Silicon-Stereogenic Monohydrosilane: Synthesis and Applications

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.

Intramolecular Hosomi-Sakurai Reaction for the Synthesis of Benzoxasiloles

A Lewis acid-catalyzed intramolecular Hosomi-Sakurai reaction of o-(allylsilyl)benzaldehyde/ketone has been developed. The reaction proceeds through simultaneous C-Si bond cleavage and C-C bond reconstruction. This protocol provides a rapid approach for the synthesis of allyl-substituted benzoxasiloles under mild conditions.

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.

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

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.

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.

Catalytic Asymmetric Dehydrogenative Si-H/N-H Coupling: Synthesis of Silicon-Stereogenic Silazanes

Despite growing progress in the construction of silazanes, the catalytic asymmetric synthesis of silicon-stereogenic silazanes is significantly less explored and remains a considerable challenge. Herein, we report a highly enantioselective synthesis of silicon-stereogenic silazanes via catalytic dehydrogenative coupling of dihydrosilanes with anilines. The reaction readily produces a wide range of chiral silazanes and bis-silazanes in excellent yields and stereoselectivities (up to 99% ee). Further utility of this process is demonstrated by the construction of polycarbosilazanes featuring configurational main chain silicon-stereogenic chirality. In addition, the straightforward transformation of the enantioenriched silazanes delivers various chiral silane compounds in a stereospecific fashion, illustrating their potential utilities as synthons for the synthesis of novel silicon-containing functional molecules.

Organocatalytic DYKAT of Si-Stereogenic Silanes

Chiral organosilanes do not exist in nature and are therefore absent from the "chiral pool". As a consequence, synthetic approaches toward enantiopure silanes, stereogenic at silicon, are rather limited. While catalytic asymmetric desymmetrization reactions of symmetric organosilicon compounds have been developed, the utilization of racemic silanes in a dynamic kinetic asymmetric transformation (DYKAT) or dynamic kinetic resolution (DKR) would significantly expand the breadth of accessible Si-stereogenic compounds. We now report a DYKAT of racemic allyl silanes enabled by strong and confined imidodiphosphorimidate (IDPi) catalysts, providing access to Si-stereogenic silyl ethers. The products of this reaction are easily converted into useful enantiopure monohydrosilanes. We propose a spectroscopically and experimentally supported mechanism involving the epimerization of a catalyst-bound intermediate.

Chiral Silanols: Strategies and Tactics for Their Synthesis

Silanols are valuable and important compounds, which have found widespread applications in the field of materials science, synthetic chemistry, and medicinal chemistry. Although a handful of approaches have been developed for the synthesis of various silanols, access to enantioenriched silicon-stereogenic silanols remains underdeveloped. This Concept article intends to summarize and highlight recent advances in the construction of silicon-stereogenic silanols and endeavors to encourage further research in this area.

Rhodium-Catalyzed Dynamic Kinetic Asymmetric Hydrosilylation to Access Silicon-Stereogenic Center

Strategies on the construction of enantiomerically pure silicon-stereogenic silanes generally relies on desymmetrization of prochiral and symmetric substrates. However, dynamic kinetic asymmetric transformations of organosilicon compounds have remained underdeveloped and unforeseen owing to a lack of an effective method for deracemization of the static silicon stereocenters. Here we report the first Rh-catalyzed dynamic kinetic asymmetric intramolecular hydrosilylation (DyKAH) with "silicon-centered" racemic hydrosilanes that enables the facile preparation of silicon-stereogenic benzosiloles in good yields and excellent enantioselectivities. The special rhodium catalyst controlled by non-diastereopure-type mixed phosphine-phosphoramidite ligand with axial chirality and multiple stereocenters can induce enantioselectivity efficiently in this novel DyKAH reaction. Density functional theory (DFT) calculations suggest that the amide moiety in chiral ligand plays important role in facilitating the S_N 2 substitution of chloride ion to realize the chiral inversion of silicon center.

Construction of C(sp2)-Si Bonds via Ligand-Promoted C-C Bonds Cleavage of Unstrained Ketones

Herein, we report an efficient palladium-catalyzed silylation of aryl and alkenyl ketones via C-C bond cleavage and C-Si bond formation. This protocol features high efficiency and broad substrate scope. Further applications in the late-stage diversification of biologically important molecules demonstrate the synthetic utility of this method.

Copper-Catalyzed Enantioselective Hydrosilylation of Allenes to Access Axially Chiral (Cyclohexylidene)ethyl Silanes

A novel strategy of copper-catalyzed regio- and enantioselective hydrosilylation of 4-substituted vinylidenecyclohexanes with silanes was developed. In this protocol, various allenes and silanes were used to afford the corresponding (cyclohexylidene)ethyl silanes in moderate to high yields with good enantioselectivities.