Palladium‐Catalyzed Oxidative C?H Bond Acylation of Acetanilides with Benzylic Alcohols

An efficient and clean method to construct C C bonds has been developed via the acylation reaction of acetanilides with benzylic alcohols using tert‐butyl hydroperoxide (TBHP) as oxidant catalyzed by palladium acetate in the presence of triflic acid (TfOH). The acylation reactions exhibit excellent reactivities, and up to 95% yield of the corresponding aryl ketone could be obtained under the optimal conditions.     

Ruthenium(II)‐Catalyzed Oxidative Annulation Reactions of Arylimidazolium Salts via N‐Heterocyclic Carbene‐Directed C?H Activation

An efficient ruthenium(II)‐catalyzed oxidative annulation reaction of various arylimidazolium salts with alkynes via N‐heterocyclic carbene‐directed C H activation to obtain substituted benzo[ij]imidazo[2,1,5‐de]quinolizinium salts is reported. This catalytic reaction proceeds in an excellent regioselective manner when using unsymmetrical alkynes as reactants. The intermediate mono‐annulated products can be obtained by reducing the amount of catalyst. Two catalytically competent N‐heterocyclic carbene‐based cyclometallated ruthenium(II) complexes have been isolated and characterized, which represent the key intermediates in the catalytic cycle. Moreover, most of the products show a strong fluorescent property, indicating their potential for making new light‐emitting materials.

     

Palladium‐Catalyzed C?N Cross‐Coupling of N′‐Monosubstituted Sulfondiimines with Aryl Bromides

A general method for the N‐arylation of sulfondiimines with aryl bromides using tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] and 2‐dicyclohexylphosphino‐2′,6′‐diisopropoxybiphenyl (RuPhos) as catalyst system was developed. A new benzothiazine was obtained, and a protocol for the cleavage of para‐methoxyphenyl (PMP) groups in PMP‐protected sulfondiimines has been found, which provides access to synthetically useful NH‐derivatives, that are difficult to prepare by other means.     

Nickel‐Catalyzed α‐Benzylation of Arylacetonitriles via C?O Activation

Efficient Ni‐catalyzed direct cross‐couplings of benzylic alcohol derivatives with arylacetonitriles via C O activation are described. Various α‐benzylated arylacetonitriles including those with functional groups can be prepared under mild reaction conditions.

     

Acylperoxycoumarins as ortho‐C?H Acylating Agent via a Palladium(II)‐Catalyzed Redox‐Neutral Process

An unprecedented palladium(II)‐catalyzed biomimetic aliphatic acyl (‐COR) group transfer was observed from acyl‐α‐peroxycoumarins to the ortho C H sites of directing arenes. Here, the C H activation is associated with a concomitant acyl group transfer via a Pd(II)‐catalyzed, redox‐neutral process. While methods for ortho aroylation (‐COAr) are well documented ortho acylation (‐COR) processes are scarce, hence the present redox‐neutral method is most ideal for o‐acylation of directing substrates.

     

Palladium‐Catalyzed Selective C?H Benzylation towards Functionalized Azoles with a Quaternary Carbon Center

The direct C H benzylation of azoles with benzyl chlorides proceeds efficiently, via sequential cleavage of one sp² C H bond and two sp³ C H bonds in the presence of a palladium catalyst, to generate a wide range of tribenzylated azoles with a quaternary carbon center efficiently. The same catalyst could also promote the mono‐ and di‐benzylation reactions through fine turning of the base and reaction conditions.     

Palladium‐Catalyzed Oxidative sp2 C?H Bond Acylation with Aldehydes

An efficient method was developed for the direct acylation of arene sp² C H bonds with aldehydes using palladium acetate as catalyst and peroxide as oxidant. The solvent‐free oxidative acylation reaction assisted by a pyridine directing group provides an easy access to aromatic, aliphatic, and optical active ketones.     

Rhodium(III)‐Catalyzed Direct C?H Olefination of Arenes with Aliphatic Olefins

A rhodium(III)‐catalyzed direct ortho C H bond olefination of arenes, including but not limited to benzamides, arylpyridines and indoles, with a variety of unactivated aliphatic olefins has been developed. In the presence of catalytic amounts of dichloro(pentamethylcyclopentadienyl)rhodium(III) dimer {[Cp*RhCl₂]₂}, copper(II) acetate monohydrate [Cu(OAc)₂⋅H₂O] and silver hexafluoroantimonate(V) (AgSbF₆), the coupling reaction occurred efficiently to afford the ortho‐olefinated linear products in good to excellent yields with high regio‐ and stereoselectivities, and a range of functional groups in both coupling partners is compatible with the reaction conditions. This protocol relies on the use of directing groups, and the addition of AgSbF₆ as additive is crucial for the catalysis. This new method expands the scope of rhodium(III)‐catalyzed direct C H bond olefination of arenes, and provides a rapid access to useful linear arylation products of unactivated olefins.

     

Mild Palladium‐Catalyzed Oxidative Direct ortho‐C?H Acylation of Anilides under Aqueous Conditions

Palladium‐catalyzed cross‐dehydrogenative coupling between anilides and aromatic aldehydes was achieved under aqueous conditions. A wide variety of the desired benzophenone derivatives was isolated in good to excellent yield. The reaction rate acceleration effect of acid and detergent has been demonstrated. Mechanistic insight has been obtained from quantum chemical calculations.     

Polyheterocycles by Palladium(II)‐Catalyzed Oxidative Domino Reactions Involving Direct C?H Functionalization

A novel palladium(II)‐catalyzed oxidative domino reaction sequence of diyne‐enones and substituted indoles to afford polyheterocycles involving direct C H functionalization using air as oxidant has been developed.     

Palladium‐Catalysed Dehydrogenative sp3 C?H Bonds Functionalisation into Alkenes: A Direct Access to N‐Alkenylbenzenesulfonamides

The palladium‐catalysed dehydrogenation of sp³ carbon‐hydrogen bonds of N‐alkylbenzenesulfonamides allows a simple access to N‐alkenylbenzenesulfonamides. The reaction proceeds with easily accessible catalysts, with pivalate as a base, and allows a variety of substituents both on nitrogen and on the arene moiety.

     

Iridium‐Catalyzed Annulation of Aromatic Imines with 1,3‐Dienes via Direct Functionalization of an Aromatic C?H Bond

The [3+2] annulation of N‐sulfonyl aromatic imines with 1,3‐dienes proceeded via a direct C H functionalization to give 1‐aminoindane derivatives in high yields with high regio‐ and stereoselectivities. The iridium complex coordinated with a substrate 1,3‐diene displayed high catalytic activity. The reaction proceeds via the direct formation of the aryliridium(I) species from the aromatic aldimine and an iridium(I) acetate species via a concerted metalation‐deprotonation pathway.

     

Mechanistic Switch via Subtle Ligand Modulation: Palladium‐Catalyzed Synthesis of α,β‐Substituted Styrenes via C?H Bond Functionalization

A new catalyst system able to efficiently perform the synthesis of styrenes via C H bond functionalization and a subtle ligand modification are described. The high level of activity achieved allows for the synthesis of highly functionalized α,β‐substituted styrenes, even the elusive E‐configured trisubstituted olefins, in a regio‐ and stereoselective manner. Mechanistic experiments allowed for the identification of the corresponding synthetic intermediates.     

C?C Bond Formation via C?H Activation and C?N Bond Formation via Oxidative Amination Catalyzed by Palladium‐ Polyoxometalate Nanomaterials Using Dioxygen as the Terminal Oxidant

An efficient heterogeneous palladium‐polyoxometalate catalyst with the formula Pd‐H₆PV₃Mo₉O₄₀/C has been successfully developed for carbon‐carbon (C C) bond formation via carbon‐hydrogen (C H) activation and carbon‐nitrogen (C N) bond formation via oxidative amination using oxygen as the terminal oxidant. The coupling processes are simple, and use relatively mild conditions to form the desired products. In addition, less waste is generated as no additional reagents such as organic/inorganic oxidants are required, and water is the only by‐product generated.     

Copper(II)‐Catalyzed Aerobic Oxidative Coupling between Chalcone and 2‐Aminopyridine via C?H Amination: An Expedient Synthesis of 3‐Aroylimidazo[1,2‐a]pyridines

A simple and efficient protocol has been developed for the synthesis of 3‐aroylimidazopyridines via copper(II) acetate‐catalyzed aerobic oxidative amination. A library of 3‐aroylimidazopyridines was synthesized from readily accessible chalcones and 2‐aminopyridines with high yields and regioselectivity. The reaction proceeds through a tandem Michael addition followed by an intramolecular oxidative amination. The successful application of this methodology for a gram‐scale reaction indicates its potential for bulk synthesis.

     

Iridium(III)‐Catalyzed Direct C?H Sulfonamidation of 2‐Aryl‐1,2,3‐triazole N‐Oxides with Sulfonyl Azides

We have developed a method for the direct sulfonamidation of 2‐aryl‐1,2,3‐triazole N‐oxides using sulfonyl azides as the amino source to release molecular nitrogen as the sole by‐product. This protocol exhibits excellent functional group tolerance and proceeds efficiently under external oxidant‐free conditions. Various 2‐(2‐sulfonamidoaryl)‐1,2,3‐triazoles were prepared in up to 97% yields for 25 examples with excellent regioselectivity.

     

Dearomatization of Indole Derivatives via Palladium‐Catalyzed C?H Bond Functionalization of Pyrroles: Convenient Construction of Spiroindolenines

An intramolecular palladium(II)‐catalyzed dearomative arylation reaction of indoles via C H bond functionalization was developed, providing access to structurally novel spiroindolenines with moderate to good yields. A one‐pot process for the synthesis of spiroindoline derivatives was also realized.

     

Palladium‐Catalyzed/Lewis Acid‐Promoted Alkene Dimerization and Cross‐Coupling with Alcohols via C?H Bond Activation

The cross‐couplings of alcohols to alkenes with the palladium/Lewis acid system are reported. This reaction occurs in a successive alkene dimerization, direct C H activation of alcohol and sp³ sp³ bond forming sequence via an interesting domino process.     

Palladium‐Catalyzed C?H Bond Acetoxylation: An Approach to ortho‐Substituted Hydroxy[2.2]paracyclophane Derivatives

The palladium‐catalyzed direct C H bond acetoxylation of [2.2]paracyclophanes has been investigated. Various mono‐ and disubstituted [2.2]paracyclophanes were subjected to typical Sanford acetoxylation conditions. Oxime ethers, an oxime acetate, a pyridine, and a pyrazole with [2.2]paracyclophane cores underwent direct ortho‐acetoxylation in good to excellent yields using 1–5 mol% of palladium(II) acetate in combination with iodobenzene diacetate as oxidant. The reactions could be performed on a multigram scale, and the ortho‐acetoxylated [2.2]paracyclophanes were suitable for further functionalizations affording a hydroxy[2.2]paracyclophane derivative and a planar chiral benzoxazole.     

Palladium‐Catalyzed C?H Functionalization of Ferrocenecarboxylic Acid by using 8‐Aminoquinoline as a Removable Directing Group

A mild and efficient palladium‐catalyzed synthetic method for the C H functionalization of N‐(quinolin‐8‐yl)ferrocenecarboxamide has been developed. Various aryl iodides containing I, NO₂, CN, COMe, CO₂Et, and NH functionalities and also alkyl iodides underwent the Pd‐catalyzed intermolecular carbon‐carbon bond forming reaction with ferrocenecarboxamide successfully which led to a diverse array of bis(aryl/alkyl)ferrocenecarboxamides in 34–92% yields. Cross‐coupling of the ferrocenyl C H bond with aryl iodides can also be achieved utilizing an economical Ni catalyst. Additionally, selective monoalkylation of ferrocenecarboxamide was studied using sodium bicarbonate as base and dibenzylphosphoric acid as additive under Pd‐catalyzed reaction conditions. Subsequently, removal of the directing group, 8‐aminoquinoline, from bis(aryl)ferrocenecarboxamides led to bis(aryl)ferrocenes bearing versatile methyl ester and carboxaldehyde functional groups.