Highly Regio- and Stereoselective Hydrosilylation of Internal Thioalkynes under Mild Conditions

Regiodivergent Synthesis of 4- and 5-Sulfenyl Oxazoles from Alkynyl Thioethers

The regiodivergent synthesis of 4- and 5-sulfenyl oxazoles from 1,4,2-dioxazoles and alkynyl thioethers has been achieved. Gold-catalysed conditions are used to favour the formation of 5-sulfenyl oxazoles via β-selective attack of the nitrenoid relative to the sulfenyl group. In contrast, 4-sulfenyl oxazoles are formed by α-selective reaction under Brønsted acid conditions from the same substrates. The nature of stabilising gold-sulfur interactions have been investigated by natural bond orbital analysis, showing that the S→Au interactions are significantly stronger in the intermediate that favours the 5-sulfenyl oxazoles. A kinetic survey identifies catalyst inhibition processes. This study into the regiodivergent methods includes the development of telescoped annulation-oxidation protocols for regioselective access to oxazole sulfoxides and sulfones.

Chemo-, regio- and stereoselective access to polysubstituted 1,3-dienes via Nickel-catalyzed four-component reactions

1,2-Difunctionalization of alkynes offers a straightforward approach to access polysubstituted alkenes. However, simultaneous multi-component cascade transformations including difunctionalization of two alkynes with both syn- and anti-selectivity in one catalyst system is undeveloped and proves to be a significant challenge. Herein, we report a Nickel-catalyzed four-component reaction to access polysubstituted 1,3-dienes using two terminal alkynes, aryl boroxines, and perfluoroalkyl iodides, wherein the reaction forms three new C-C bonds in a single vessel and serve as a modular strategy to access polysubstituted 1,3-dienes with excellent chemoselectivity, good regioselectivity and exclusive stereoselectivity. Control experiments reveal the plausible reaction mechanism and DFT calculations explain the cause for the formation of this unusual four-component reaction. Furthermore, we successfully incorporate two biologically active units into 1,2,3,4-tetrasubstituted 1,3-dienes, which greatly increases the diversity of molecular scaffolds and brings more potential values to medicinal chemistry, the synthetic utility of our protocol is further demonstrated by the late-stage transformations.

Lewis Acid-Catalyzed Formal [4 + 2] Reaction of Alkynyl Sulfides and 2-Pyrones To Access Polysubstituted Aryl Sulfides

A practical and efficient method to access polysubstituted aryl sulfides has been discovered via a Lewis acid-catalyzed reaction between alkynyl sulfide and 2-pyrone, involving a Diels-Alder/retro-Diels-Alder pathway. Alkynyl sulfide as an electron-rich dienophile and 2-pyrones as electron-poor dienes are conjunctively transformed into a series of polysubstituted aryl sulfides with broad functional group compatibility in good to excellent yields (40 examples, 43-88% yield). The robustness and practicality of the protocol has been demonstrated through gram-scale synthesis and the ease of transformation of the resulting products.

Mild Stereoselective Synthesis of Densely Substituted [3]Dendralenes via Ru-Catalyzed Intermolecular Dimerization of 1,1-Disubstituted Allenes

Described here is a mild and stereoselective protocol for the synthesis of [3]dendralenes via the intermolecular dimerization of allenes. With the proper choice of a ruthenium catalyst, a range of unactivated 1,1-disubstituted allenes, without prefunctionalization in the allylic position, reacted efficiently to provide rapid access to densely substituted [3]dendralenes. An intermolecular C-C bond and three different types of C═C double bonds (di-, tri-, and tetrasubstituted) embedded in an acyclic structure were constructed with good to high E/Z stereocontrol. This is in contrast to the known catalytic protocols that focus on allenes with prefunctionalization at the allylic position and/or monosubstituted allenes, which would proceed by a different mechanism or require less stereocontrol. The silyl-substituted dendralene products are precursors of other useful dendralene molecules. Density functional theory (DFT) studies and control experiments supported a mechanism involving oxidative cyclometalation, β-H elimination (the rate-determining step), and reductive elimination.

Photocatalytic Thiol-Yne Reactions of Alkynyl Sulfides

Thiol-yne reactions typically employ thiols and terminal alkynes as the reaction partners. The thiol-yne reaction of alkynyl sulfides and thiols is possible when employing a nonmetal photocatalyst eosin Y, green LED irradiation, under an air atmosphere. Alkynyl sulfides were transformed in good overall yields (58-90% total yields, 11 examples) favoring the cis isomer. No addition to the α-position of the alkynyl sulfide is observed, and regioselectivity is believed to be controlled through the stabilization of radical intermediates by the adjacent sulfur atom. Furthermore, control experiments with "all-carbon" internal alkynes demonstrate that alkynyl sulfides possess improved reactivity and regioselectivity profiles during thiol-yne processes.

Synthesis of Aryl Thioalkynes Enabled by Electrophilic Sulfenylation of Alkynes and the Following Elimination

An unexpected deprotonative process of thiirenium ions is presented, which provides a new synthesis of aryl thioalkynes directly from terminal alkynes via the electrophilic activation of the carbon-carbon triple bonds. The conditions are well compatible with various functional-group-substituted aryl alkynes. The direct elimination from the thiirenium ion intermediate, or its tautomer, benzyl vinyl carbocation, is supported by control experiments and labeling reaction.

Organic Base-Facilitated Thiol-Thioalkyne Reaction with Exclusive Regio- and Stereoselectivity

Here, we report the regiospecific hydrothiolation of electron-rich thioalkynes with exclusive stereoselectivity facilitated by an organic base, which could proceed exceedingly fast under ambient atmosphere and room temperature, affording β trans addition products in up to nearly quantitative yields. The dual nature of the sulfur atom in attracting and donating electrons is supposed to be pivotal in determining the regio- and stereoselectivity. This system tolerates a wide range of thiols and thioalkynes and shows great potential in polymer synthesis.

Asymmetric anti-Selective Borylalkylation of Terminal Alkynes by Nickel Catalysis

Selective transformation of alkyne triple bonds to double bonds serves as an efficient platform to construct substituted alkenes. While significant advances have been made in its spatiotemporal regulation, achieving a multicomponent enantioselective reaction that requires multifaceted selectivity issues to be overcome is still uncommon. Here, we report an unprecedented asymmetric anti-stereoselective borylcarbofunctionalization of terminal alkynes by nickel catalysis. The utilization of an inexpensive chiral diamine ligand enables the three-component cross-coupling of terminal alkynes, a diboron reagent, and prochiral alkyl electrophiles with high levels of regio-, stereo-, and enantioselectivities. This reaction provides an efficient protocol to access enantioenriched alkenyl esters bearing an α-stereogenic center, is remarkably practical, and has a broad scope and an outstanding functional group compatibility. In addition, the value of this method has been highlighted in a diversity of follow-up stereoretentive derivatizations and the stereoselective concise synthesis of complex drug molecules.

Hydrosilylation of Terminal Alkynes Catalyzed by an Air-Stable Manganese-NHC Complex

In recent years, catalysis with base metal manganese has received a significant amount of interest. Catalysis with manganese complexes having N-heterocyclic carbenes (NHCs) is relatively underdeveloped in comparison to the extensively investigated manganese catalysts possessing pincer ligands (particularly phosphine-based ligands). Herein, we describe the synthesis of two imidazolium salts decorated with picolyl arms (L₁ and L₂) as NHC precursors. Facile coordination of L₁ and L₂ with MnBr(CO)₅ in the presence of a base resulted in the formation manganese(I)-NHC complexes (1 and 2) as an air-stable solid in good isolated yield. Single-crystal X-ray analysis revealed the structure of the cationic complexes [Mn(CO)₃(NHC)][PF₆] with tridentate N,C,N binding of the NHC ligand in a facile fashion. Along with a few known manganese(I) complexes, these Mn(I)-NHC complexes 1 and 2 were tested for the hydrosilylation of terminal alkynes. Complex 1 was proved to be an effective catalyst for the hydrosilylation of terminal alkynes with good selectivity toward the less thermodynamically stable β-(Z)-vinylsilanes. This method provided good regioselectivity (anti-Markovnikov addition) and stereoselectivity (β-(Z)-product). Experimental evidence suggested that the present hydrosilylation pathway involved an organometallic mechanism with manganese(I)-silyl species as a possible reactive intermediate.

Ir-Catalyzed Regioselective Dihydroboration of Thioalkynes toward Gem-Diboryl Thioethers

While 1,1-diboryl (gem-diboryl) compounds are valuable synthetic building blocks, currently, related studies have mainly focused on those 1,1-diboryl alkanes without a hetero functional group in the α-position. gem-Diboryl compounds with an α-hetero substituent, though highly versatile, have been limitedly accessible and thus rarely utilized. Herein, we have developed the first α-dihydroboration of heteroalkynes leading to the efficient construction of gem-diboryl, hetero-, and tetra-substituted carbon centers. This straightforward, practical, mild, and atom-economic reaction is an attractive complement to the conventional multistep synthetic strategy relying on deprotonation of gem-diborylmethane by a strong base. Specifically, [Ir(cod)(OMe)]₂ was found to be uniquely effective for this process of thioalkynes, leading to excellent α-regioselectivity when delivering the two boryl groups, which is remarkable in view of the many competitive paths including monohydroboration, 1,2-dihydroboration, dehydrodiboration, triboration, tetraboration, etc. Control experiments combined with DFT calculations suggested that this process involves two sequential hydroboration events. The second hydroboration requires a higher energy barrier due to severe steric repulsion in generating the highly congested α-sulfenyl gem-diboryl carbon center, a structural motif that was almost unknown before.

Ruthenium-Catalyzed Geminal Hydroborative Cyclization of Enynes

Disclosed here is the first geminal (gem-) hydroborative cyclization of enynes. Different from known hydroborative cyclizations, this process adds hydrogen and boron to the same position, leading to a new reaction mode. With [Cp*RuCl]₄ as catalyst, a range of gem-hydroborated bicyclic products bearing a cyclopropane unit could be rapidly assembled from simple enyne substrates. Control experiments and density functional theory (DFT) calculations provided important insights into the reaction mechanism. Notably, two major competing pathways may operate with substrate-dependence. 1,6-Enynes favor initial oxidative cyclometalation to form a ruthenacyclopentene intermediate prior to engaging hydroborane, while other enynes (e.g., 1,7-enynes) that lack strong propensity toward cyclization prefer initial alkyne gem-(H,B)-addition to form an α-boryl ruthenium carbene followed by intramolecular olefin cyclopropanation. This process also represents the first ruthenium-catalyzed enyne hydroborative cyclization.

Ru-Catalyzed Hydroboration of Ynones Leads to a Nontraditional Mode of Reactivity

Although hydroboration of simple ketones and alkynes have been well-established, little is known about the unique hydroboration reactivity for ynones, a family of important building blocks. Herein we report a new reaction mode of ynones leading to structurally novel and synthetically useful but previously inaccessible products, vinyl α-hydroxylboronates, under mild ruthenium-catalyzed hydroboration conditions. This reaction features high efficiency, a broad scope, and complete chemo-, regio-, and stereoselectivity, in spite of many possible competitive pathways. Both control experiments and detailed DFT studies suggested a two-step mechanism, involving initial rate-determining conjugate addition of hydroborane to form the key boryl allenolate intermediate followed by a fast second hydroboration of the enolate motif of the allenolate. Notably, direct 1,4-addition of hydroborane to carbonyl-conjugated alkynes also represents a new mode of reactivity. Despite the overwhelming complexity of this process, which involves selectivity control in almost every step, a thorough and detailed computation on a large set of possible transition states explained the unusual reactivity and intrinsic origin of selectivity.

Diastereoselective access to substituted oxetanes via hydrosilylation-iodocyclisation of homopropargylic alcohols

The regio and stereoselective hydrosilylation of a variety of homopropargylic alcohols and their derivatives is described. The reaction is tolerant to a variety of sterically and electronically varied substrates, affording only the E-vinyl silane as a sole regioisomer. The application of the resultant vinyl silanes towards the diastereoselective synthesis of tetrasubstituted oxetanes is demonstrated.

Copper-catalyzed regio- and stereo-selective hydrosilylation of terminal allenes to access (E)-allylsilanes

Regioselectivity and stereoselectivity control in hydrosilylation of terminal allenes is challeging. Although the selective synthesis of vinylsilanes, branched allylsilanes or linear (Z)-allylsilanes have been achieved, transition-metal catalyzed hydrosilylation of terminal allenes to access (E)-allylsilane is difficult. Herein, we report a copper-catalyzed selective hydrosilylation reaction of terminal allenes to access (E)-allylsilanes under mild reaction conditions. The reaction shows broad substrate scope, representing an efficient method to prepare trisubstituted (E)-allylsilanes through hydrosilylation reaction of allenes and can also be applied in the synthesis of disubstituted (E)-allylsilanes. The mechanism study reveals that the E-selectivity is kinetically controlled by the catalyst but not by the thermodynamically isomerization of the (Z)-isomer.

Regio- and stereoselective transition-metal catalysed hydrosilylation of terminal allenes to access (E)-allylsilanes are challenging organic transformations. Herein, the authors synthesize (E)-allylsilanes via copper-catalyzed hydrosilylation of terminal allenes.

Recyclable Gold Catalyst for the Stereoselective Thioallylation of Alkynes

The heterogeneous gold(I)-catalyzed stereoselective thioallylation of electron-deficient alkynes with allyl sulfides has been achieved by using an MCM-41-immobilized sterically demanding NHC-gold(I) complex [MCM-41-IPrAuNTf₂] as the catalyst under mild conditions, delivering a wide variety of stereodefined tri- and tetrasubstituted functionalized vinyl sulfides in good to excellent yields. The new heterogeneous MCM-41-IPrAuNTf₂ catalyst exhibits an activity comparable to a homogeneous IPrAuNTf₂ complex and can be recovered via a simple filtration process and reused for at least seven consecutive cycles without any apparent loss of its catalytic activity and selectivity.

Transition-Metal-Catalyzed Stereo- and Regioselective Hydrosilylation of Unsymmetrical Alkynes

Alkyne hydrosilylation is one of the most efficient methods for the synthesis of alkenyl silicon derivatives and has been a hot topic of research for decades. This short review summarizes the progress in transition-metal-catalyzed stereo- and regioselective hydrosilylation of unsymmetrical alkynes. Topics are discussed based on different types of alkynes and the selectivities.

1 Introduction

2 Terminal Alkyne Hydrosilylation

2.1 β-E Selectivity

2.2 β-Z Selectivity

2.3 α-selectivity

3 Internal Alkyne Hydrosilylation

3.1 Aryl–Alkyl Acetylenes

3.2 Alkyl–Alkyl Acetylenes

3.3 Internal Alkynes with Polarized Substituents

4 Summary and Outlook

Markovnikov Hydrosilylation of Alkynes with Tertiary Silanes Catalyzed by Dinuclear Cobalt Carbonyl Complexes with NHC Ligation

Metal-catalyzed hydrosilylation of alkynes is an ideal atom-economic method to prepare vinylsilanes that are useful reagents in the organic synthesis and silicone industry. Although great success has been made in the preparation of β-vinylsilanes by metal-catalyzed hydrosilylation reactions of alkynes, reported metal-catalyzed reactions for the synthesis of α-vinylsilanes suffer from narrow substrate scope and/or poor selectivity. Herein, we present selective Markovnikov hydrosilylation reactions of terminal alkynes with tertiary silanes using a dicobalt carbonyl N-heterocyclic carbene (NHC) complex [(IPr)₂Co₂(CO)₆] (IPr = 1,3-di(2,6-diisopropylphenyl)imidazol-2-ylidene) as catalyst. This cobalt catalyst effects the hydrosilylation of both alkyl- and aryl-substituted terminal alkynes with a variety of tertiary silanes with good functional group compatibility, furnishing α-vinylsilanes with high yields and high α/β selectivity. Mechanistic study revealed that the stoichiometric reactions of [(IPr)₂Co₂(CO)₆] with PhC≡CH and HSiEt₃ can furnish the dinuclear cobalt alkyne and mononuclear cobalt silyl complexes [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃], [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₂(IPr)], and [(IPr)Co(CO)₃(SiEt₃)], respectively. Both dicobalt bridging alkyne complexes can react with HSiEt₃ to yield α-triethylsilyl styrene and effect the catalytic Markovnikov hydrosilylation reaction. However, the mono(NHC) dicobalt complex [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃] exhibits higher catalytic activity over the di(NHC)-dicobalt complexes. The cobalt silyl complex [(IPr)Co(CO)₃(SiEt₃)] is ineffective in catalyzing the hydrosilylation reaction. Deuterium labeling experiments with PhC≡CD and DSiEt₃ indicates the syn-addition nature of the hydrosilylation reaction. The absence of deuterium scrambling in the hydrosilylation products formed from the catalytic reaction of PhC≡CH with a mixture of DSiEt₃ and HSi(OEt)₃ hints that mononuclear cobalt species are less likely the in-cycle species. These observations, in addition to the evident of nonsymmetric Co₂C₂-butterfly core in the structure of [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃], point out that mono(IPr)-dicobalt species are the genuine catalysts for the cobalt-catalyzed hydrosilylation reaction and that the high α selectivity of the catalytic system originates from the joint play of the dicobalt carbonyl species to coordinate alkynes in the Co(μ-η²:η²-HCCR')Co mode and the steric demanding nature of IPr ligand.

Iridium-catalyzed regioselective hydrosilylation of internal alkynes facilitated by directing and steric effects

Here we reported the iridium-catalyzed hydrosilylation of internal alkynes under simple and mild conditions. The intrinsic functional groups of alkyne substrates were disclosed to be crucial in facilitating both the hydrosilylation process and related regioselectivity owing to their coordination capability towards the iridium catalyst. Utilization of the steric trimethylsilyl-protected trihydroxysilane proved to be another critical factor in ensuring the efficient proceeding of this process.

Computational Insight into Cu-Catalyzed Csp-S Coupling to Form a Macrocyclic Alkynyl Sulfide

Copper-catalyzed C_sp-S cross-coupling is known to form rare macrocyclic alkynyl sulfides. Computational studies now suggest a mechanism for the reaction pathway. Upon formation of Cu-S species, subsequent α-addition/elimination at the ethynylic carbon affords the desired macrocycle.

Synthesis and Diversification of Macrocyclic Alkynediyl Sulfide Peptides

The synthesis of rare macrocyclic alkynediyl sulfides by a Cu-catalyzed C_sp -S cross-coupling is presented. The catalytic protocol (Cu(MeCN)₄ PF₆ /dtbbpy) promotes macrocyclization of peptides, dipeptides and tripeptides at ambient temperature (14 examples, 23→73 % yields) via thiols and bromoalkynes, and is chemoselective with regards to terminal alkynes. Importantly, the underexplored alkynediyl sulfide functionality incorporates a rigidifying structural element and opens new opportunities for diversification of macrocyclic frameworks through S oxidation, halide addition and azide-alkyne cycloaddition chemistries to integrate sulfones, halides or valuable fluorophores (7 examples, 37→92 % yields).

Understanding the unique reactivity patterns of nickel/JoSPOphos manifold in the nickel-catalyzed enantioselective C-H cyclization of imidazoles

The 3d transition metal-catalyzed enantioselective C–H functionalization provides a sustainable strategy for the construction of chiral molecules. A better understanding of the catalytic nature of the reactions and the factors controlling the enantioselectivity is important for rational design of more efficient systems. Herein, the mechanisms of Ni-catalyzed enantioselective C–H cyclization of imidazoles are investigated by density functional theory (DFT) calculations. Both the π-allyl nickel(ii)-promoted σ-complex-assisted metathesis (σ-CAM) and the nickel(0)-catalyzed oxidative addition (OA) mechanisms are disfavored. In addition to the typically proposed ligand-to-ligand hydrogen transfer (LLHT) mechanism, the reaction can also proceed via an unconventional σ-CAM mechanism that involves hydrogen transfer from the JoSPOphos ligand to the alkene through P–H oxidative addition/migratory insertion, C(sp²)–H activation via σ-CAM, and C–C reductive elimination. Importantly, computational results based on this new mechanism can indeed reproduce the experimentally observed enantioselectivities. Further, the catalytic activity of the π-allyl nickel(ii) complex can be rationalized by the regeneration of the active nickel(0) catalyst via a stepwise hydrogen transfer, which was confirmed by experimental studies. The calculations reveal several significant roles of the secondary phosphine oxide (SPO) unit in JoSPOphos during the reaction. The improved mechanistic understanding will enable design of novel enantioselective C–H transformations.

Several unique reactivity patterns of the Ni/JoSPOphos manifold, including facile hydrogen transfer via the two-step oxidative addition/migratory insertion and C(sp²)–H activation via an unconventional σ-CAM mechanism, were disclosed in this work.

General Cu-Catalyzed Csp-S Coupling

Copper-catalyzed cross-coupling of thiols and bromoalkynes affords a mild, rapid, and selective C_sp-S coupling with broad scope, enabling the use of aryl-, alkyl-, and silyl-substituted alkynyl coupling partners (38 total examples, 50-99% yields). Importantly, the method enables the preparation of difficult-to-access bis-heteroatom-functionalized (S,S-, S,P-, and S,N-) alkynes.

Iron-Catalyzed Asymmetric Hydrosilylation of Vinylcyclopropanes via Stereospecific C-C Bond Cleavage

An iron-catalyzed highly anti-Markovnikov selective, enantioselective hydrosilylation of vinylcyclopropanes with PhSiH₃ was reported for the preparation of valuable chiral allylic silanes via stereospecific C-C bond cleavage. Simultaneously, difficultly prepared chiral VCPs could be also obtained with moderate to excellent enantioselectivity via this kinetic resolution pathway. The chiral Z-allylic silanes could be converted to various chiral allylic derivatives. A possible mechanism via an iron-silyl species was proposed based on experimental and computational studies.

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Iron-catalyzed 1,5-hydrosilylation of VCPs via C-C bond cleavage was first established

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Chiral allyl silanes and chiral VCPs were obtained with high enantioselectivity

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Various chiral allylic derivatives were delivered from chiral Z-allylic silanes

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A possible mechanism via an iron-silyl species was proposed

One simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers

Here, we describe one simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers. This facile strategy shows high efficiency towards a variety of substrates, including derivatives from bioactive molecules. The substituent at the α position of the olefins is supposed to be critical in retarding the alkene hydrosilylation process and leading the reaction to go through the isomerization pathway.

Synthesis of Stereodefined Trisubstituted Alkenyl Silanes Enabled by Borane Catalysis and Nickel Catalysis

Regioselective and stereoselective synthesis of trisubstituted alkenyl silanes via hydrosilylation is challenging. Herein, we report the first β-anti-selective addition of silanes to thioalkynes with B(C₆F₅)₃ as the catalyst. The reaction shows broad substrate scope. The products were proven to be useful intermediates to other trisubstituted alkenyl silanes by Ni-catalyzed stereoretentive cross-coupling reactions of the C-S bond. A mechanism study suggests that nucleophilic attack of thioalkyne to an activated silylium intermediate might be the rate-determining step.

Synthesis of 2H-Chromenes via Unexpected [4 + 2] Annulation of Alkynyl Thioethers with o-Hydroxybenzyl Alcohols

A novel Brønsted acid-catalyzed reaction of alkynyl thioethers with o-hydroxybenzyl alcohols via an unexpected formal [4 + 2] annulation has been developed. This metal-free protocol leads to the facile and practical synthesis of valuable polysubstituted 2H-chromenes in mostly good to excellent yields under mild reaction conditions and features a wide substrate scope and excellent functional group tolerance.

Regiocontrol in the cobalt-catalyzed hydrosilylation of alkynes

A highly versatile cobalt-catalyzed hydrosilylations of alkynes is reported. Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Hydrofunctionalizations of unsaturated hydrocarbons are key strategies for the synthesis of functionalized building blocks. Here, we report highly versatile cobalt-catalyzed hydrosilylations of alkynes that operate with minute amounts of the inexpensive, bench-stable pre-catalyst Co(OAc)₂·4H₂O under mild conditions (0.1–1 mol%, THF, r.t., 1 h). Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Highly β( Z)-Selective Hydrosilylation of Terminal Alkynes Catalyzed by Thiolate-Bridged Dirhodium Complexes

A series of novel monothiolate-bridged dirhodium complexes, [Cp*Rh(μ-SR)(μ-Cl)₂RhCp*][BF₄] {Cp* = η⁵-C₅Me₅, R = tertiary butyl ( ^tBu), 1a; R = ferrocenyl (Fc), 1b; R = adamantyl (Ad), 1c} were designed and successfully synthesized, which can smoothly facilitate highly regioselective and stereoselective hydrosilylation of terminal alkynes to afford β( Z) vinylsilanes with good functional group compatibility. Furthermore, the hydride bridged dirhodium complex [Cp*Rh(μ-S ^tBu)(μ-Cl)(μ-H)RhCp*][BF₄] (5) as a potential intermediate was obtained by the reaction of 1a with excess HSiEt₃.

Zinc-catalyzed reaction of isoxazoles with thioynol ethers involving an unprecedented 1,2-sulfur migration

A novel zinc-catalyzed reaction of isoxazoles with thioynol ethers involving an unprecedented 1,2-sulfur migration has been developed, which represents the first example of a non-noble metal-catalyzed reaction between isoxazoles and alkynes. This method allows the facile and atom-economical synthesis of a range of valuable β-keto enamides. Moreover, the computational study provides further evidence for the feasibility of the proposed reaction mechanism.

Silylation reactions on nanoporous gold via homolytic Si-H activation of silanes

We report compelling evidences that dihydrosilanes are activated in a homolytic fashion on the surface of nanoporous gold (NPG), which produces hydrogen radical and silicon moieties covalently linked to the surface of the NPG. This new reactivity has led to the development of novel silylation reactions on gold.

Si–H bond activation is an important process implicated in many useful synthetic applications including silylation and transfer hydrogenation reactions. Herein we discovered homolytic activation of Si–H bonds on the surface of nanoporous gold (NPG), forming hydrogen radicals and [Au]–[Si] intermediates. By virtue of this new reactivity, we achieved highly selective mono and sequential alcoholysis of dihydrosilane. In addition, the amphiphilic nature of the [Au]–[Si] intermediate allows for a new bis-silylation reaction of cyclic ethers. The present work showcased that the surface reactivity of nanocatalysts may provide exciting opportunity for new reaction discovery.