Palladium-catalyzed oxidative allylic C-H silylation

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.

Palladium-Catalyzed Organic Reactions Involving Hypervalent Iodine Reagents

The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C—H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C—H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.

Metal-catalyzed silylation of sp3C–H bonds

Metal-catalyzed activations of inert sp³C–H bonds have recently brought a revolution in the synthesis of useful molecules and molecular materials, due to the interest of the formed sp³C–SiR₃ silanes, stable organometallic species, and for further functionalizations that sp³C–H bonds cannot reach directly.

Hypervalent Iodine Reagents in Palladium-Catalyzed Oxidative Cross-Coupling Reactions

Hypervalent iodine compounds are valuable and versatile reagents in synthetic organic chemistry, generating a diverse array of useful organic molecules. Owing to their non-toxic and environmentally friendly features, these reagents find potential applications in various oxidative functionalization reactions. In recent years, the use of hypervalent iodine reagents in palladium-catalyzed transformations has been widely studied as they are strong electrophiles and powerful oxidizing agents. For instance, extensive work has been carried out in the field of C–H bond functionalization via Pd-catalysis using hypervalent iodine reagents as oxidants. In addition, nowadays, iodine(III) reagents have been frequently employed as arylating agents in Pd-catalyzed C–H arylation or Heck-type cross-coupling reactions. In this review, recent advancements in the area of palladium-catalyzed oxidative cross-coupling reactions using hypervalent iodine reagents are summarized in detail.

Redox-Neutral Propargylic C–H Functionalization by Using Iron Catalysis

In spite of their rich stoichiometric chemistry, cyclopentadienyliron(II) dicarbonyl complexes are rarely used as catalysts in organic synthesis. Inspired by precedents in the chemistry of cationic olefin complexes and neutral allylmetal species, our group has developed a coupling of alkynes or alkenes with aldehydes and other carbonyl electrophiles to give homopropargylic and homoallylic alcohols, respectively, by using a substituted cyclopentadienyliron(II) dicarbonyl complex as the catalyst. In this article, we first contextualize this development within the conceptual background of C–H functionalization chemistry and relative to key stoichiometric precedents. We then give an account of our group’s discovery and development of the catalytic α-functionalization of alkenes and alkynes with electrophilic reagents.

Introduction

Preliminary Stoichiometric Work

Hydroxyalkylation Development and Scope

Conclusions and Future Directions

Allylation of β-amino phosphonic acid precursor via palladium-NHC catalyzed allylic C–H activation

A Pd(ii)/N-heterocyclic carbene (NHC) catalyzed allylic C–H alkylation of allylbenzene with α-cyano-phosphate ester has been achieved under mild reaction conditions with the highest regioselectivity and stereoselectivity.

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

A novel palladium-catalyzed interannular selective C-H silylation of 1,1'-biaryl-2-acetamides is described. The combination of palladium catalyst with copper oxidant enables meta- or ortho-selective C-H silylation by employing hexamethyldisilane as a trimethylsilyl source, which relies on the control of NBE derivatives as a switch, thus providing straightforward access to divergent silicon-containing 1,1'-biaryl-2-acetamides.

Palladium-catalyzed allylic C-H oxidation under simple operation and mild conditions

We discovered an effective and simple system (Pd/BQ/air/r.t.) for making allylic alcohols through Pd-catalyzed allylic C-H bond functionalization. This approach exhibits advantages due to its simple operation, mild conditions, and environmentally benign features. By modifying reaction conditions, it can be suitable for preparing unsaturated aldehydes, allylic esters, ethers, and amines.

Palladium-catalyzed oxidative allylation of bis[(pinacolato)boryl]methane: synthesis of homoallylic boronic esters

A novel palladium-catalyzed approach for constructing homoallylic boronic esters via oxidative allylic C–H functionalization of allylic hydrocarbons has been demonstrated.

Palladium-Catalyzed Oxidative Borylation of Allylic C-H Bonds in Alkenes

This communication describes an efficient palladium pincer complex-catalyzed allylic C-H borylation of alkenes. The transformation exhibits high regio- and stereoselectivity with a variety of linear alkenes. A synthetically useful feature of this allylic C-H borylation method is that all allyl-Bpin products can be isolated in usually high yields. Preliminary mechanistic studies indicate that this C-H borylation reaction proceeds via Pd(IV) pincer complex intermediates.

Experimental and Computational Exploration of para-Selective Silylation with a Hydrogen-Bonded Template

The regioselective conversion of C-H bonds into C-Si bonds is extremely important owing to the natural abundance and non-toxicity of silicon. Classical silylation reactions often suffer from poor functional group compatibility, low atom economy, and insufficient regioselectivity. Herein, we disclose a template-assisted method for the regioselective para silylation of toluene derivatives. A new template was designed, and the origin of selectivity was analyzed experimentally and computationally. An interesting substrate-solvent hydrogen-bonding interaction was observed. Kinetic, spectroscopic, and computational studies shed light on the reaction mechanism. The synthetic significance of this strategy was highlighted by the generation of a precursor of a potential lipophilic bioisostere of γ-aminobutyric acid (GABA), various late-stage diversifications, and by mimicking enzymatic transformations.

Palladium-Catalyzed Aerobic Oxygenation of Allylarenes

An efficient and practical protocol for the synthesis of (E)-allylethers from readily available olefins with alcohols or phenols was developed. This aerobic oxidative allylic C-H oxygenation protocol features mild conditions, broad substrate scope, and high atom and step economy, making it a valuable and convenient synthetic method. Notably, molecular oxygen is the sole oxidant in this novel transformation.

Iridium-catalyzed intermolecular directed dehydrogenative ortho C–H silylation

An efficient method for iridium-catalyzed direct silylation of C(sp²)–H and C(sp³)–H bonds using HSiMe(OSiMe₃)₂ as the silylating reagent is described.

Palladium-Catalyzed Allylic C-H Oxidative Annulation for Assembly of Functionalized 2-Substituted Quinoline Derivatives

An efficient and practical palladium-catalyzed aerobic oxidative approach to afford functionalized 2-substituted quinolines in moderate to good yields from readily available allylbenzenes with aniline is developed. The present annulation process has high functional-group tolerance and high atom economy, making it a valuable and practical method in synthetic and medicinal chemistry. Moreover, this transformation is supposed to proceed through oxidation of allylic C-H functionalization to form C-C and C-N bonds in one pot.

Ruthenium-Catalyzed Intermolecular Direct Silylation of Unreactive C(sp(3))-H Bonds

A Ru-catalyzed intermolecular silylation of unreactive, aliphatic C(sp(3))-H bonds has been described for the first time. This protocol features low catalyst loading, a relatively broad substrate spectrum, good functional group tolerance, and no sensitivity to air, which provides a convenient and practical pathway for the construction of C-Si bonds.

Ru-catalysed C–H silylation of unprotected gramines, tryptamines and their congeners

Directed and undirected Ru-catalysed C–H silylation of unprotected heteroarenes is presented which requires no protecting groups.

Palladium-catalyzed aerobic oxidative double allylic C–H oxygenation of alkenes: a novel and straightforward route to α,β-unsaturated esters

We reported a strategically distinct approach to synthesize α,β-unsaturated esters through palladium-catalyzed aerobic oxidative double allylic C–H oxygenation of alkenes.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Palladium-catalyzed regioselective azidation of allylic C–H bonds under atmospheric pressure of dioxygen

A palladium-catalyzed allylic azidation of alkenes with sodium azide under atmospheric pressure of dioxygen was developed.

Palladium-catalyzed aerobic oxidative allylic C–H arylation of alkenes with polyfluorobenzenes

Palladium-catalyzed aerobic oxidative direct allylic C–H arylation of alkenes, with polyfluorobenzenes, for the creation of allyl–aryl bonds, is reported.

Fused heteroaromatic dihydrosiloles: synthesis and double-fold modification

An efficient method for the synthesis of fused heteroaromatic dihydrosiloles via Ni-catalyzed hydrosilylation/intramolecular Ir-catalyzed dehydrogenative coupling of the Si-H bond with the heteroaromatic C-H bond has been developed. The method is efficient for both electron-deficient and -rich heterocycles. It exhibits high functional group tolerance and good regioselectivity. Fused heteroaromatic dihydrosiloles can be smoothly halogenated and then oxidized or arylated. Application of these transformations allows obtaining highly functionalized heteroaromatic structures. A gram-scale synthesis of dihydropyridinosilole has also been accomplished using reduced amounts of Ni- and Ir-catalysts.