The Hiyama Cross-Coupling Reaction: New Discoveries

Palladium-Catalyzed Ring-Opening Defluorinative Hiyama Cross-Coupling of gem-Difluorocyclopropanes with Arylsilanes

We report an efficient palladium-catalyzed ring-opening defluorinative Hiyama cross-coupling of gem-difluorocyclopropanes with structurally diverse (hetero)arylsilanes through C-C bond activation and C-F bond cleavage. This regioselective ring-opening defluorinative Hiyama cross-coupling features a broad substrate scope with excellent functional group compatibility, affording a diverse variety of linear 2-fluoroallylic scaffolds in good yields with high Z-selectivity.

Palladium-Catalyzed Hiyama Cross-Coupling of Heterocyclic Phosphonium Salts with Arylsilanes

We report herein the palladium-catalyzed Hiyama cross-coupling of heterocyclic phosphonium salts with diverse (hetero)arylsilanes through C-P bond cleavage, providing an alternative approach for the highly regioselective functionalization of pyridines and relevant nitrogen-containing heterocycles. This silicon-based protocol is amenable to gram-scale synthesis and also applicable to the late-stage functionalization of pharmaceutically relevant complex molecules.

Nickel-Catalyzed Stereospecific Alkylation of Vinylsiloxanes Using Pyridinium Salts

A methodology for radical cross-coupling with vinylsiloxanes and pyridinium salts under nickel catalysis is described. Easily implemented from inexpensive and abundant primary amines and terminal alkynes, this Hiyama coupling provides efficient access to (E), (Z), and (1,1')-alkenes with selectivity control. Operating under mild conditions, this robust strategy applies to a broad range of functional groups with diverse double bond stereochemistries. This versatile reaction is scalable and straightforward, accommodating both secondary and primary alkyl groups.

Palladium-Catalyzed Hiyama-Type Coupling of Thianthrenium and Phenoxathiinium Salts

Here, we demonstrate palladium-catalyzed Hiyama-type cross-coupling reactions of aryl thianthrenium or phenoxathiinium salts. By employing stable and inexpensive organosilanes, the arylation, alkenylation, and alkynylation were realized in high efficiency using commercially available Pd(tBu3P)2 as the catalyst, thus providing a reliable method for preparation of biaryls, styrenes, and aryl acetylenes with a broad functional group tolerance under mild conditions. Given the accessibility of aryl thianthrenium or phenoxathiinium salts from simple arenes in a remarkable regioselective fashion, this protocol also provides an attractive approach for the late-stage modification of complex bioactive scaffolds.

Construction of Si-Stereogenic Silanols by Palladium-Catalyzed Enantioselective C-H Alkenylation

The construction of silicon-stereogenic silanols via Pd-catalyzed intermolecular C-H alkenylation with the assistance of a commercially available L-pyroglutamic acid has been realized for the first time. Employing oxime ether as the directing group, silicon-stereogenic silanol derivatives could be readily prepared with excellent enantioselectivities, featuring a broad substrate scope and good functional group tolerance. Moreover, parallel kinetic resolution with unsymmetric substrates further highlighted the generality of this protocol. Mechanistic studies indicate that L-pyroglutamic acid could stabilize the Pd catalyst and provide excellent chiral induction. Preliminary computational studies unveil the origin of the enantioselectivity in the C-H bond activation step.

Stereoselective Palladium-Catalyzed Hiyama Cross-Coupling Reaction of Tetrasubstituted gem-Difluoroalkenes

We herein describe a diastereoselective Pd(0)-catalyzed Hiyama cross-coupling reaction of gem-difluoroalkenes. The use of organosilicon reagents in this reaction is advantageous over other organometallic reagents by allowing the introduction of a wide range of functional groups, including challenging alkyl groups. Also conveniently, the additive TBAF was not required for (hetero)aryl-substituted difluoroalkenes.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

This review provides recent developments in the current status and latest synthetic methodologies of biphenyl derivatives. Furthermore, this review investigates detailed discussions of several metalated chemical reactions related to biphenyl scaffolds such as Wurtz-Fittig, Ullmann, Bennett-Turner, Negishi, Kumada, Stille, Suzuki-Miyaura, Friedel-Crafts, cyanation, amination, and various electrophilic substitution reactions supported by their mechanistic pathways. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. Furthermore, atropisomerism as a type of axial chirality in biphenyl molecules is discussed. Additionally, this review covers a wide range of biological and medicinal applications of the synthesized compounds involving patented approaches in the last decade corresponding to investigating the crucial role of the biphenyl structures in APIs.

Recent advances in carbosilylation of alkenes and alkynes

Alkene and alkyne difunctionalization is a flexible process that allows the construction of two functional groups simultaneously in one step. On the other hand, carbosilylation, an ingenious difunctionalization pathway to concurrently incorporate both a silyl group and an organic functional group (alkyl, (hetero)aryl, alkenyl, alkynyl and allenyl) across a carbon-carbon multiple-bond system, is achieving immense interest in recent days. This review article provides a decade's update on the discoveries and developments in the synthesis of carbosilylated products from two very important carbon-carbon unsaturated substrates, alkenes and alkynes.

Palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines by intramolecular Hiyama coupling

A palladium-catalyzed synthesis of 4-sila-4H-benzo[d][1,3]oxazines, silicon-switched analogs of biologically relevant 4H-benzo[d][1,3]oxazines, was developed by the intramolecular Hiyama coupling of 3-amido-2-(arylsilyl)aryl triflates.

Sila-spirocyclization involving unstrained C(sp3)-Si bond cleavage

C - Si Bond cleavage is one of the key elemental steps for a wide variety of silicon-based transformations. However, the cleavage of unstrained Si-C(sp3) bonds catalyzed by transition metal are still in their infancy. They generally involve the insertion of a M - C(sp2) species into the C - Si bond and consequent intramolecular C(sp2)‒Si coupling to exclusively produce siloles. Here we report the Pd-catalyzed sila-spirocyclization, in which the Si-C(sp3) bond is activated by the insertion of a M - C(sp3) species and followed by the formation of a new C(sp3)‒Si bond, allowing the construction of diverse spirosilacycles. This reactivity mode, which is strongly supported by DFT calculations may open an avenue for the Si-C(sp3) bond cleavage and silacycle synthesis.

Transition Metal Catalyzed Hiyama Cross-Coupling: Recent Methodology Developments and Synthetic Applications

Hiyama cross-coupling is a versatile reaction in synthetic organic chemistry for the construction of carbon-carbon bonds. It involves the coupling of organosilicons with organic halides using transition metal catalysts in good yields and high enantioselectivities. In recent years, hectic progress has been made by researchers toward the synthesis of diversified natural products and pharmaceutical drugs using the Hiyama coupling reaction. This review emphasizes the recent synthetic developments and applications of Hiyama cross-coupling.

Meta-Selective C-H Functionalization of Arylsilanes Using a Silicon Tethered Directing Group

We describe meta-selective C-H functionalization of arylsilanes using a Si-tethered directing group. The current method enables a selective alkenylation of arenes bearing a variety of functional groups, and several electron-deficient olefins are also applicable as coupling partners. Further functional group transformations of the silicon-tethered directing group provide multisubstituted arenes efficiently.

Inorganometallics (Transition Metal-Metalloid Complexes) and Catalysis

While the formation and breaking of transition metal (TM)-carbon bonds plays a pivotal role in the catalysis of organic compounds, the reactivity of inorganometallic species, that is, those involving the transition metal (TM)-metalloid (E) bond, is of key importance in most conversions of metalloid derivatives catalyzed by TM complexes. This Review presents the background of inorganometallic catalysis and its development over the last 15 years. The results of mechanistic studies presented in the Review are related to the occurrence of TM-E and TM-H compounds as reactive intermediates in the catalytic transformations of selected metalloids (E = B, Si, Ge, Sn, As, Sb, or Te). The Review illustrates the significance of inorganometallics in catalysis of the following processes: addition of metalloid-hydrogen and metalloid-metalloid bonds to unsaturated compounds; activation and functionalization of C-H bonds and C-X bonds with hydrometalloids and bismetalloids; activation and functionalization of C-H bonds with vinylmetalloids, metalloid halides, and sulfonates; and dehydrocoupling of hydrometalloids. This first Review on inorganometallic catalysis sums up the developments in the catalytic methods for the synthesis of organometalloid compounds and their applications in advanced organic synthesis as a part of tandem reactions.

Silacyclization through palladium-catalyzed intermolecular silicon-based C(sp2)-C(sp3) cross-coupling

Silicon-based cross-coupling has been recognized as one of the most reliable alternatives for constructing carbon–carbon bonds. However, the employment of such reaction as an efficient ring expansion strategy for silacycle synthesis is comparatively little known. Herein, we develop the first intermolecular silacyclization strategy involving Pd-catalyzed silicon-based C(sp²)–C(sp³) cross-coupling. This method allows the modular assembly of a vast array of structurally novel and interesting sila-benzo[b]oxepines with good functional group tolerance. The key to success for this reaction is that silicon atoms have a stronger affinity for oxygen nucleophiles than carbon nucleophiles, and silacyclobutanes (SCBs) have inherent ring-strain-release Lewis acidity.

Herein, we develop the first silacyclization between 2-halophenols and SCBs, which allows the modular assembly of sila-benzo[b]oxepines with good functional group tolerance and can be applied for the late-stage modification of biologically active molecules.

Versatile Access to Tetrasubstituted 2-Amidoacroleins through Formal Silylformylation of Ynamides

In this paper we are reporting the first regio- and stereoselective silylformylation of ynamides. This reaction is tolerant to a wide range of functional groups around the ynamides. The substitution of CO by an isocyanide makes this reaction safer and more practical than standard silylformylation reactions. It overall represents a versatile and rapid access to various tetrasubstituted 3-silyl-2-amidoacrolein derivatives. The synthetic potential of these new building blocks has been evaluated by performing several postfunctionalization.

Facile Approach to C-Glucosides by Using a Protecting-Group-Free Hiyama Cross-Coupling Reaction: High-Yielding Dapagliflozin Synthesis

Access to unprotected (hetero)aryl pseudo-C-glucosides via a mild Pd-catalysed Hiyama cross-coupling reaction of protecting-group-free 1-diisopropylsilyl-d-glucal with various (hetero)aryl halides has been developed. In addition, selected unprotected pseudo-C-glucosides were stereoselectively converted into the corresponding α- and β-C-glucosides, as well as 2-deoxy-β-C-glucosides. This methodology was applied to the efficient and high-yielding synthesis of dapagliflozin, a medicament used to treat type 2 diabetes mellitus. Finally, the versatility of our methodology was proved by the synthesis of other analogues of dapagliflozin.

A nickel-catalyzed silylation reaction of alkyl aryl sulfoxides with silylzinc reagents

Ni(PEt3)Cl2-catalyzed silylation of alkyl aryl sulfoxides with silylzinc reagents was carried out. This protocol allows alkyl aryl sulfoxides to convert to arylsilicon compounds under mild reaction conditions, tolerates a range of functional groups and is suitable for a wide scope of substrates.

A versatile iodo(III)etherification of terminal ethynylsilanes using BF3-OiPr2 and alkyl benzyl ethers

A series of (E)-α-silyl-β-alkoxyvinyl-λ3-iodanes was synthesized from iodosylbenzene, BF3-ether complexes, and terminal ethynylsilanes. The combined use of BF3-OiPr2 and benzyl ethers of primary alcohols (ROBn) allows the chemoselective transfer of primary alkoxy groups (RO) onto the β-position of the terminal ethynylsilanes.

Chemodivergent reactions

An important strategy for the efficient generation of diversity in molecular structures is the utilization of common starting materials in chemodivergent transformations. The most studied solutions for switching the chemoselectivity rely on the catalyst, ligand, additive, solvent, temperature, time, pressure, pH and even small modifications in the substrate. In this review article several processes have been selected such as inter- and intramolecular cyclizations, including carba-, oxa-, thia- and oxazacyclizations promoted mainly by Brønsted or Lewis acids, transition metals and organocatalysts, as well as radical reactions. Catalyst-controlled intra- and intermolecular cyclizations are mainly described to give five- and six-membered rings. Cycloaddition reactions involving (2+2), (3+2), (3+3), (4+1), (4+2), (5+2), (6+2) and (7+2) processes are useful reactions for the synthesis of cyclic systems using organocatalysts, metal catalysts and Lewis acid-controlled processes. Addition reactions mainly of carba- and heteronucleophiles to unsaturated conjugated substrates can give different adducts via metal catalyst-, Lewis acid- and solvent-dependent processes. Carbonylation reactions of amines and phenols are carried out via ligand-controlled transition metal-catalyzed multicomponent processes. Ring-opening reactions starting mainly from cyclopropanols, cyclopropenols and epoxides or aziridines are applied to the synthesis of acyclic versus cyclic products under catalyst-control mainly by Lewis acids. Chemodivergent reduction reactions are performed using dissolving metals, sodium borohydride or hydrogen transfer conditions under solvent control. Oxidation reactions include molecular oxygen under solvent control or using different dioxiranes, as well as chemodivergent palladium catalyzed cross-coupling reactions using boronic acids are applied to aromatic and allenic compounds. Other chemodivergent reactions such as alkylations and allylations under transition metal catalysis, dimerization of acetylenes, bromination of benzylic substrates, and A³-couplings are performed via catalyst- or reaction condition-dependent processes.

Divergent Synthesis of Vinyl-, Benzyl-, and Borylsilanes: Aryl to Alkyl 1,5-Palladium Migration/Coupling Sequences

Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through-space metal/hydrogen shifts allow functionalization of C-H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5-palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl-, benzyl-, and borylsilanes, constituting a unique C(sp³ )-H transformation based on a 1,5-palladium migration process.

Microwave-Assisted Palladium-Catalyzed Cross-Coupling Reactions: Generation of Carbon–Carbon Bond

Cross-coupling reactions furnishing carbon–carbon (C–C) bond is one of the most challenging tasks in organic syntheses. The early developed reaction protocols by Negishi, Heck, Kumada, Sonogashira, Stille, Suzuki, and Hiyama, utilizing palladium or its salts as catalysis have, for decades, attracted and inspired researchers affiliated with academia and industry. Tremendous efforts have been paid to develop and achieve more sustainable reaction conditions, such as the reduction in energy consumption by applying the microwave irradiation technique. Chemical reactions under controlled microwave conditions dramatically reduce the reaction time and therefore resulting in increase in the yield of the desired product by minimizing the formation of side products. In this review, we mainly focus on the recent advances and applications of palladium catalyzed cross-coupling carbon–carbon bond formation under microwave technology.

Highly Enantioselective Hiyama Cross-Coupling via Rh-Catalyzed Allylic Arylation of Racemic Allyl Chlorides

Highly enantioselective Hiyama cross-coupling reactions have been achieved through rhodium(I)-catalyzed dynamic kinetic asymmetric transformations between aryl siloxanes and cyclic racemic allyl halides. This process affords valuable enantiomerically enriched aryl-substituted cyclic allyl products and is compatible with heterocyclic allyl chloride electrophiles.

An Efficient Approach to Regio- and Stereodefined Fully-Substituted Alkenylsilanes by Pd-Catalyzed Allenic C(sp3 )-H Oxidation

A highly efficient palladium-catalyzed functionalization of allenylsilanes to give regio- and stereodefined fully-substituted alkenylsilanes has been developed. This oxidative coupling reaction showed good functional group compatibility with exclusive regio- and stereoselectivity. The pending olefin on the silyl group was shown to be an indispensable element for the initial allenic C(sp³ )-H bond cleavage, and performs as the directing group to control the overall selectivity. The addition of substoichiometric amounts of Et₃ N was found to increase the reaction rate leading to a higher reaction yield. The reaction can be easily scaled up and applied for the late-stage functionalization of natural products and pharmaceutical compounds, including amino acids and steroid derivatives. The newly introduced functional groups include aryl, alkynyl, and boryl groups. The highly strained four-membered ring, silacyclobutene was obtained when B₂ pin₂ was employed as the coupling partner. Mechanistic studies, including kinetic isotope effects, showed that the allenic C(sp³ )-H bond cleavage is the rate-limiting step.

Recent advances in the application of nano-catalysts for Hiyama cross-coupling reactions

This mini-review highlights the recent developments in the field of metal nanoparticle (NP) catalyzed Hiyama cross-coupling reactions.

Designing Cross-Coupling Reactions using Aryl(trialkyl)silanes

Organo(trialkyl)silanes have several advantages, including high stability, low toxicity, good solubility, easy handling, and ready availability compared with heteroatom-substituted silanes. However, methods for the cross-coupling of organo(trialkyl)silanes are limited, most probably because of their exceeding robustness. Thus, a practical method for the cross-coupling of organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses how aryl(trialkyl)silanes can be used in cross-coupling reactions. A pioneering example is Cu^II catalytic conditions with the use of electron-accepting aryl- or heteroaryl(triethyl)silanes and aryl iodides. The reaction forms biaryls or teraryls. This design concept can be extended to Pd/Cu^II -catalyzed cross-coupling polymerization reactions between such silanes and aryl bromides or chlorides and to Cu^I -catalyzed alkylation using alkyl halides.

One-Pot Tandem Hiyama Alkynylation/Cyclizations by Palladium(II) Acyclic Diaminocarbene (ADC) Complexes Yielding Biologically Relevant Benzofuran Scaffolds

A series of palladium acyclic diaminocarbene (ADC) complexes of the type cis-[(R¹NH)(R²)methylidene]PdCl₂(CNR¹) [R¹ = 2,4,6-(CH₃)₃C₆H₂: R² = NC₅H₁₀ (2); NC₄H₈ (3); NC₄H₈O (4)] were used not only to perform the C_sp² -C_sp Hiyama coupling between aryl iodide and triethoxysilylalkynes but also to subsequently carry out the one-pot tandem Hiyama alkynylation/cyclization reaction between 2-iodophenol and triethoxysilylalkynes, giving a convenient time-efficient access to the biologically relevant benzofuran compounds. The palladium ADC complexes (2-4) were conveniently synthesized by the nucleophilic addition of secondary amines, namely, piperidine, pyrrolidine, and morpholine on the cis-{(2,4,6-(CH₃)₃C₆H₂)NC}₂PdCl₂ in moderate yields (ca. 61-66%).