Silver-Catalyzed Csp−H and Csp−Si Bond Transformations and Related Processes

Synthesis of Dihalonaphthalenes via Silver-Catalyzed Halogenation and Electrophilic Cyclization of Terminal Alkynols

Herein, we report a silver-catalyzed halogenation and electrophilic cyclization reaction based on the trifunctionalization of terminal alkynols with NBS or iodine monochloride in a step-efficient synthetic way to produce homo/heterodihalogenated naphthalene derivatives bearing two different halogen atoms in moderate to good yields. This methodology readily accommodates various functional groups, including electron-withdrawing nitro, cyano, acid-sensitive dioxazolyl, and alkoxy groups.

Computational Research on Ag(I)-Catalyzed Cubane Rearrangement: Mechanism, Metal and Counteranion Effect, Ligand Engineering, and Post-Transition-State Desymmetrization

Ag(I) salts have demonstrated superior catalytic activity in the cubane-cuneane rearrangement. This research presents a comprehensive mechanistic investigation using high-level computations. The reaction proceeds via oxidative addition (OA) of Ag(I) to the C-C bond, followed by C-Ag bond cleavage and subsequent dynamically concerted carbocation rearrangement. The OA of Ag(I) exhibits significant more electrophilic nature than classical transition metal-induced OA, and the superior catalytic activity of Ag(I) is attributed to the accessibility of a highly electrophilic "bare" Ag+ center and a relatively weak Ag-C bond. However, the highly Lewis acidic nature of the Ag(I) center limits the substrate scope. To address this problem, ligand and counteranion screening was conducted, revealing that chiral biarylether ligands in combination with BF4- as the counteranion offer both enhanced reactivity and improved chemoselectivity while suppressing the Lewis acidity. Additionally, quasi-classical molecular dynamics simulations indicate the possibility of a novel desymmetrization pathway through post-transition-state dynamics in the biarylether-Ag(I)-BF4- system, thereby providing a potential avenue for enantioselective cuneane synthesis.

Access to Conjugated Enynes via Allenyl Silver Formation/Cyclization/Decarboxylation Reaction Catalyzed by Silver Carbonate(I)

Herein, we develop a novel and straightforward access to cyclic conjugated enynes catalyzed by silver carbonate/DBU from readily available substrates with good yields. The reaction is easy to set up, broad in scope, and can also be conducted in a one-pot fashion from easily accessible substrates through a sequence Michael addition reaction/cyclization. Based on our previous works, the mechanism proposed would involve an allenyl silver intermediate and decarboxylation reaction.

AgNTf2-Catalyzed Regioselective C-H Alkenylation of N,N-Dialkylanilines with Ynamides

Regioselective C-H alkenylation of N,N-dialkylanilines with ynamides was developed using AgNTf₂ as a catalyst. This approach represents a facile hydroarylation of ynamides, allowing for the introduction of an alkenyl group exclusively at the para position of aniline derivatives. As a result, a series of 4-alkenyl N,N-dialkylanilines were synthesized with excellent regioselectivities.

Mechanism of Z-Selective Hydroalkylation of Terminal Alkynes

This paper describes a detailed mechanistic study of the silver-catalyzed Z-selective hydroalkylation of terminal alkynes. Considering the established mechanistic paradigms for Z-selective hydroalkylation of alkynes, we explored a mechanism based on the radical carbometalation of alkynes. Experimental results have provided strong evidence against the initially proposed radical mechanism and have led us to propose a new mechanism for the Z-selective hydroalkylation of alkynes based on boronate formation and a 1,2-metalate shift. The new mechanism provides a rationale for the excellent Z-selectivity observed in the reaction. A series of stoichiometric experiments has probed the feasibility of the proposed elementary steps and revealed an additional role of the silver catalyst in the protodeboration of an intermediate. Finally, a series of kinetic measurements, KIE experiments, and competition experiments allowed us to identify the turnover limiting step and the resting state of the catalyst. We believe that the results of this study will be useful in the further exploration and development of related transformations of alkynes.

Fluoride Ion-Initiated Decarboxylation of Silyl Alkynoates to Alkynylsilanes

This communication describes the development of a metal-free catalytic decarboxylation of silyl alkynoates to alkynylsilanes. Treatment of a silyl alkynoate with a catalytic amount of tetrabutylammonium difluorotriphenylsilicate (TBAT) in N,N-dimethylformamide at 150 °C resulted in decarboxylation to give the corresponding alkynylsilane in good to excellent yield (75 → 95%). The TBAT system was applicable to the decarboxylation of sterically demanding silyl alkynoates such as tert-butyldiphenylsilyl 3-phenylpropiolate. Mechanistic studies revealed that the tetrabutylammonium alkynoate derived from TBAT and the silyl alkynoate act as a catalyst for the decarboxylation.

Dissecting transmetalation reactions at the molecular level: C-B versus F-B bond activation in phenyltrifluoroborate silver complexes

The gas-phase unimolecular reactions of the silver(i) complex [Ag(PhBF₃)₂]^-, formed via electrospray ionisation mass spectrometry of solutions containing the phenyltrifluoroborate salt and AgNO₃, are examined. Upon collision induced dissociation (CID) three major reaction channels were observed for [Ag(PhBF₃)₂]^-: Ph^- group transfer via a transmetalation reaction to yield [PhAg(PhBF₃)]^-; F^- transfer to produce [FAg(PhBF₃)]^-; and release of PhBF₃^-. The anionic silver product complexes of these reactions, [LAg(PhBF₃)]^- (where L = Ph and F), were then mass-selected and subjected to a further stage of CID. [PhAg(PhBF₃)]^- undergoes a Ph^- group transfer via transmetalation to yield [Ph₂Ag]^- with loss of BF₃. [FAg(PhBF₃)]^- solely fragments via loss of BF₄^-, a reaction that involves Ph^- group transfer from B to Ag in conjunction with F^- transfer from Ag to B. Density functional theory (DFT) calculations on the various competing pathways reveal that: (i) the overall endothermicities govern the experimentally observed product ion abundances; (ii) the Ph^- group and F^- transfer reactions proceed via late transition states; and (iii) formation of BF₄^- from [FAg(PhBF₃)]^- is a multistep reaction in which Ph^- group transfer from B to Ag proceeds first to produce a [FAgPh(BF₃)]^- complex in which the BF₃ moiety is initially weakly bound to the ipso-carbon of the phenyl group and then migrates across the linear [FAgPh]^- moiety from C to Ag to F yielding [PhAg(BF₄)]^-, which can then dissociate via loss of PhAg.

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.

Mechanistic investigation of zinc-promoted silylation of phenylacetylene and chlorosilane: a combined experimental and computational study

The zinc-promoted silylation method is of great importance to synthesize high-performance silicon-containing arylacetylene (PSA) resins in the industry. However, it is difficult to eliminate the accompanied by-product of terminal alkenes due to the lack of mechanistic understanding of the silylation. The initiation of zinc-promoted silylation is facilitated by the interaction between zinc and phenylacetylene. Our DFT calculations indicated that the intermolecular hydrogen transfer of phenylacetylene follows an ionic pathway, which generates a phenylacetylene anion and the corresponding alkene moieties on the zinc surface. The styrene by-product is observed in this stage, with its alkene moieties desorbing as radicals into the solvent under the high reaction temperature. Three possible intermediates of surface phenylacetylene anions were proposed including PhC[triple bond, length as m-dash]C-Zn, PhC[triple bond, length as m-dash]CZnCl, and (PhC[triple bond, length as m-dash]C)2Zn. These carbanion-zinc intermediates undergo an SN2 reaction with Me3SiCl to afford the alkynylsilane on the zinc surface, which is calculated to be the rate-determining step for the zinc-promoted silylation reaction.

Silver-Catalyzed para-Selective Amination and Aminative Dearomatization of Phenols with Azodicarboxylates in Water

An efficient silver-catalyzed para-selective amination and aminative dearomatization of phenols with azodicarboxylates was developed. It afforded the para-aminophenols or amino cyclohexadieneones from free phenols depending on whether it has a para-substituent. The reaction proceeded smoothly in water under simple and mild conditions, giving the highly selective products in good yields within a short reaction time. It also showed broad substrate scope and good functional group compatibility.

Silver-Catalyzed Activation of Terminal Alkynes for Synthesizing Nitrogen-Containing Molecules

Alkynes are one of the most abundant chemicals in organic chemistry, and therefore the development of catalytic reactions to transform alkynes into other useful functionalities is of great value. In recent decades, extraordinary advances have been made in this area with transition-metal catalysis, and silver-based reagents are ideal for the activation of alkynes. This high reactivity is probably due to the superior π-Lewis acidic, carbophilic behavior of silver(I), allowing it to selectively activate carbon-carbon triple bonds (C≡C) through the formation of a silver-π complex. Within this field, we have been interested in the activation and subsequent reactions of readily accessible terminal alkynes for the synthesis of nitrogen-containing compounds, which has generally received less attention than methods involving internal alkynes. This is possibly due to the lack of suitable reactive reaction partners that are compatible under transition metals. Therefore, a thorough understanding of the factors that influence homogeneous silver catalysis and the identification of the appropriate reaction partners can provide a powerful platform for designing more efficient silver-catalyzed reactions of terminal alkynes. In this context, we envisioned that using readily available, environmentally benign, and inexpensive trimethylsilyl azide (TMSN₃) or an isocyanide as the nitrogen-donor would be the key to develop novel reactions of terminal alkynes.This Account describes our efforts since 2013 toward the development of novel silver-catalyzed tandem reactions of terminal alkynes with either TMSN₃ or isocyanides for the assembly of various nitrogen-containing compounds. The first section of this Account discusses the initial developments in the silver-catalyzed hydroazidation of terminal alkynes with TMSN₃ and the subsequent advances made in our laboratory. We first describe the discovery and experimental and computational mechanistic investigations of silver-catalyzed hydroazidation reactions, which is the most efficient strategy reported to date for accessing vinyl azides. Mechanistic study of this hydroazidation reaction provides an alternative activation mode for terminal alkyne conversion in transition metal catalysis. We then present the chemistry of in situ generated vinyl azides, including one-pot tandem radical addition/cyclization or migration reactions of terminal alkynes to access a variety of nitrogen-containing molecules. Finally, we discuss the one-pot, multistep tandem hydroazidation and 1,2-azide migratory gem-difluorination of terminal alkynes for the synthesis of β-difluorinated alkyl azides. The second section describes the silver-catalyzed coupling reactions between terminal alkynes and isocyanides, which offer a straightforward method for accessing synthetically useful building blocks, such as pyrroles, allenamides, benzofuran, vinyl sulfones, indazolines, propiolonitriles, and pyrazoles. The high efficiency, mild conditions, low cost, broad substrate scope, high chemo- and regioselectivity, step economy, and ecofriendliness of the developed approaches make them attractive and practical. The progress in this area provides guiding principles for designing new reactions of terminal alkynes that can be extended to various nitrogen-containing molecules of interest to medicinal and materials chemists.

Silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes

A simple silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes has been described. This strategy provides an efficient and practical avenue to access various deuterated electron-rich arenes, azaarenes and α-deuterated 2-alkyl azaarenes with good to excellent deuterium incorporation utilizing D₂O as the source of deuterium atoms.

A practical silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes utilizing D₂O as a deuterium source has been developed.

Silver(i)-catalyzed addition of pyridine-N-oxides to alkynes: a practical approach for N-alkenoxypyridinium salts

A smooth catalytic approach to N-alkenoxypyridinium salts by using pyridine-N-oxides as the nucleophilic partner with alkynes under acidic conditions has been developed. This method uses different Ag(i) salts, with 5% AgOAc being the most efficient, to provide an efficient, practical and alternative way to obtain valuable N-alkenoxypyridinium salts with good to excellent yields (up to 93%).

Beyond the traditional roles of Ag in catalysis: the transmetalating ability of organosilver(i) species in Pd-catalysed reactions

The role of silver salts in Pd-catalysed C–C bond forming transformations.

A mineralogically-inspired silver–bismuth hybrid material: an efficient heterogeneous catalyst for the direct synthesis of nitriles from terminal alkynes

A silver-containing hybrid material is reported as an effective heterogeneous catalyst for the direct synthesis of organic nitriles from terminal alkynes.

Substrate-Controlled Product Divergence: Silver-Catalyzed Reaction of Trifluoromethyl Ketones with Terminal Alkynes

A distinct dichotomy in product distribution was initially observed in the silver-catalyzed reaction of trifluoromethyl (CF₃) ketones with terminal alkynes having two different types of electronic natures. The domino reaction smoothly proceeded almost exclusively with high stereoselectivity with terminal alkynes containing ester groups, whereas alkynylation occurred in good yield when terminal alkynes containing aryl or alkyl groups were present. The results indicated that the electronic nature of terminal alkynes can act as a switch that enables either the domino reaction or alkynylation between terminal alkynes and CF₃ ketones.

Silver(I)-Catalyzed Intramolecular Cyclizations of Epoxide-Propargylic Esters to 1,4-Oxazine Derivatives

An interesting silver(I)‐catalyzed, one‐pot intramolecular cyclization of epoxide‐propargylic esters is described. A variety of 1,4‐oxazine derivatives were obtained through a novel domino sequence, including three‐membered ring‐opening, 3,3‐sigmatropic rearrangement, 6‐exo‐cycloisomerization and subsequent intramolecular elimination in moderate yields under mild conditions.