Synergistic Ni/Cu catalyzed migratory arylsilylation of terminal olefins

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.

Nickel Chain-Walking Catalysis: A Journey to Migratory Carboboration of Alkenes

ConspectusChain-walking offers extensive opportunities for innovating synthetic methods that involve constructing chemical bonds at unconventional sites. This approach provides previously inaccessible retrosynthetic disconnections in organic synthesis. Through chain-walking, transition metal-catalyzed alkene difunctionalization reactions can take place in a 1,n-addition (n ≠ 2) mode. Unlike classical 1,2-regioselective difunctionalization reactions, there remains a scarcity of reports regarding migratory patterns. Moreover, the range of olefins utilized in these studies is quite limited.About five years ago, our research group embarked on a project aimed at developing valuable migratory difunctionalization reactions of alkenes through chain-walking. Our focus was on carboboration of alkenes utilizing nickel catalysis. The reaction commences with the migratory insertion of an olefin into a Ni-Bpin species. Subsequently, a thermodynamically stable alkyl nickel complex is generated through a chain-walking process. This complex then couples with a carbon-based electrophile, leading to the formation of an alkylboron compound. It is worth highlighting that the success of these transformations relies significantly on the utilization of a bisnitrogen-based ligand and LiOMe as a B2pin2 activator. Synthetically, these migratory carboboration reactions establish a robust platform for the rapid and efficient synthesis of a wide range of structurally diverse organoboron compounds, which are not facially accessed by conventional methods. The incorporation of a versatile boron group introduces a wealth of possibilities for subsequent diversifications, significantly enhancing the value of the resulting products and allowing for the creation of a broader range of valuable derivatives and applications.This Account provides a comprehensive overview of our research efforts and advancements in the field of migratory carboboration of unactivated alkenes using nickel catalysis. We begin by outlining the development of a series of 1,1-regioselective carboboration reactions of terminal alkenes. A significant focus is placed on the initial integration of boronate, which not only triggers the formation of thermodynamically stable metal species but also exerts control over remote stereochemistry in reactions involving substituted methylenecyclohexenes. Continuing our exploration, remarkable success is achieved in 1,3-regio- and cis-stereoselectivity when dealing with cyclic alkenes. Remarkably, nickel chain-walking catalysis enables heterocyclic alkenes to be viable coupling partners within our transformations. Moreover, it grants us the ability to achieve regioselectivity for cyclohexenes that was previously unattainable, thus expanding the horizons of regiochemical control in these reactions. Lastly, we present the evolution of ligand-modulated regiodivergent carboboration of allylarenes. By gaining insights into the underlying mechanisms driving regiodivergence, we lay a strong foundation for tackling challenges related to selecting specific sites in chain-walking reactions, especially when dealing with multiple stable factors. We anticipate that our findings, coupled with the mechanistic insights we've gained, will not only advance the realm of nickel chain-walking catalysis but also contribute to the broader understanding of selectivity control in reactions of this nature. This advancement will also catalyze the synthesis of intricate functional molecules, contributing to the creation of complex and valuable compounds in the realm of organic chemistry.

Mechanism and Origins of Regio- and Stereoselective Alkylboration of Endocyclic Olefins Enabled by Nickel Catalysis

The Ni-catalyzed alkylboration of endocyclic olefins is a stereo- and regioselective approach for the synthesis of boron-containing compounds. We report a detailed density functional theory (DFT) study to elucidate the mechanism and origins of the stereo-, chemo-, and regioselectivity of alkylboration of endocyclic olefins enabled by nickel catalysis. The alkylboration proceeds via the migratory insertion of alkenes, β-H elimination of the Ni(II) complex, subsequent migratory insertion leading to a new Ni(II) complex, combined with an alkyl radical, and reductive eliminations. The electronic effects of the endocyclic olefins synergistically control the regioselectivity toward the C1- and C2-position boration. In C1-position boration, a more electron-deficient carbon atom tends to combine with an electron-rich -Bpin group and leads to C1-position boration products. The stereoselectivity is influenced by the solvent effect, and the interaction between the substrate and Ni-catalyzed groups, the low-polarity solvent 1,4-dioxane, and a favorable steric hindrance effect result in the cis-alkylboration product. Chemoselectivity toward 1,3-alkylboration results from the steric hindrance effects of the -Bpin group.

Nickel-Catalyzed Reductive [4 + 1] Sila-Cycloaddition of 1,3-Dienes with Dichlorosilanes

Transition-metal-catalyzed sila-cycloaddition has been a promising tool for accessing silacarbocycle derivatives, but the approach has been limited to a selection of well-defined sila-synthons. Herein, we demonstrate the potential of chlorosilanes, which are industrial feedstock chemicals, for this type of reaction under reductive nickel catalysis. This work extends the scope of reductive coupling from carbocycle to silacarbocycle synthesis and from single C-Si bond formation to sila-cycloaddition reactions. The reaction proceeds under mild conditions and shows good substrate scope and functionality tolerance, and it offers new access to silacyclopent-3-enes and spiro silacarbocycles. The optical properties of several spiro dithienosiloles as well as structural variations of the products are demonstrated.

Ligand-controlled regiodivergence in cobalt-catalyzed hydrosilylation of isoprene

An atom-economical, regiodivergent hydrosilylation reaction of isoprene was developed using an Earth-abundant cobalt catalyst through variation of ligands.

Recent progress in nickel-catalyzed carboboration of alkenes

Alkenes represent one of the most useful building blocks for organic synthesis, owing to their abundance and versatile reactivity. Transition metal (Pd, Cu, Co, Ni, Fe, etc.) catalyzed difunctionalization of alkenes provides efficient access to substituted molecules from readily available alkenes by installing functional groups across their carbon-carbon double bonds. Particularly, Nickel-based catalytic complexes have attracted a great deal of attention. This is because they are prone to undergoing oxidative addition and slow β-hydride elimination, and can access both two-electron and radical pathways. Numerous elegant Ni-catalyzed cross-coupling methods, e.g., (hetero)arylboration, alkenylboration, alkylboration and alkynylboration of alkenes, have been developed with broad scopes and a high tolerance to a variety of functional groups. Therefore, the Ni-catalyzed carboboration of alkenes has become an efficient synthetic protocol to deliver substituted compounds by the cross-coupling of alkenes, electrophiles, and B₂Pin₂. Despite this progress, a number of challenging issues remaining in the field include broadening the types of carboboration reactions, especially the asymmetric ones, diversifying electrophile types (which is limited to halogens for now) and gaining profound insight into the reaction mechanisms. This review summarizes the recent progress in this emerging field from the literature published since 2018. It will provide the scientific community with convenience to access collective information and to accelerate their further research in order to broaden the scope of methodology and application in drug discovery programs.

Regioselective Ni-Catalyzed reductive alkylsilylation of acrylonitrile with unactivated alkyl bromides and chlorosilanes

Transition-metal catalyzed carbosilylation of alkenes using carbon electrophiles and silylmetal (-B, -Zn) reagents as the nucleophiles offers a powerful strategy for synthesizing organosilicones, by incorporating carbon and silyl groups across on C-C double bonds in one step. However, to the best of our knowledge, the study of silylative alkenes difunctionalization based on carbon and silyl electrophiles remains underdeveloped. Herein, we present an example of silylative alkylation of activated olefins with unactivated alkyl bromides and chlorosilanes as electrophiles under nickel catalysis. The main feature of this protocol is employing more easily accessible substrates including primary, secondary and tertiary alkyl bromides, as well as various chlorosilanes without using pre-generated organometallics. A wide range of alkylsilanes with diverse structures can be efficiently assembled in a single step, highlighting the good functionality tolerance of this approach. Furthermore, successful functionalization of bioactive molecules and synthetic applications using this method demonstrate its practicability.

Intermolecular Carbosilylation of α-Olefins with C(sp3 )-C(sp) Bond Formation Involving Silylium-Ion Regeneration

A regioselective addition of alkynylsilanes across unactivated, terminal alkenes is reported. The reaction is initiated by the capture of a sterically unhindered silylium ion by a silylated phenylacetylene derivative to form a bis(silylated) ketene‐like carbocation. This in situ‐generated key intermediate is the actual catalyst that maintains the catalytic cycle by a series of electrophilic addition reactions of silylium ions and β‐silicon‐stabilized carbocations. The computed reaction mechanism is fully consistent with the experimental findings. This unprecedented two‐component carbosilylation establishes a C(sp³)−C(sp) bond and a C(sp³)−Si bond in atom‐economic fashion.

Nickel/Brønsted acid dual-catalyzed regio- and enantioselective hydrophosphinylation of 1,3-dienes: access to chiral allylic phosphine oxides

While chiral allylic organophosphorus compounds are widely utilized in asymmetric catalysis and for accessing bioactive molecules, their synthetic methods are still very limited. We report the development of asymmetric nickel/Brønsted acid dual-catalyzed hydrophosphinylation of 1,3-dienes with phosphine oxides. This reaction is characterized by an inexpensive chiral catalyst, broad substrate scope, and high regio- and enantioselectivity. This study allows the construction of chiral allylic phosphine oxides in a highly economic and efficient manner. Preliminary mechanistic investigations suggest that the 1,3-diene insertion into the chiral Ni-H species is a highly regioselective process and the formation of the chiral C-P bond is an irreversible step.

Nickel-Catalyzed Reductive Cross-Coupling of Alkyl Bromides and Chlorosilanes

A novel nickel-catalyzed highly selective reductive cross-coupling of alkyl bromides and chlorosilanes to construct the C-Si bond has been developed. Under benign reaction conditions, a series of structurally interesting organosilanes can be accessed without Ni-catalyzed isomerization. The utility of this chemistry is illustrated by further transformations of the product. Moreover, the radical mechanism of the reaction is illustrated by control experiments.

Three-Component Ni-Catalyzed Silylacylation of Alkenes

A Ni-catalyzed silylacylation of alkenes is presented. The reaction combines alkenes, ClZnSiR₃, and acid chlorides to provide rapid access to β-silyl ketones. Importantly, the method involves a [Ni]-SiR₃ complex as a catalytic intermediate, which is rarely described for three-component alkene functionalization. Finally, the synthetic utility of the products is demonstrated, and the mechanistic details are described.