Organosilicon Molecules with Medicinal Applications

Electroreductive Cross-Coupling between Aromatic Aldehydes and Chlorosilanes Enabling the Synthesis of α-Silyl Alcohols

α-Silyl alcohols are powerful structural motifs for pharmaceutical chemistry, materials chemistry, and organic synthesis. The limitations of current synthetic techniques encompass a requirement for difficult-to-obtain silyl precursors, noble-metal catalysts, and narrow substrate scopes. Here, we developed a general synthetic method for α-silyl alcohols through electroreductive cross-coupling of aldehydes and chlorosilane. This method features easily available reagents, mild conditions, and a wide substrate scope. The establishment of this protocol will provide an alternative for access to α-silyl alcohols.

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

Ruthenium-Catalyzed Sequential Hydrosilylation/Dehydrogenation and C-H Silylation: Synthesis of Six-Membered Indole Silacycles and Pyrrole Silyl Ether Cycles

Selective dehydrogenative C-H silylation is one of the most powerful tools to synthesize silacycles. Herein, we developed Ru-catalyzed sequential hydrosilylation/C-H silylation of allyl-indoles and dehydrogenative O-H/C-H silylation of pyrrole phenols. Both six-membered indole silacycles and pyrrole silyl ether cycles were successfully synthesized with good functional group tolerance. Furthermore, the RuHCl(CO)(PPh3)3 catalyst exhibited high reaction compatibility in hydrosilylation of alkene, dehydrogenative O-H silylation, and C-H silylation.

An SN1-Approach to Cross-Coupling: Deoxygenative Arylation Facilitated by the β-Silicon Effect

We report a dual metal-catalyzed method for the cross-coupling of unprotected alcohols by exploiting the β-Si effect. This deoxygenative Suzuki-Miyaura reaction tolerates a range of primary, secondary, and tertiary alcohol substrates along with diverse functional groups and heterocycles. Mechanistic experiments including KIE, VTNA, and Eyring analyses suggest the existence of a carbocation intermediate on the reaction pathway, consistent with a rare SN1 pathway for the activation of an electrophile in cross-coupling reactions. A novel bis-imidazolium N-heterocyclic carbene (NHC) ligand was found to be optimal for reactivity, and nickel(0)-, nickel(I)- and nickel(II)- complexes of this ligand were isolated and characterized. In contrast to more well-established shorter chain ligands, these long-chain NHCs are found to have characteristically large bite angles, which may be critical for enabling the deoxygenative arylation of aliphatic alcohols.

Organophotocatalyzed Cross Coupling of C- and Si-Radical to Access Dibenzylic Silanes from para-Quinone Methides and Silanecarboxylic Acids

Herein we present a catalytic cross-coupling strategy between C-radicals and Si-radicals, enabling the efficient, gentle, and versatile synthesis of dibenzylic silanes from para-quinone methides and silanecarboxylic acids as the stable silyl radical precursors. The reaction is facilitated by an inexpensive organophotocatalyst and exhibits broad compatibility with various electron-donating and electron-withdrawing functional groups. Notably, mechanistic investigations suggest the involvement of dibenzylic and silyl radicals, underscoring a novel radical coupling mechanism that introduces a fresh perspective on C-Si bond formation.

Making Full Use of TMSCF3: Deoxygenative Trifluoromethylation/Silylation of Amides

As one of the most powerful trifluoromethylation reagents, (trifluoromethyl)trimethylsilane (TMSCF3) has been widely used for the synthesis of fluorine-containing molecules. However, to the best of our knowledge, the simultaneous incorporation of both TMS- and CF3- groups of this reagent onto the same carbon of the products has not been realized. Herein, we report an unprecedented SmI2/Sm promoted deoxygenative difunctionalization of amides with TMSCF3, in which both silyl and trifluoromethyl groups are incorporated into the final product, yielding α-silyl-α-trifluoromethyl amines with high efficiency. Notably, the silyl group could be further transformed into other functional groups, providing a new method for the synthesis of α-quaternary α-CF3-amines.

Organocatalytic asymmetric synthesis of Si-stereogenic silacycles

A strong and confined Brønsted acid catalyzed enantioselective cyclization of bis(methallyl)silanes provides enantioenriched Si-stereogenic silacycles. High enantioselectivities of up to 96.5:3.5 er were obtained for a range of bis(methallyl)silanes. NMR and ESI-MS studies reveal that the formation of a covalent adduct irreversibly inhibits turnover. Remarkably, we found that acetic acid as an additive promotes the collapse of this adduct, enabling full turnover. Experimental investigation and density functional theory (DFT) calculations were conducted to elucidate the origin of this phenomenon and the observed enantioselectivity.

Synthesis of unsymmetrical dialkoxydiarylsilanes and diarylsilanediols from tetraalkoxysilane having a dioxasilepane unit

The tetraalkoxysilane carrying a stable seven-membered dioxasilepane moiety and two trifluoroethoxy groups undergoes reliable iterative substitution of the two trifluoroethoxy groups by sequential treatment with different aryl Grignard reagents while keeping the seven-membered structure intact. The process results in the synthesis of unsymmetrical dialkoxydiarylsilanes and eventually diarylsilanediols after proper hydrolysis.

Enantioselective Aminosilylation of Alkenes by Palladium/Ming-Phos-Catalyzed Tandem Narasaka-Heck/Silylation Reaction

A Pd-catalyzed enantioselective aminosilylation of alkenes via tandem Aza-Heck/silylation reaction under Pd/Sadphos catalysis is disclosed. A wide array of oxime esters and silicon reagents are tolerated, furnishing the chiral pyrrolines bearing one quaternary or two contiguous stereocenters in good yield with high enantioselectivity. Not only terminal alkenes but also tri-substituented internal alkenes successfully participate in the reaction, delivering vicinal stereocenters in complete diastereoselectivity and high enantioselectivity. DFT study is conducted to probe the reaction pathway and the origin of the enantioselectivity, which revealed that the stereoinduction arises from the weak interaction between the aromatic ring of the substrate fragment and naphthyl group in the ligand.

Palladium(II)-Catalyzed Norbornene-Mediated Selective meta-C-H Silylation for the Synthesis of Arylsilanes from Primary Benzamides

A palladium(II)-catalyzed norbornene-mediated remote selective meta-C-H silylation of primary benzamides was developed for the synthesis of arylsilanes. Such a conversion provides access to a range of arylsilanes with exclusive selectivity using norbornene (NBE) as the meta-C-H activator. The amide directing group can be detached simultaneously through C-C bond cleavage or undergo a dehydration reaction pathway to form nitriles.

Dehydrogenative oxidation of hydrosilanes using gold nanoparticle deposited on citric acid-modified fibrillated cellulose: unveiling the role of molecular oxygen

Efficient and environmentally friendly synthesis of silanols is a crucial issue across the broad fields of academic and industrial chemistry. Herein, we describe the dehydrogenative oxidation of hydrosilane using a gold nanoparticle catalyst supported by fibrillated citric acid-modified cellulose (F-CAC). Au:F-CAC catalysts with various particle sizes (1.7 nm, 4.9 nm, and 7.7 nm) were prepared using the trans-deposition method, a technique previously reported by our group. These catalysts exhibited significant catalytic activity to produce silanols with high turnover frequency (TOF) of up to 7028 h-1. Recycling experiments and transmission electron microscopy (TEM) observation represented the high durability of Au:F-CAC under the reaction conditions, allowing kinetic studies on size dependency. Mechanistic studies were conducted, including isotope labelling experiments, kinetics, and various spectroscopies. Notably, the near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) of the model catalyst (Au:PVP) revealed the formation of catalytically active cationic Au sites on the surface through the adsorption of molecular oxygen, providing a new insight into the reaction mechanism.

Nickel-Catalyzed Intramolecular Hydrosilylation of Alkynes: Embracing Conventional and Electrochemical Routes

Nickel-catalyzed intramolecular hydrosilylation can be efficiently achieved with high regio- and stereoselectivities through two distinct methodologies. The first approach utilizes a conventional method, involving the reduction of nickel salt (NiBr2-2,2'-bipyridine) using manganese metal. The second method employs a one-step electrochemical reaction, utilizing the sacrificial anode process and NiBr2bipy catalysis. Both methods yield silylated heterocycles in good to high yields through a syn-exo-dig cyclization process. Control experiments and molecular electrochemistry (cyclic voltammetry) provided further insights into the reaction mechanism.

Divergent Synthesis of Enantioenriched Silicon-Stereogenic Benzyl-, Vinyl- and Borylsilanes via Asymmetric Aryl to Alkyl 1,5-Palladium Migration

Functionalization of Si-bound methyl group provides an efficient access to diverse organosilanes. However, the asymmetric construction of silicon-stereogenic architectures by functionalization of Si-bound methyl group has not yet been described despite recent significant progress in producing chiral silicon. Herein, we disclosed the enantioselective silylmethyl functionalization involving the aryl to alkyl 1,5-palladium migration to access diverse naphthalenes possessing an enantioenriched stereogenic silicon center, which are inaccessible before. It is worthy to note that the realization of asymmetric induction at the step of metal migration itself remains challenging. Our study constitutes the first enantioselective aryl to alkyl 1,5-palladium migration reaction. The key to the success is the discovery and fine-tuning of the different substituents of α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-based phosphoramidites, which ensure the enantioselectivity and desired reactivity.

Catalytic Kinetic Resolution of Monohydrosilanes via Rhodium-Catalyzed Enantioselective Intramolecular Hydrosilylation

The catalytic access of silicon-stereogenic organosilanes remains a big challenge, and largely depends on the desymmetrization of the symmetric precursors with two identical substitutes attached to silicon atom. Here we report the construction of silicon-stereogenic organosilanes via catalytic kinetic resolution of racemic monohydrosilanes with good to excellent selectivity factors. Both Si-stereogenic dihydrobenzosiloles and Si-stereogenic monohydrosilanes could be efficiently accessed in one single operation via Rh-catalyzed enantioselective intramolecular hydrosilylation, employing (R,R)-Et-DuPhos as the optimal ligand. This catalytic protocol features mild conditions, a low catalyst loading (0.1 mol % [Rh(cod)Cl]2), high stereoinduction (S factor up to 152), and excellent scalability. Moreover, further derivatizations led to the efficient synthesis of uncommon middle-size (7- and 8-membered) Si-stereogenic silacycles. Preliminary mechanistic study indicates this reaction might undergo a modified Chalk-Harrod mechanism.

SilE-R and SilE-S-DABB Proteins Catalying Enantiospecific Hydrolysis of Organosilyl Ethers

Silyl ethers fulfil a fundamental role in synthetic organic chemistry as protecting groups and their selective cleavage is an important factor in their application. We present here for the first time two enzymes, SilE-R and SilE-S, which are able to hydrolyse silyl ethers. They belong to the stress-response dimeric A/B barrel domain (DABB) family and are able to cleave the Si-O bond with opposite enantiopreference. Silyl ethers containing aromatic, cyclic or aliphatic alcohols and, depending on the alcohol moiety, silyl functions as large as TBDMS are accepted. The X-ray crystal structure of SilE-R, determined to a resolution of 1.98 Å, in combination with mutational studies, revealed an active site featuring two histidine residues, H8 and H79, which likely act synergistically as nucleophile and Brønsted base in the hydrolytic mechanism, which has not previously been described for enzymes. Although the natural function of SilE-R and SilE-S is unknown, we propose that these 'silyl etherases' may have significant potential for synthetic applications.

Investigation of unexpected silane ions caused by gas-phase reactions in Orbitrap gas chromatography-mass spectrometry

RATIONALE

The mass spectra of compounds containing dimethyl (phenyl)silyl group (-SiMe2Ph) sometimes exhibit unusual ion peaks when measured using Orbitrap gas chromatography-mass spectrometry (GC-MS). This would complicate the mass spectra and may limit the matching of spectral data with preexisting resources for compound annotation. These peaks were identified as products from reactions with residual water.

METHODS

A series of dimethyl (phenyl)silyl compounds were dissolved in methanol and investigated using Orbitrap GC-MS. Certain ions reacted with residual water in the C-trap. The reaction was confirmed using accurate mass and elemental composition analysis via MS studies, and the active center of the reaction was determined using density functional theory (DFT) calculations.

RESULTS

Two types of gas-phase reactions between gaseous water and cations from a series of silanes were identified. DFT calculations indicate that silicon (Si) acts as the active center for these gas-phase water reactions. Compounds with multiple Si atoms generate a larger number of additional ions, which would complicate the mass spectra. The mass spectra of vinylsilanes and alkylsilanes with -SiMe2Ph indicate that the conjugated group linked to -SiMe2Ph can affect the water adduction process.

CONCLUSIONS

Silane ions could react with residual water in the C-trap of an Orbitrap mass spectrometer. The mass spectra of these compounds may exhibit unexplained peaks arising from gas-phase reactions. Although these reactions may decrease spectral matching scores for compound annotation, they offer opportunities for systematic investigations into the mechanistic and kinetic aspects of high-energy ion reactivity.

Hydroboration of vinylsilanes providing diversity-oriented hydrophobic building blocks for biofunctional molecules

Hydroboration of vinylsilanes with BH3 affords two silylethanol regioisomers. Herein, we investigated the regioisomeric ratio of hydroboration products from various vinylsilanes, focusing on the characteristic reaction profile. All investigated vinylsilanes afforded both regioisomers, and greater bulkiness increased the proportion of the Markovnikov products. The obtained silylethanols were used as hydrophobic building blocks for constructing nuclear progesterone receptor (PR) modulators. Notably, structural conversions from an α-isomer (silylethan-1-oxy derivative) to a β-isomer (2-silylethoxy derivative) caused complete activity-switching from a PR agonist to an antagonist. Our results indicate that silylethanols are useful for structural development, and vinylsilanes are a versatile source of hydrophobic building blocks for obtaining biofunctional molecules.

Catalytic Access to Diastereometrically Pure Four- and Five-Membered Silyl-Heterocycles Using Transborylation

Silyl-heterocycles offer a unique handle to expand and explore chemical space, reactivity, and functionality. The shortage of catalytic methods for the preparation of diverse and functionalized silyl-heterocycles however limits widespread exploration and exploitation. Herein the borane-catalyzed intramolecular 1,1-carboboration of silyl-alkynes has been developed for the synthesis of 2,3-dihydrosilolyl and silylcyclobut-2-enyl boronic esters. Successful, catalytic carboboration has been achieved on a variety of functionally diverse silyl-alkynes, using a borane catalyst and transborylation-enabled turnover. Mechanistic studies, including 13C-labelling, computational studies, and single-turnover experiments, suggest a reaction pathway proceeding by 1,2-hydroboration, 1,1-carboboration, and transborylation to release the alkenyl boronic ester product and regenerate the borane catalyst.

Silylation and (Hetero)aryl/alkenylation of Unactivated Alkenes via Radical-Mediated Distal 1,4-Migration with Hydrosilanes under Organophotocatalysis

We report a novel organic photoredox catalysis to achieve unprecedented γ-(hetero)aryl/alkenyl-δ-silyl aliphatic amines via silyl-mediated distal (hetero)aryl/alkenyl migration of aromatic/alkenyl amines bearing unactivated alkenes with hydrosilanes. This protocol features mild and metal-free reaction conditions, high atom economy, excellent selectivity, and functional group compatibility. Mechanistic studies suggest that silylation and (hetero)aryl/alkenylation involve photoredox hydrogen atom transfer catalysis and subsequent 1,4-migration of a remote (hetero)aryl/alkenyl group from nitrogen to carbon.

Cobalt-catalyzed cross-electrophile coupling of alkynyl sulfides with unactivated chlorosilanes

Herein, we disclose a highly efficient cobalt-catalyzed cross-electrophile alkynylation of a broad range of unactivated chlorosilanes with alkynyl sulfides as a stable and practical alkynyl electrophiles. Strategically, employing easily synthesized alkynyl sulfides as alkynyl precursors allows access to various alkynylsilanes in good to excellent yields. Notably, this method avoids the utilization of strong bases, noble metal catalysts, high temperature and forcing reaction conditions, thus presenting apparent advantages, such as broad substrate scope (72 examples, up to 97% yield), high Csp-S chemo-selectivity and excellent functional group compatibility (Ar-X, X = Cl, Br, I, OTf, OTs). Moreover, the utilities of this method are also illustrated by downstream transformations and late-stage modification of structurally complex natural products and pharmaceuticals. Mechanistic studies elucidated that the cobalt catalyst initially reacted with alkynyl sulfides, and the activation of chlorosilanes occurred via an SN2 process instead of a radical pathway.

Nickel/photoredox-catalyzed three-component silylacylation of acrylates via chlorine photoelimination

The extensive utility of organosilicon compounds across a wide range of disciplines has sparked significant interest in their efficient synthesis. Although catalytic 1,2-silyldifunctionalization of alkenes provides a promising method for the assembly of intricate organosilicon frameworks with atom and step economy, its advancement is hindered by the requirement of an external hydrogen atom transfer (HAT) agent in photoredox catalysis. Herein, we disclose an efficient three-component silylacylation of α,β-unsaturated carbonyl compounds, leveraging a synergistic nickel/photoredox catalysis with various hydrosilanes and aroyl chlorides. This method enables the direct conversion of acrylates into valuable building blocks that contain both carbonyl and silicon functionalities through a single, redox-neutral process. Key to this reaction is the precise activation of the Si-H bond, achieved through chlorine radical-induced HAT, enabled by the photoelimination of a Ni-Cl bond. Acyl chlorides serve a dual role, functioning as both acylating agents and chloride donors. Our methodology is distinguished by its mild conditions and extensive substrate adaptability, significantly enhancing the late-stage functionalization of pharmaceuticals.

Silver-Promoted Rapid Synthesis of 3-Arylindan-1-ones: Microwave-Assisted Reductive Coupling of N-Tosylhydrazone and Boronic Acids

An efficient and straightforward one-pot tandem synthesis of 3-arylindan-1-ones was consummated through silver nitrate-promoted C-C coupling of simple indane-1,3-dione with arylboronic acid via 1,3-indanedione monotosylhydrazone under microwave conditions. The resulting series of 3-arylindan-1-ones exhibited impressive yields, surpassing those achievable with traditional methods and requiring a shorter time frame. This innovative approach significantly accelerated the synthesis of biologically active compounds such as (+)-indatraline (Lu 19-005) and several other industrially relevant substances.

Synthesis of Functionalized Organosilicon Compounds/Distal Ketones via Ring-Opening Giese Addition of Cycloalkanols under Organophotocatalytic Conditions

Visible-light-induced organophotocatalyzed ring-opening followed by remote Giese addition of tertiary cycloalkanols with β-silylmethylene malonates has been developed under mild reaction conditions for the synthesis of organosilicon compounds, bearing a ketone group distally substituted with a silyl group with an additional dialkyl malonate functional handle in moderate to good yields (34-72%). The protocol also worked well with diverse Michael acceptors, such as alkylidene/benzylidene malonates, trifluoro methylidene malonate, benzylidene malononitrile, α-cyano-enone, and α-cyano vinyl sulfone, and delivered desired valuable distally functionalized ketones. To showcase the potential of the method, various synthetic transformations of the obtained product were also demonstrated.

Photoredox Synthesis of Silicon-Containing Isoindolin-1-ones and Deuterated Analogues Through Hydrosilylation and Deuterium-silylation

An efficient, practical, and metal-free protocol for the synthesis of silicon-containing isoindolin-1-ones and deuterated analogues via the synergistic combination of an organic photoredox and hydrogen atom transfer process is described. This strategy features mild reaction conditions, high atom economy, and excellent functional group compatibility, delivering a myriad of structurally diverse and valuable products with good to excellent yields.

Enantioselective and Regiodivergent Synthesis of Propargyl- and Allenylsilanes through Catalytic Propargylic C-H Deprotonation

We report a highly enantioselective intermolecular C-H bond silylation catalyzed by a phosphoramidite-ligated iridium catalyst. Under reagent-controlled protocols, propargylsilanes resulting from C(sp3)-H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less-hindered site was also observed. A variety of electrophilic silyl sources (R3SiOTf and R3SiNTf2), either commercial or in situ-generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, 1,3-enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η3-propargyl/allenyl Ir intermediate is generated upon π-complexation-assisted deprotonation and undergoes outer-sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step.

Radical cascade silylation/cyclization of 1,7-dienes to access silyl-substituted benzo[b]azepin-2-ones

A novel silyl radical-induced cascade silylation/cyclization of 1,7-dienes has been realized employing readily available hydrosilanes as a silicon source and Cu(I) salt as a catalyst. This protocol introduces diverse silicon fragments into a challenging 7-membered ring structure and provides an efficient approach to a wide array of biologically important silyl-substituted benzo[b]azepin-2-ones. Several control experiments suggest that the reaction undergoes a free radical process. The gram-scale synthesis and late-stage transformations further demonstrate the scalability and applicability of the reaction in organic synthesis.

Late-Stage Diversification of Phosphines by C-H Activation: A Robust Strategy for Ligand Design and Preparation

ConspectusThe advent of the twenty-first century marked a golden era in the realm of synthetic chemistry, exemplified by groundbreaking advancements in the field of C-H activation, which is a concept that quickly transitioned from mere academic fascination to an essential element within the synthetic chemist's toolkit. This methodological breakthrough has given rise to a wealth of opportunities spanning a wide range of chemical disciplines. It has facilitated the late-stage diversification of elaborate organic frameworks, encompassing the spectrum from simple methane to complex polymers, thus refining the lead optimization process and easing the production of diverse molecular analogues. Among these strides forward, the development of phosphorus(III)-directed C-H activation stands out as an increasingly significant and inventive approach for the design and synthesis of ligands, substantially redefining the contours of synthetic methodology.Phosphines, renowned for their roles as ligands and organocatalysts, have become fundamentally important in modern organic chemistry. Their efficiency as ligands is significantly affected by coordination with transition metals, which is essential for their involvement in catalytic processes, influencing both the catalytic activity and the selectivity. Historically, the fabrication of phosphines predominantly relied on synthesis employing complex, multistep procedures. Addressing this limitation, our research has delved into ligand design and synthesis through innovative catalytic P(III)-directed C-H activation strategies. In this Account, we have explored a spectrum of procedures, including direct arylation using metal catalysis, and ventured further into domains such as C-H alkylation, alkenylation, aminocarbonylation, alkynylation, borylation, and silylation. These advances have enriched the field by providing efficient methods for the late-stage diversification of biaryl-type monophosphines as well as enabled the C-H activation of triphenylphosphine and its derivatives. Moreover, we have successfully constructed libraries of diverse axially chiral binaphthyl phosphine ligands, showcasing their potency in asymmetric catalysis. Through this Account, we aim to illuminate the exciting possibilities presented by P(III)-directed C-H activation in propelling the boundaries of organic synthesis. By highlighting our pioneering work, we hope to inspire further developments in this promising field of chemistry.

Congested C(sp3)-rich architectures enabled by iron-catalysed conjunctive alkylation

Catalytic cross-coupling by transition metals has revolutionized the formation of C-C bonds in organic synthesis. However, the challenge of forming multiple alkyl-alkyl bonds in crowded environments remains largely unresolved. Here, we report the regioselective functionalization of olefins with sp3-hybridized organohalides and organozinc reagents using a simple (terpyridine)iron catalyst. Aliphatic groups of various sizes are successfully installed on either olefinic carbon, furnishing a diverse array of products with congested cores featuring C- or heteroatom-substituted stereocenters. The method enables access to valuable but synthetically challenging C(sp3)-rich molecules, including alicyclic compounds bearing multiple contiguous stereocenters through annulation cascades. Mechanistic and theoretical studies suggest a stepwise iron-mediated radical carbometallation pathway followed by outer-sphere C-C bond formation, which potentially opens the door to a broader scope of transformations and new chemical space.

Nickel-Catalyzed Reductive Cross-Coupling of Propargylic Acetates with Chloro(vinyl)silanes: Access to Silylallenes

Because of their various reactivities, propargyl acetates are refined chemical intermediates that are extensively applied in pharmaceutical synthesis. Currently, reactions between propargyl acetates and chlorosilanes may be the most effective method for synthesizing silylallenes. Nevertheless, owing to the adaptability and selectivity of substrates, transition metal catalysis is difficult to achieve. Herein, nickel-catalyzed reductive cross-coupling reactions between propargyl acetates and substituted vinyl chlorosilanes for the synthesis of tetrasubstituted silylallenes are described. Therein, metallic zinc is a crucial reductant that effectively enables two electrophilic reagents to selectively construct C(sp2)-Si bonds. Additionally, a Ni-catalyzed reductive mechanism involving a radical process is proposed on the basis of deuteration-labeled experiments.

Palladium/NBE-Catalyzed Regioselective C-H Silylation: Access to Divergent Silicon-Containing Indoles

A palladium/norbornene (NBE)-catalyzed regioselective C-H silylation of free NH-indoles is reported. This protocol uses Pd(OAc)2 as the catalyst and Cu(OAc)2 as the oxidant, and the reaction relies on the control of NBE as a switch. The reaction tolerates various functional groups, and a series of silicon-containing indoles were directly synthesized in 30%-94% yields.

Selective Access to Silacyclopentanes and Homoallylsilanes by La-Catalyzed Hydrosilylations of 1-Aryl Methylenecyclopropanes

Methylenecyclopropanes (MCPs) have emerged as versatile building blocks in synthetic chemistry because of their unique reactivity. However, metal-catalyzed hydrosilylation of MCPs has met with very limited successes. In this paper, catalytic selective hydrosilylations of MCPs with some primary silanes using an ene-diamido lanthanum ate complex as the catalyst were described. The catalytic reactions resulted in the selective formation of silacyclopentanes and (E)-homoallylsilanes, respectively, depending on the substituents on MCPs. The formation of silacyclopentanes via a catalytic cascade inter- and intramolecular hydrosilylation mechanism is strongly supported by the control and deuteration-labeling experiments and DFT calculations. The unique reactivity and selectivity could be attributed to the large lanthanum ion and ate structure of the catalyst.

Copper-Catalyzed Asymmetric Synthesis of Silicon-Stereogenic Benzoxasiloles

A Cu-catalyzed asymmetric synthesis of silicon-stereogenic benzoxasiloles has been realized via intramolecular Si-O coupling of [2-(hydroxymethyl)phenyl]silanes. Cu(I)/difluorphos is found to be an efficient catalytic system for enantioselective Si-C bond cleavage and Si-O bond formation. In addition, kinetic resolution of racemic substituted [2-(hydroxymethyl)phenyl]silanes using Cu(I)/ PyrOx (pyridine-oxazoline ligands) as the catalytic system is developed to afford carbon- and silicon-stereogenic benzoxasiloles. Ring-opening reactions of chiral benzoxasiloles with organolithiums and Grignard reagents yield various enantioenriched functionalized tetraorganosilanes.

Silyl Radical Generation from Silylboronic Pinacol Esters through Substitution with Aminyl Radicals

A novel strategy was developed to generate silyl radicals from silylboronic pinacol esters (SPEs) through nucleohomolytic substitution of boron with aminyl radicals. We successfully applied this strategy to obtain diverse organosilicon compounds using SPEs and N-nitrosamines under photoirradiation without any catalyst. The ability to access silyl radicals offers a new perspective for chemists to rapidly construct Si-X bonds.

Silylation of 2H-indazoles by photoinduced hydrogen atom transfer catalysis

A metal-free, visible-light-mediated C-H silylation of 2H-indazoles with triphenylsilane has been developed employing 4CzIPN as a photocatalyst and triisopropylsilanethiol as a hydrogen atom transfer (HAT) reagent under aerobic reaction conditions. This method shows tolerance toward many functional groups and affords a variety of silylated indazoles at up to 89% yield. The experimental results suggest that the reaction progresses through a radical pathway.

Silicon-Containing Thiol-Specific Bioconjugating Reagent

A new bioconjugation reagent containing silicon has been developed for the selective reaction with thiols. The inclusion of silicon significantly improves chemoselectivity and suppresses retro processes, thereby exceeding the capabilities of traditional reagents. The method is versatile and compatible with a broad range of thiols and unsaturated carbonyl compounds and yields moderate to high results. These reactions can be conducted under biocompatible conditions, thereby making them suitable for protein bioconjugation. The resulting conjugates display good stability in the presence of various biomolecules, which suggests their potential application for the synthesis of antibody-drug conjugates. Furthermore, the presence of a silicon moiety within the conjugated products opens up new avenues for drug release and bridging inorganics with other disciplines. This new class of silicon-containing thiol-specific bioconjugation reagents has significant implications for researchers working in bioanalytical science and medicinal chemistry and leads to innovative opportunities for advancing the field of bioconjugation research and medicinal chemistry.

Organocatalytic Asymmetric Synthesis of Si-Stereogenic Siloxanols

We report the organocatalytic synthesis of Si-stereogenic compounds via desymmetrization of a prochiral silanediol with a chiral imidazole-containing catalyst. This metal-free silylation method affords high yields with enantioselectivity up to 98:2 for various silanediol and silyl chloride substrate combinations (including secondary alkyl, vinyl, and H groups), accessing products with potential for further elaboration. NMR and X-ray studies reveal insight into the H-bonding interactions between the imidazole organocatalyst and the silanediol and the dual activating role of the Lewis basic imidazole to account for the high enantioselectivity.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Catalytic Synthesis of Silanols by Hydroxylation of Hydrosilanes: From Chemoselectivity to Enantioselectivity

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non-natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon-stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon-stereogenic silanols from dihydrosilanes.

Rhodium-Catalyzed Enantioselective Formal [4+1] Cyclization of Benzyl Alcohols and Benzaldimines: Facile Access to Silicon-Stereogenic Heterocycles

The carbon-to-silicon switch in formation of bioactive sila-heterocycles with a silicon-stereogenic center has garnered significant interest in drug discovery. However, metal-catalyzed synthesis of such scaffolds is still in its infancy. Herein, a rhodium-catalyzed enantioselective formal [4+1] cyclization of benzyl alcohols and benzaldimines has been realized by enantioselective difunctionalization of a secondary silane reagent, affording chiral-at-silicon cyclic silyl ethers and sila-isoindolines, respectively. Mechanistic studies reveal a dual role of the rhodium-hydride catalyst. The coupling system proceeds via rhodium-catalyzed enantio-determining dehydrogenative OH silylation of the benzyl alcohol or hydrosilylation of the imine to give an enantioenriched silyl ether or silazane intermediate, respectively. The same rhodium catalyst also enables subsequent intramolecular cyclative C-H silylation directed by the pendent Si-H group. Experimental and DFT studies have been conducted to explore the mechanism of the OH bond silylation of benzyl alcohol, where the Si-O reductive elimination from a Rh(III) hydride intermediate has been established as the enantiodetermining step.

Palladium-Catalyzed Skeletal Rearrangement of Substituted 2-Silylaryl Triflates via 1,5-C-Pd/C-Si Bond Exchange

A palladium-catalyzed skeletal rearrangement of 2-(2-allylarylsilyl)aryl triflates has been developed to give highly fused tetrahydrophenanthrosilole derivatives via unprecedented 1,5-C-Pd/C-Si bond exchange. The reaction pathways can be switched toward 4-membered ring-forming C(sp2 )-H alkylation by tuning the reaction conditions to give completely different products, fused dihydrodibenzosilepin derivatives, from the same starting materials. The inspection of the reaction conditions revealed the importance of carboxylates in promoting the C-Pd/C-Si bond exchange.

Novel Acaricidal Silico-Containing Pyrazolyl Acrylonitrile Derivatives Identified through Rational Carbon-Silicon Bioisosteric Replacement Strategy

The identification of novel pyrazolyl acrylonitrile acaricides with improved properties is of great value for the control of phytophagous mites. A series of innovative silicon-containing pyrazolyl acrylonitriles were rationally designed by applying a bioisosteric carbon-silicon replacement strategy and prepared based on novel synthetic methodology. As a result of our research, we discovered compound A25 which possesses outstanding acaricidal activity. With an LC50 value of 0.062 mg/L, compound A25 was found to be 2.3-fold and 1.9-fold more potent than the commercial acaricides cyenopyrafen and cyetpyrafen, respectively. Enzymatic inhibitory assay indicated that the active principle M1 of compound A25 possesses an IC50 value of 2.32 μM against Tetranychus cinnabarinus SDH, which was about twofold superior compared to the active metabolites of cyenopyrafen (IC50 = 4.72 μM). Molecular docking study showed that the active metabolites 2 and 3 and their corresponding silicon counterparts form H-bonds and cation-π interaction with the residues of Trp165, Tyr433, and Arg279.

Ligand-modulated nickel-catalyzed regioselective silylalkylation of alkenes

Organosilicon compounds have shown tremendous potential in drug discovery and their synthesis stimulates wide interest. Multicomponent cross-coupling of alkenes with silicon reagents is used to yield complex silicon-containing compounds from readily accessible feedstock chemicals but the reaction with simple alkenes remains challenging. Here, we report a regioselective silylalkylation of simple alkenes, which is enabled by using a stable Ni(II) salt and an inexpensive trans-1,2-diaminocyclohexane ligand as a catalyst. Remarkably, this reaction can tolerate a broad range of olefins bearing various functional groups, including alcohol, ester, amides and ethers, thus it allows for the efficient and selective assembly of a diverse range of bifunctional organosilicon building blocks from terminal alkenes, alkyl halides and the Suginome reagent. Moreover, an expedient synthetic route toward alpha-Lipoic acid has been developed by this methodology.

Hydrosilane/Organoiodine Coupling-Enabled Studies of Organosilane Physical Properties

ConspectusThis Account summarizes recent developments in metal-mediated coupling reactions between hydrosilanes and aryl iodides in the presence of Pd(P(t-Bu)3)2 and base. Alkylated organosilanes are obtained when Pt(P(t-Bu)3)2 and a base are employed in reactions between hydrosilanes and aliphatic iodides. These transformations show unusual reactivity compared to the typical behavior of hydrosilanes toward organoiodides in the presence of PdCl2 or PtCl2, and they proceed in high yields under mild conditions. In addition, the reaction demonstrates (1) high functional group tolerances, (2) stepwise introduction of substituents onto silicon atoms from secondary silanes, and (3) transformation without cleavage of weak Si-Si σ bonds in the molecules.This transformation can serve as a powerful tool for the synthesis of functional organosilicon compounds. The advantage is the flexibility in the molecular structure due to the large size compared to carbon. These compounds have relatively sparse packing in the crystalline state, unlike π-conjugated molecules, which induce dense π-π interactions. Consequently, they have significantly different physical properties in solution and in the solid state. Among them, aromatic disilanes and oligosilanes are important substance groups, because the conjugated chain within these molecules expands due to σ-π interaction between Si-Si σ bond and π orbital of aromatic ring. σ-π Conjugation is most efficient when the dihedral angle between the aromatic ring and the Si-Si bond is 90°, resulting in the overlap of σ orbital and π orbital. The conformational structure, packing, and physical properties of these compounds can change in tandem in response to external stimuli through a crystal phase transition. The interlocking changes in structure and physical properties are reversible, easily returning to their original state with different external stimulus. This account covers several important aspects, including solid-state emission with high fluorescence intensity, aggregation-induced emission (AIE) in water-THF system, mechanochromic fluorescence, organic light emitting diode (OLED), second harmonic generation (SHG) and thermosalient phenomena.This reaction can synthesize optically active tertiary and quaternary silanes by the enantioselective arylation of secondary silanes with aryl iodides using a palladium catalyst modified with a TADDOL-derived amide phosphoric acid ester as a chiral ligand. These optically active compounds can be used as useful circularly polarized luminescence (CPL) materials due to their strong luminescence intensity (Φ) and luminescence dissymmetry factor (glum) attributed to the chiral silicon atom. The efficient synthesis of sila-pharmaceuticals using this method as a key step is also described.The technique enables the design and synthesis of various silicon-containing bioactive substances and medical chemicals. Through the synthesis of organosilane compounds using this method, it is anticipated that the development of functional organic silanes will accelerate their practical applications in a wide range of fields.

Thiol-Specific Silicon-Containing Conjugating Reagent: β-Silyl Alkynyl Carbonyl Compounds

Site-specific modification of thiol-containing biomolecules has been recognized as a versatile and powerful strategy for probing our biological systems and discovering novel therapeutics. The addition of lipophilic silicon moiety opens up new avenues for multi-disciplinary research with broad applications in both the medicinal and material sciences. However, adhering to the strict biocompatibility requirements, and achieving the introduction of labile silicon handle and high chemo-selectivity have been formidable. In this paper, we report silicon-based conjugating reagents including β-trialkylsilyl and silyl ether-tethered alkynones that selectively react with thiols under physiological conditions. The pH-neutral, metal-free and additive-free reaction yields stable products with broad substrate compatibility and full retention of silicon handles in most cases. Besides simple aliphatic and aromatic thiols, this approach is applicable in the labeling of thiols present in proteins, sugars and payloads, thereby expanding the toolbox of thiol conjugation.

Photocatalytic and Electrochemical Borylation and Silylation Reactions

Due to their high versatility borylated and silylated compounds are inevitable synthons for organic chemists. To escape the classical hydroboration/hydrosilylation paradigm, chemists turned their attention to more modern and green methods such as photoredox chemistry and electrosynthesis. This account focuses on novel methods for the generation of boryl and silyl radicals to forge C-B and C-Si bonds from our group.

Photoredox Metal-Free Synthesis of Unnatural β-Silyl-α-Amino Acids via Hydrosilylation

An efficient, practical and metal-free methodology for the synthesis of β-silyl-α-amino acid motifs via photoredox and hydrogen atom transfer (HAT) process is described. This protocol enables the direct hydrosilylation of dehydroalanine derivatives and tolerates a wide array of functional groups and synthetic handles, leading to valuable β-silyl-α-amino acids with moderate to good yields.

NBE-Controlled Palladium-Catalyzed Intermolecular Selective C-H Silylation of Boronic Acids

An efficient palladium-catalyzed intermolecular selective C-H silylation of boronic acids is described. The combination of palladium catalyst with copper oxidant enables ortho-selective C-H silylation by employing hexamethyldisilane as the trimethylsilyl source, which relies on the control of NBE derivatives as a switch, thus providing straightforward access to divergent organosilicon compounds.

Decarboxylative Allylation of Silanecarboxylic Acids Enabled by Organophotocatalysis

Herein we present a visible-light-facilitated transition-metal-free allylic silylation reaction under mild conditions. This protocol is enabled by an inexpensive organophotocatalyst and provides efficient and concise synthetic routes to substituted allylsilanes, particularly from readily available allyl sulfones and stable silanecarboxylic acids as silyl radical precursors. Further investigations reveal that this strategy is also generally compatible with vinyl sulfones to access vinylsilanes. The silver catalytic system opens up an alternative entry to realize the decarboxylative allylation of silanecarboxylic acids.

Controllable Si-C Bond Formation from Trihydrosilanes En Route to Synthesis of 1,4-Azasilinanes with Diverse Silyl Functionalities

A B(C6F5)3-catalyzed controllable inter/intra-/intermolecular Si-C bond formation process has been developed from trihydrosilane and dienamide with alkenes, anilines, or aryl iodides. A variety of 1,4-azasilinanes have been generated with diverse exo-cyclic heteroleptic disubstitutions on silicon, thereby expanding the range of silaazacyclic rings available for the discovery of silicon-containing drugs.

Disilane-bridged architectures: an emerging class of molecular materials

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.