good yields under optimal conditions. [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]

Imidazole ring is an important five-membered aromatic heterocycle that is widely present in natural products and synthetic molecules. The isocyanide-isocyanide [3+2] cross-cycloaddition reaction constitutes a straightforward method to access imidazoles starting from the easily available chemicals. So far, only three successive reports are known and all lead to the formation of 1,4-disubstituted imidazoles. Here, we report the first isocyanide-isocyanide [3+2] cross-cycloaddition reaction allowing for the formation of 1,4,5-trisubstituted imidazoles under silver catalysis. An unexpected 1,2-migration of sulfonyl, alkoxycaybonyl, and carbamoyl groups took place during the cyclization process that is responsible for the formation of trisubstituted imidazoles. This report displayed a mechanistically novel synthetic method toward a variety of imidazole derivatives, which are otherwise difficult to access by conventional methods. [ABSTRACT FROM AUTHOR]

Isocyanides are versatile building blocks, and have been extensively exploited in CH functionalization reactions. However, transition-metal-catalyzed direct CH functionalization reactions with isocyanides suffer from over-insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross-coupling of isocyanides with active methylene compounds through silver-catalysis. The method solves the over-insertion issue and affords a variety of otherwise difficult to synthesize β-aminoenones and tricarbonylmethanes under base- and ligand-free conditions. This report presents a new fundamental CC bond-forming reaction of two basic chemicals. [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]

The article presents a study on silver-catalyzed isocyanide-alkyne cycloaddition which is a practical method to oligosubstituted pyrroles. It states that the transition-metal-catalyzed cycloaddition of isocyanides with unactivated terminal alkynes has been completed. It mentions that the functional-group tolerance, high reaction efficiencies, and high product yields, the silver-catalyzed isocyanide-alkyne cycloaddition can be expected to search for broad synthetic applications.

The front cover image, provided by Xihe Bi, illustrates the comprehensive and critical review of silver ‐ based radical reactions, which especially emphasizes reactivity, selectivity and mechanism. The material is organized according to the type of radicals generated in situ, including carbon ‐ centered radicals and heteroatom ‐ centered radicals, such as nitrogen, oxygen, phosphorus, and sulfur radicals. In each section the authors present the radical generation and their use in organic synthesis through oxidation, addition, coupling, radical cascades, etc. The detailed comparison and analysis allow an understanding of the role and catalytic cycle of silver salts in triggering and promoting the radical reactions, which should stimulate further research interest in the field. Details can be found in the review on pages 1422 – 1502 (G. Fang, X. Cong, G. Zanoni, Q. Liu, X. Bi, Adv. Synth. Catal. 2017, 359, 1422 – 1502; DOI 10.1002/adsc.201601179). [ABSTRACT FROM AUTHOR]

N‐Nosylhydrazones were discovered as the first generation of room‐temperature decomposable diazo surrogates, which led to the development of silver‐catalyzed [2+1] cyclopropenation of alkynes with unstable diazoalkanes. More information can be found in the Communication by X. Bi et al. on page 4756 ff. [ABSTRACT FROM AUTHOR]

1,4,5 ‐ Trisubstituted imidazoles are prepared by the first silver ‐ catalyzed isocyanide–isocyanide [3+2] cycloaddition reaction. A key 1,2 ‐ group migration step enables the formation of functionalized imidazoles that are otherwise difficult to be access. More information can be found in the Communication by Xihe Bi et al. on page   2841 in Issue 20, 2016 (DOI: 10.1002/asia.201601024). [ABSTRACT FROM AUTHOR]