Palladium-Catalyzed Reaction of o-Alkynyltrifluoroacetanilides with 1-Bromoalkynes. An Approach to 2-Substituted 3-Alkynylindoles and 2-Substituted 3-Acylindoles

Palladium-catalyzed synthesis of 2,3-disubstituted indoles via arylation of ortho-alkynylanilines with arylsiloxanes

In this study, we report the electrophilic cyclization of N,N-dimethyl-o-alkynylanilines with arylsiloxanes in the presence of [Pd(OAc)2] and Ag2O catalytic system, which leads to the efficient synthesis of indoles, similar to the one that is obtained through Larock indole synthesis. A range of aryl(trimethoxy)silanes with EDGs and EWGs were successfully utilized for the synthesis of a diverse variety of substituted indoles via the cleavage of the C-Si bond. This protocol exhibits good functional group tolerance and wide substrate scope to provide 2,3-diaryl-N-methylindoles in 26-88% yields.

Arylation and Aryne Insertion into C-Acylimines: A Simple, Flexible, and Divergent Synthesis of C2-Aryl Indoles

We reveal a direct strategy for the flexible synthesis of C2-aryl/heteroaryl indoles without transition metal catalysts. The synthesis involves a one-pot, four-component reaction of readily available starting materials to offer diversity around the indole moiety with a broad substrate scope and high yields. The reaction proceeds via the Friedel-Crafts C-arylation of C-acylimine formed in situ, followed by N-arylation with aryne, a formal [3+2] cycloaddition, and a subsequent aromatization cascade.

1,2-Aminofunctionalization Reactions of Pyridino-Alkynes via Carbophilic Activation

Transition metal-catalyzed 1,2-difunctionalization reactions of alkynes have emerged as a powerful tool to forge carbon-carbon and carbon-heteroatom bonds for the rapid synthesis of polyfunctionalized molecular scaffolds. In this regard, our group has persistently been developing transition metal-mediated 1,2-aminofunctionalization reactions of alkynes through a rationally designed pyridino-alkyne core by utilizing the carbophilic activation strategy. In this account, we present an array of such 1,2-aminofunctionalization reactions which have been successfully executed on this core to afford important polycyclic frameworks such as functionalized quinalizinones, pyridinium oxazole dyads (PODs), N-doped polycyclic aromatic hydrocarbons (PAHs), N-doped spiro-PAHs. Additionally, the synthesis of phosphine ligated gold complexes bearing pyrido-isoquinoline scaffold from the pyridino-alkynes will be discussed briefly.

Palladium-catalyzed regio- and stereoselective synthesis of aryl and 3-indolyl-substituted 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones

Cascade cyclocarbopalladation of the readily available aryl/alkyl-substituted propargylic amides containing an aryl iodide moiety, followed by Suzuki–Miyaura coupling with arylboronic acids, allowed an efficient regio- and stereoselective synthesis of tetrasubstituted 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones. Moreover, cascade cyclocarbopalladation, followed by the reaction with 2-alkynyltrifluoroacetanilides, accomplished a double cyclization to afford challenging 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones bearing a 3-indolyl substituent through aminopalladation/reductive elimination.

Lewis Acid Catalyzed Atom-Economic Synthesis of C2-Substituted Indoles from o-Amido Alkynols

Herein we have disclosed a Zn(OTf)₂ catalyzed synthesis of C2-alkyl substituted indole derivatives via unprecedented carbonyl group migration from o-amido alkynols. The key features of this protocol involve N,O-carbonyl group migration, broad substrate scope with varied functionality tolerance, moderate to good yields, and 100% atom economy. The crossover experiments proved that the migration is happening via an intramolecular pathway.

Transition Metal-Catalyzed Reactions of Alkynyl Halides

BACKGROUND

Transition metal-catalyzed reactions of alkynyl halides are a versatile means of synthesizing a wide array of products. Their use is of particular interest in cycloaddition reactions and in constructing new carbon-carbon and carbon-heteroatom bonds. Transition metal-catalyzed reactions of alkynyl halides have successfully been used in [4+2], [2+2], [2+2+2] and [3+2] cycloaddition reactions. Many carbon-carbon coupling reactions take advantage of metal-catalyzed reactions of alkynyl halides, including Cadiot-Chodkiewicz, Suzuki-Miyaura, Stille, Kumada-Corriu and Inverse Sonogashira reactions. All the methods of constructing carbon-nitrogen, carbon-oxygen, carbon-phosphorus, carbon-sulfur, carbon-silicon, carbon-selenium and carbon-tellurium bonds employed alkynyl halides.

OBJECTIVE

The purpose of this review is to highlight and summarize research conducted in transition metalcatalyzed reactions of alkynyl halides in recent years. The focus will be placed on cycloaddition and coupling reactions, and their scope and applicability to the synthesis of biologically important and industrially relevant compounds will be discussed.

CONCLUSION

It can be seen from the review that the work done on this topic has employed the use of many different transition metal catalysts to perform various cycloadditions, cyclizations, and couplings using alkynyl halides. The reactions involving alkynyl halides were efficient in generating both carbon-carbon and carbonheteroatom bonds. Proposed mechanisms were included to support the understanding of such reactions. Many of these reactions face retention of the halide moiety, allowing additional functionalization of the products, with some new products being inaccessible using their standard alkyne counterparts.

Palladium-catalyzed C-glycosylation and annulation of o-alkynylanilines with 1-iodoglycals: convenient access to 3-indolyl-C-glycosides

An efficient and practical approach for the synthesis of 3-indolyl-C-Δ1,2-glycosides through a palladium-catalyzed annulation/C-glycosylation sequence of o-alkynylanilines with 1-iodoglycals has been developed. This methodology has a wide scope of substrates and gives access to 3-indolyl-C-Δ1,2-glycosides in high yields. Furthermore, the product obtained here exhibits a high utility for further transformations.

Palladium-catalyzed regioselective C–H alkynylation of indoles with bromoalkynes in water

A palladium-catalyzed regioselective C(sp²)–H alkynylation between indoles and bromoalkynes in water has been developed, affording diverse functionalized 2-alkynylindoles in good yields.

Copper-Catalyzed Synthesis of Substituted Quinazolines from Benzonitriles and 2-Ethynylanilines via Carbon-Carbon Bond Cleavage Using Molecular Oxygen

A copper-catalyzed process for the synthesis of substituted quinazolines from benzonitriles and 2-ethynylanilines using molecular oxygen (O₂) as sole oxidant is described. The mild catalytic system enabled the effective cleavage of the C-C triple bond and construction of new C-N and C-C bonds in one operation. Furthermore, the compound N, N-dimethyl-4-(2-(4-(trifluoromethyl)phenyl)quinazolin-4-yl)aniline (3dj) exhibited obvious aggregation-induced emission phenomenon, and the fluorescence quantum yield (Φ_F,film) and lifetime (τ_film) were measured to be 45.5% and 5.8 ns in thin films state, respectively.

N-Heterocyclic carbene palladium-catalyzed cascade annulation/alkynylation of 2-alkynylanilines with terminal alkynes

A straightforward and highly effective N-heterocyclic carbene-palladium catalyzed cascade annulation/alkynylation of 2-alkynylanilines with terminal alkynes has been enabled to afford free (NH)-3-alkynylindole derivatives in moderate to good yields. This protocol features mild conditions, broad substrate scope, and high atom- and step-economy. Notably, the resultant 3-alkynylindoles could be conveniently transformed into a variety of functionalized indole scaffolds, thus illustrating their potential applications in synthetic and pharmaceutical chemistry.

Gold-catalyzed domino cyclization–alkynylation reactions with EBX reagents: new insights into the reaction mechanism

New insights into the mechanism of gold-catalyzed domino reactions with hypervalent iodine reagents revealed by computation and confirmed by experiments.

Efficient access to alkynylated quinalizinones via the gold(i)-catalyzed aminoalkynylation of alkynes

The gold-catalyzed aminoalkynylation of alkynes for the synthesis of quinalizinones from pyridinoalkynes using 1-[(triisopropylsilyl)-ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) is reported.

Synthesis of 3-bromosubstituted pyrroles via palladium-catalyzed intermolecular oxidative cyclization of bromoalkynes with N-allylamines

A novel Pd-catalyzed intermolecular oxidative cyclization of bromoalkynes with N-allylamines to construct 3-bromo-pyrrole derivatives has been developed.

“Quick and click” assembly of functionalised indole rings via metal-promoted cyclative tandem reactions

An efficient and convenient synthesis of a variety of decorated indoles using a three-component tandem metal-catalysed process is described.