NBE-Controlled Palladium-Catalyzed Interannular Selective C-H Silylation: Access to Divergent Silicon-Containing 1,1'-Biaryl-2-Acetamides

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.

Pd(0)-Catalyzed Intermolecular Methylene C(sp3)-H Silylation by Using N-Heterocyclic Carbene Ligands

The direct functionalization of methylene C(sp3)-H bonds is one of the greatest challenges in transition metal-catalyzed C-H activation. Although Pd(0)-catalyzed intramolecular cyclization reactions of methylene C(sp3)-H bonds have been reported, intermolecular functionalization remains to be discovered. Herein, we report the first example of a Pd(0)-catalyzed intermolecular methylene C(sp3)-H functionalization reaction. By use of a N-heterocyclic carbene ligand, the methylene C(sp3)-H bonds of 1-(benzyloxy)-2-iodobenzenes are activated and disilylated with hexamethyldisilane, affording disilylated products.

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.

Norbornene Derivatives-Controlled Palladium-Catalyzed Divergent Synthesis of Dibenzo[a,c]cycloheptenones and Fluorenones from Aryl Iodides and α-Oxocarboxylic Acids

A palladium-catalyzed divergent cascade decarboxylative annulation of aryl iodides and α-oxocarboxylic acids using norbornene (NBE) derivatives as a controlled switch is reported. When NBE is used as a mediator, fluorenones are synthesized with moderate to excellent yields via a Catellani reaction that involves sequential ortho-C-H arylation and ipso-decarboxylative acylation of aryl iodides. Employing oxanorbornadiene (ONBD) instead of NBE enables the assembly of dibenzo[a,c]cycloheptenones by a retro-Diels-Alder reaction rather than the release of an ONBD. Additionally, the synthetic utility of this method is demonstrated by the diversification of the products.

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.

Palladium-Catalyzed Multicomponent Assembly of (Z)-Alkenylborons via Carbopalladation/Boronation/Retro-Diels-Alder Cascade Reaction

A palladium-catalyzed multicomponent cascade reaction of aryl iodides, oxanorbornadiene, and diborns to access (Z)-alkenylborons is reported. This transformation proceeds through the sequential carbopalladation/boronation/retro-Diels-Alder domino reaction. The oxanorbornadiene used in this reaction serves as an acetylene surrogate, which is generated via a retro-Diels-Alder reaction. Such a stereoselective and scalable approach has a wide range of functional group tolerance and good substrate universality.

Palladium-catalyzed disilylation of ortho-halophenylethylenes enabled by 2-pyridone ligand

A palladium-catalyzed disilylation reaction applicable for a variety of non-, α-, or β-substituted and α,β-disubstituted ortho-halophenylethylenes has been developed. This reaction proceeds with high yields and very low catalyst loadings. The two C-Si bonds of the disilylated products could be well-differentiated chemoselectively in the reaction with various electrophiles.

Palladium-catalyzed cross-coupling of 2-iodobiphenyls with ortho-chloroacetophenones through dual C–H arylation for the construction of tribenzo[a,c,f]cyclooctanones

A Pd-catalyzed cross-coupling reaction of 2-iodobiphenyls with ortho-chloroacetophenones has been developed through C–H activation. The reaction provides a straightforward method for the construction of tribenzo[a,c,f]cyclooctanones.

Palladium-Catalyzed ortho-C(sp2)-H Silylation of Aromatic Ketones Using an Aminooxyamide Auxiliary

A palladium-catalyzed direct and selective ortho-C(sp²)-H silylation of aromatic ketones has been achieved using an aminooxyamide auxiliary. The reaction tolerates various orth-, meta-, and para- substituents on the aromatic ring and can be applied to thiophenyl and vinyl ketones. The ortho-C(sp²)-H bond was monosilylated selectively in comparison with other aromatic C-H bonds, benzyl or allylic C(sp³)-H bonds, and acidic α-C(sp³)-H bonds. The aminooxyamide auxiliary can be easily installed and readily removed after the silylation reaction. The resulting ortho-silyl aromatic ketone derivatives are potentially useful building blocks for organic synthesis.

Synthesis of 9-Fluorenylidenes via Pd-Catalyzed C-H Vinylation with Vinyl Bromides

A facile and efficient approach for the synthesis of 9-fluorenylidenes has been developed via the palladium-catalyzed cross-coupling of 2-iodobiphenyls and vinyl bromides. The reaction involves the C-H activation of 2-iodobiphenyls and dual C-C bond formations. A range of 9-fluorenylidene derivatives, including diphenyldibenzofulvenes, can be synthesized with the reaction.

Me3SiSiMe2(O n Bu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.

α-Bromoacrylic Acids as C1 Insertion Units for Palladium-Catalyzed Decarboxylative Synthesis of Diverse Dibenzofulvenes

Herein α-bromoacrylic acids have been employed as C1 insertion units to achieve the palladium-catalyzed [4 + 1] annulation of 2-iodobiphenyls, which provides an efficient platform for the construction of diverse dibenzofulvenes. This protocol enables the formation of double C(aryl)-C(vinyl) bonds via a C(vinyl)-Br bond cleavage and decarboxylation. It is particularly noteworthy that the method features a broad substrate scope, and various interesting frameworks, such as bridged ring, fused (hetero)aromatic ring, and divinylbenzene, can be successfully incorporated into the products.

Copper-Catalyzed Direct sp2 C-H Silylation of Arylamides Using Disilanes

A copper-catalyzed method for direct intermolecular ortho-silylation of benzamides has been developed that affords organosilane products in moderate to high yields. The key features include: (i) use of commercially available disilanes as a silicon source with 8-aminoquinoline as a bidentate directing group, (ii) use of earth-abundant first-row transition metal, (iii) operationally simple conditions without the need of an inert atmosphere, and (iv) tolerance of a wide range of functional groups. The practicality and effectiveness of this method have been demonstrated by a gram-scale experiment. This strategy, therefore, constitutes a convenient way of constructing C-Si bonds useful for synthetic organic chemistry.

An effective and versatile strategy for the synthesis of structurally diverse heteroarylsilanes via Ir(iii)-catalyzed C-H silylation

A versatile silylation of heteroaryl C–H bonds is accomplished under the catalysis of a well-defined spirocyclic NHC Ir(iii) complex (SNIr), generating a variety of heteroarylsilanes. A significant advantage of this catalytic system is that multiple types of intermolecular C–H silylation can be achieved using one catalytic system at α, β, γ, or δ positions of heteroatoms with excellent regioselectivities. Mechanistic experiments and DFT calculations indicate that the polycyclic ligand of SNIr can form an isolable cyclometalated intermediate, which leaves a phenyl dentate free and provides a hemi-open space for activating substrates. In general, favorable silylations occur at γ or δ positions of chelating heteroatoms, forming 5- or 6-membered C–Ir–N cyclic intermediates. If such an activation mode is prohibited sterically, silylations would take place at the α or β positions. The mechanistic studies would be helpful for further explaining the reactivity of the SNIr system.

A versatile silylation of heteroaryl C–H bonds is accomplished under the catalysis of a well-defined spirocyclic NHC Ir(iii) complex (SNIr), generating a variety of heteroarylsilanes.

Oxidation of Pd(II) with disilane in a palladium-catalyzed disilylation of aryl halides: a theoretical view

Density functional theory (DFT) calculation has been used to reveal the mechanism of the Pd-catalyzed disilylation reaction of aryl halides. The DFT calculations indicate that the reaction starts with the oxidative addition of the C-I bond to the Pd(0) catalyst. Concerted metalation-deprotonation (CMD) can then generate a five-membered palladacycle. Insertion of Pd(ii) into the Si-Si bond in disilane followed by two sequential steps of reductive eliminations yields the disilylation product and regenerates the Pd(0) catalyst. According to the NPA charge analysis along the reaction coordinates, the formal oxidative addition of the Si-Si bond to palladium could be considered as the insertion of palladium into the Si-Si bond. However, the conventional oxidative addition of the C-I bond to palladium is exactly an oxidation process with the electron transfer from the palladium atom to the C-I bond. Therefore, electron rich Pd(0) is beneficial for the oxidation process, and Pd(ii) prone to acquire electrons is beneficial for the insertion process.

Palladium-catalyzed domino Heck-disilylation and Heck-monosilylation of alkene-tethered carbamoyl chlorides: synthesis of versatile silylated oxindoles

We report efficient domino Heck-disilylation and Heck-monosilylation of alkene-tethered carbamoyl chlorides with hexamethyldisilane under mild reaction conditions.

A Catellani and retro-Diels–Alder strategy to access 1-amino phenanthrenes via ortho- and interannular C–H activation of 2-iodobiphenyls

A palladium-catalyzed three-component domino reaction for the construction of 1-amino phenanthrene derivatives by ortho- and interannular C–H activation of 2-iodobiphenyls has been developed.

A palladium-catalyzed Heck/[4 + 1] decarboxylative cyclization cascade to access diverse heteropolycycles by using α-bromoacrylic acids as C1 insertion units

A novel palladium-catalyzed Heck/[4 + 1] decarboxylative cyclization cascade of alkene-tethered aryl iodides by employing α-bromoacrylic acids as C1 insertion units is reported.

C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates

In this review article, we summarized recent advances in C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates.

Relay Palladium/Copper Catalysis Enabled Silylative [5 + 1] Benzannulation Using Terminal Alkynes as One-Carbon Units

Using terminal alkyne as a nontraditional one-carbon (C1) unit and silylborane as an external silicon pronucleophile, a relay palladium/copper-catalyzed silylative [5 + 1] benzannulation of 3-acetoxy-1,4-enynes for producing polysubstituted arylsilanes, especially including bioactive motif-based analogues, in a single reaction step through benzene ring skeleton assembly and silyl intermolecular incorporation cascades is developed. Mechanistic studies show that this reaction allows the terminal sp-hybridized carbon atom in terminal alkynes as a C1 unit via cleavage of two π-bonds and one C(sp)-H bond.

Palladium-catalyzed domino Heck-disilylation and -borylation of alkene-tethered 2-(2-halophenyl)-1H-indoles: access to diverse disilylated and borylated indolo[2,1-a]isoquinolines

A chemoselective domino Heck-disilylation and -borylation reaction for generating various disilylated and borylated tetracyclic indolo[2,1-a]isoquinolines has been developed.

Palladium-catalyzed intermolecular C–H silylation initiated by aminopalladation

The intermolecular disilylation reaction of C,C-palladacycles obtained through aminopalladation has been developed.

Pd-Catalyzed one-pot synthesis of vinylsilanes via a three-component tandem reaction

A palladium-catalyzed three-component tandem reaction for stereoselective assembly of various tri- or tetrasubstituted vinylsilanes is established.

A denitrogenative palladium-catalyzed cascade for regioselective synthesis of fluorenes

We herein report a denitrogenative palladium-catalyzed cascade for the modular and regioselective synthesis of polysubstituted fluorenes. Hydrazone facilitates the Pd(ii) to Pd(iv) oxidative addition in a Catellani pathway and is also the methylene synthon in the proposed reaction. Aryl iodides and 2-bromoarylaldehyde hydrazones undergo a norbornene-controlled tandem reaction sequence to give a broad scope of fluorenes in the presence of a palladium catalyst. The method described is scalable and adaptable to a three-component reaction with in situ generation of the hydrazone group. Preliminary mechanistic investigations have been conducted.