Copper(II)-catalyzed silylation of activated alkynes in water: diastereodivergent access to E- or Z-β-silyl-α,β-unsaturated carbonyl and carboxyl compounds

Anti-Selective Carbosilylation: Nickel-Catalyzed Multicomponent Reaction of Solid Me3SiZnI

The stereodefined and highly substituted vinylsilanes are essential building blocks for constructing complex organic molecules. Transition metal-mediated silylmetalation of alkynes was developed to overcome the limitations of conventional hydrosilylations; however, a very limited study was carried out to utilize transient vinylmetal species in cross-coupling reactions. Moreover, they produce syn-adduct, and the anti-selective cross-coupling is still unknown and highly desired. Silylzinc reagents are highly functional group tolerant, however, their synthesis from pyrophoric silyllithium and dissolved lithium salts hampers cross-coupling reactions. Our novel solid silylzinc reagents circumvent these constraints are employed in the anti-selective synthesis of vinylsilanes via a multi-component reaction involving Me3SiZnI, terminal alkynes, and activated alkyl halides. An intensive computational and experimental investigation of the mechanism reveals an equilibrium between the intermediate syn- and anti-adducts; the greater barrier at the single electron reduction of alkyl halides and the thermodynamic stability of the Ni(III) adduct determine the anti-selectivity.

Cu-Catalyzed Synthesis of 2-Silyl-1,3-butadienes from Allenols and Applications to One-Pot Synthesis of Tetrasubstituted Arylsilanes

A copper-catalyzed chemo- and stereoselective method for the synthesis of (E)-2-silyl-1,3-butadienes from a broad range of allenols using mild Si-B reagents is reported in this study. Our protocol required a short reaction time at ambient temperature to produce the desired dienes in high yields. Synthetic applications are highlighted by the one-pot synthesis of tetrasubstituted arylsilanes from allenols as well as the further functionalization of C-Si bonds.

Cobalt-Promoted Electroreductive Cross-Coupling of Prop-2-yn-1-yl Acetates with Chloro(vinyl)silanes

An electroreductive cross-coupling of prop-2-yn-1-yl acetates with chloro(vinyl)silanes for producing tetrasubstituted silylallenes is developed. The method enables the formation of a new C─Si bond through the cathodic reduction formation of the silyl radical, radical addition across the C≡C bond, the alkenyl anion intermediate formation, and deacetoxylation and represents a mild, practical route to the synthesis of silylallenes. Mechanistic studies reveal that CoCl2 acts as the mediator to promote the formation of the alkenyl anion intermediate via electron transfer.

Copper-Catalyzed Enantioselective Desymmetric Protosilylation of Prochiral Diynes: Access to Optically Functionalized Tertiary Alcohols

In this protocol, a copper-catalyzed desymmetric protosilylation of prochiral diynes was developed. The corresponding products were obtained in moderate to high yields and enantiomeric ratios. This approach provides a simple method for synthesizing functionalized chiral tertiary alcohols in the presence of a chiral pyridine-bisimidazoline (Pybim) ligand.

Palladium/Copper-Cocatalyzed Arylsilylation of Internal Alkynes with Acyl Fluorides and Silylboranes: Synthesis of Tetrasubstituted Alkenylsilanes by Three-Component Coupling Reaction

In this Letter, the palladium/copper-cocatalyzed arylsilylation of internal alkynes with acyl fluorides and silylboranes is described. This is the first example in which acyl fluorides have been utilized for the three-component coupling reaction via decarbonylation, yielding a variety of tetrasubstituted alkenylsilanes in moderate to good yields.

Recent advances in Cu-catalyzed transformations of internal alkynes to alkenes and heterocycles

Numerous metal-catalyzed reactions involving internal alkynes and aimed towards synthetically and pharmacologically important alkenes and heterocycles have appeared in the literature. Among these, Cu-catalyzed reactions have a special place, which has prompted the investigation and development of carbon-carbon and carbon-heteroatom bond-forming reactions. These reactions possess wide scope, and during the paths of these reactions, either stable or in situ intermediates are formed via the addition of Cu as a core catalyst or synergistic catalyst. In this review, we aim to report different contributions relating to Cu-catalyzed reactions of internal alkynes for the synthesis of different valuable alkenes and heterocycles which have appeared in the literature in the last decade. We anticipate that this appraisal will deliver basic insights for the further advancement of Cu-catalyzed reactions in organic chemistry.

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.

Copper-catalyzed regioselective trans-silaboration of internal arylalkynes with stereochemical switch to cis-addition mode

Copper-catalyzed silafunctionalization of alkynes using a silylboronic ester as a silicon source has recently progressed rapidly. Generally, the reaction affords a product with cis-stereoselectivity. We herein describe trans-selective 1,2-addition of silylboronic esters to internal arylalkynes, which was promoted efficiently by the CuOt-Bu/RCy2P/NaOt-Bu catalysts. Moreover, we report a stereochemical switch to cis-addition in the reactions of Me2(i-PrO)Si-B(pin) in hydrocarbon solvents including cyclohexane.

Activation of the Si–B interelement bond related to catalysis

Covering the past seven years, this review comprehensively summarises the latest progress in the preparation and application of Si–B reagents, including the discussion of relevant reaction mechanisms.

Alkynyl Linkers as a Design Tool to Gain Control over the Self-Assembly of Meso-Substituted Porphyrins on HOPG

Self-assembled monolayers (SAMs) fall generally into two broad categories: those that are covalently bound either to the surface or to each other and those that rely on weaker forces such as hydrogen bonding or van der Waals forces. The engineering of the structure of SAMs formed from weaker forces is an exciting and complex field that often utilizes long alkane substituents bound to core moieties. The core provides the unique optical, electronic, or catalytic property desired, while the interdigitation of the alkane chains provides the means for creating well-regulated patterns of cores on the substrate. This design technique sometimes fails because some of the alkane substituents remain extended into solution rather than become interdigitated on the substrate. One contributor to this is steric hindrance between elements of the core and of the alkane chain. It is shown that the use of an alkyne linker between the core and the alkane chain can, in the case of meso-substituted porphyrins, significantly reduce this steric barrier and allow more stable and predictable surface structures to form. In particular, 5,15-bis(1-octynyl)porphyrin and 5,15-bis(1-tetradecynyl)porphyrin are shown to form significantly more stable SAMs than their alkane-linked counterparts. Scanning tunneling microscopy is used to provide detailed surface structures. Temperature and solution concentration dependence of the surface coverage is also reported. Density functional theory (DFT) is used to determine the energetic effects associated with alkane substitution at both the meso and β positions and the beneficial energetic effects of the alkyne linker.

Copper-catalyzed regiodivergent 1,4- and 1,6-conjugate silyl addition to diendioates: access to functionalized allylsilanes

A copper-catalyzed regioselective 1,4- and 1,6-conjugate addition of a silyl reagent to diendioates was established. Various 1,4- and 1,6-protosilylation products were obtained in good yields and with high regioselectivity via tuning the ligands used in the reactions. This protocol has provided a simple and efficient method for the synthesis of multisubstituted functionalized allylsilanes.

Divergent Protosilylation and Protoborylation of Polar Enynes

Copper-catalyzed divergent conjugate protosilylation and protoborylation of polar enynes were developed. The corresponding β-boryldienoates and β-silyldienotes were obtained in moderate to good yields and with good stereoselectivity. In this protocol, novel cascade double protoborylation/protodeboronation processes of polar enynoates enabled access of the useful trisubstituted vinylboronates in up to 80% yield and with up to 98:2 Z/ E ratio. Moreover, divergent transformations of the products thus obtained were also investigated.

An aqueous medium-controlled stereospecific oxidative iodination of alkynes: efficient access to (E)-diiodoalkene derivatives

A new and versatile approach for the stereospecific iodination of alkynes has been developed in aqueous media. Scale-up reactions (up to 5 g) established the proficiency of this protocol and highlight the feasibility of large scale reactions.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Mechanistic study on ligand-controlled copper-catalyzed regiodivergent silacarboxylation of allenes with carbon dioxide and silylborane

The origin of ligand-controlled copper-catalyzed regiodivergent silacarboxylation was rationalized.

A Ligand-Free Pt3 Cluster Catalyzes the Markovnikov Hydrosilylation of Alkynes with up to 106 Turnover Frequencies

The Pt-catalyzed hydrosilylation of alkynes is the procedure of choice to obtain vinylsilanes, and is claimed to be the most relevant application of Pt in organic synthesis. More than half a century after its discovery, only β-vinylsilanes (anti-Markovnikov addition) are obtained with simple Pt catalysts, whereas α-vinylsilanes (Markovnikov addition) remain elusive compounds. Here the catalysis of the Markovnikov hydrosilylation of terminal alkynes by Pt₃ clusters, in parts-per-million amounts, to give a wide variety of α-vinylsilanes in reasonable isolated yields and with turnover frequencies that can reach up to one million per hour is reported. Moreover, these α-vinylsilanes are reactive in well-stablished C-C bond-forming cascade reactions, in which the corresponding β-isomers are unreactive. Besides its efficiency and synthetic usefulness, this catalytic system is an excellent example of how the atom-by-atom aggregation of a catalytic metal leads to a different selectivity for a given reaction.

Intermolecular Three-Component Arylsilylation of Alkynes under Palladium/Copper Cooperative Catalysis

An intermolecular three-component arylsilylation of alkynes has been developed under mild palladium/copper cooperative catalysis. The reaction proceeds through syn-addition of an aryl group and a silyl group across the carbon-carbon triple bond of an alkyne. This represents the first transition-metal-catalyzed fully intermolecular arylsilylation of alkynes, and transformations of the resulting products have also been demonstrated.

Substrate-controlled switchable asymmetric annulations to access polyheterocyclic skeletons

Substrate-controlled switchable asymmetric annulations of Morita–Baylis–Hillman carbonates from isatins and α-cyano-α,β-unsaturated ketones catalysed by cinchona-derived tertiary amines, giving tetrahydrofuro[2′,3′:4,5]pyrano[2,3-b]indoles or spirooxindoles incorporating a cyclopentene motif, were disclosed.

Organocatalytic silyl transfer from silylborane to nitroalkenes for the synthesis of β-silyl nitroalkanes and β-silyl amines

We discovered organocatalytic silyl transfer from silylborane to nitroalkenes in a toluene/water biphasic solvent. A variety of functionalized β-silyl nitroalkanes were obtained in moderate to excellent yields, which provides access to biologically interesting β-silyl amines.

Palladium-catalyzed silylation reaction between benzylic halides and silylboronate

An efficient Pd-catalyzed silylation reaction of benzylic halides with silylboronate is reported. In this reaction, primary and secondary benzylic halides could react well with silylboronates to afford benzylic silanes. This reaction accommodates a broad substrate scope and proceeds smoothly under very mild reaction conditions. The corresponding products could be obtained in moderate to high yields and with stereospecificity.

Copper(ii)-catalyzed highly regio- and stereo-selective hydrosilylation of unactivated internal alkynes with silylborate in water

The hydrosilylation of internal alkynes with Me₂PhSiBpin catalyzed by Cu(OTf)₂ in water provided multisubstituted vinylsilanes in high regio- and stereoselectivities.