B(C6F5)3-mediated direct intramolecular C7-alkenylation of N-propargylindoles

B(C6F5)3-mediated direct C7-alkenylation of N-propargylindoles without directing groups was developed. This reaction proceeds via the π-activation of the alkynyl group with B(C6F5)3/Friedel-Crafts alkenylation/proton transfer reaction sequence. Interestingly, C7-alkenylation products could further convert into the fused indoles by deprotonation and finally polyaromatic N-heterocycles by the hydride abstraction.

Pd-Catalyzed C-7 Arylation of Indolines with Aryltriazenes under Mild Conditions

A palladium-catalyzed direct C-H arylation of indolines at C-7 position has been achieved at near-ambient temperature. The reaction was carried out with aryltriazene as a stable aryl source and electron shuttle to sustainably release aryl radical in situ under the action of promoter, and pyrimidine as a detachable directing group for the synthesis of 7-arylindolines under oxidant- and ligand-free conditions. Notably, this catalytic system can also be applied to the direct and site-selective arylation of tetrahydroquinolines (C-8) and carbazoles (C-1).

Cobalt(III)-Catalyzed Directed C-7 Selective C-H Alkynylation of Indolines with Bromoalkynes

A cobalt(III)-catalyzed directed C-7 alkynylation of indolines with easily accessible bromoalkynes has been developed. The reaction has a broad substrate scope with excellent yields and represents a powerful route to the synthesis of 7-alkynyl-substituted indolines. In addition, the reaction can be extended to the coupling of N-aryl 7-azaindoles, highlighting the synthetic practicability of the strategy.

Direct Synthesis of Biphenyl-2-carbonitriles by Rh(III)-Catalyzed C-H Hiyama Cross-Coupling in Water

This method represents an efficient rhodium(III)-catalyzed o-C-H arylation of readily available benzimidate derivatives with diverse arylsilanes in water as a sustainable solvent, enabling the straightforward synthesis of potentially useful biphenyl-2-carbonitrile derivatives. This silicon-based protocol employs benzimidates as both an efficacious directing group and the source of a nitrile group.

Rhodium-catalysed decarbonylative C(sp2)-H alkylation of indolines with alkyl carboxylic acids and carboxylic anhydrides under redox-neutral conditions

We developed a rhodium-catalysed decarbonylative C(sp²)-H alkylation method for indolines. This reaction facilitates the use of alkyl carboxylic acids and their anhydrides as a cheap, abundant and non-toxic alkyl source under redox-neutral conditions, featuring the introduction of a primary alkyl chain, which cannot be addressed by previous radical-mediated decarboxylative reaction. Through a mechanistic investigation, we revealed that an initially formed C-7 acylated indoline was transformed into the corresponding alkylated indoline via a decarbonylation process.

Recent advances in rhodium-catalyzed C(sp2)-H (hetero)arylation

Arylation is a common behaviour in organic synthesis for the construction of complex structures, especially the biaryls. Among those reported arylation procedures, transition-metal-catalyzed direct C(sp²)-H arylation has been rapidly developed in recent decades and has become a reliable alternative to traditional cross-coupling procedures using organometallic reagents. Great achievements in rhodium-catalyzed C(sp²)-H arylation have been witnessed during the last decade. Aryl halides, simple arenes, aryl boronic acids, arylsilanes, aryl aldehyde, aryl carboxylic acid, diazides, etc. were successfully utilized as arylating reagents under rhodium-catalyzed conditions. In this review, recent achievements in rhodium-catalyzed arylations through C(sp²)-H bond activation were summarized together with the mechanism discussions.

Domino Heck/Hiyama cross-coupling: trapping of the σ-alkylpalladium intermediate with arylsilanes

A palladium-catalyzed domino Heck cyclization/Hiyama coupling reaction by the trapping of the σ-alkylpalladium intermediate with arylsilanes is described. A wide range of aryl-tethered alkenes and arylsilanes are all compatible with the reaction conditions. This approach shows good yields and excellent functional group tolerance, presenting a more practical and sustainable alternative to the conventional domino Heck cyclization/Suzuki coupling reaction.

Rhodium(III)-Catalyzed Direct C-H Arylation of Various Acyclic Enamides with Arylsilanes

The stereoselective β-C(sp²)-H arylation of various acyclic enamides with arylsilanes via Rh(III)-catalyzed cross-coupling reaction was illustrated. The methodology was characterized by extraordinary efficacy and stereoselectivity, a wide scope of substrates, good functional group tolerance, and the adoption of environmentally friendly arylsilanes. The utility of this present method was evidenced by the gram-scale synthesis and further elaboration of the product. In addition, Rh(III)-catalyzed C-H activation is considered to be the critical step in the reaction mechanism.

Pd-Catalyzed C-H Halogenation of Indolines and Tetrahydroquinolines with Removable Directing Group

Pd-catalyzed directing-group-assisted regioselective halogenations to C7 of indolines and C8 of tetrahydroquinolines were achieved in good to excellent yields. The practicality and utility of the developed method have been illustrated by various functional group transformations such as arylation, alkenylation, cyanation, and silylation utilizing the installed synthetic handle. The concise synthesis of primaquine, an antimalarial drug, and formal syntheses of two bioactive natural products, hippadine and pratosine, have also been demonstrated.

Steering Site-Selectivity in Transition Metal-Catalyzed C-H Bond Functionalization: the Challenge of Benzanilides

Selective C-H bond functionalization catalyzed by metal complexes have completely revolutionized the way in which chemical synthesis is conceived nowadays. Typically, the reactivity of a transition metal catalyst is the key to control the site-, regio- and/or stereo-selectivity of a C-H bond functionalization. Of particular interests are molecules that contain multiple C-H bonds prone to undergo C-H bond activations with very similar bond dissociation energies at different positions. This is the case of benzanilides, relevant chemical motifs that are found in many useful fine chemicals, in which two C-H sites are present in chemically different aromatic fragments. In the last years, it has been found that depending on the metal catalyst and the reaction conditions, the amide motif might behave as a directing group towards the metal-catalyzed C-H bond activation in the benzamide site or in the anilide site. The impact and the consequences of such subtle control of site-selectivity are herein reviewed with important applications in carbon-carbon and carbon-heteroatom bond forming processes. The mechanisms unraveling these unique transformations are discussed in order to provide a better understanding for future developments in the field of site-selective C-H bond functionalization with transition metal catalysts.

Direct Hiyama Cross-Coupling of (Hetero)arylsilanes with C(sp2)-H Bonds Enabled by Cobalt Catalysis

We report a chelation-assisted C-H arylation of various indoles with sterically and electronically diverse (hetero)arylsilanes enabled by cost-effective Cp*-free cobalt catalysis. Key to the success of this strategy is the judicious choice of copper(II) fluoride as a bifunctional sliane activator and catalyst reoxidant. This methodology features a broad substrate scope and good functional group compatibility. The synthetic versatility of this protocol has been highlighted by the gram-scale synthesis and late-stage diversification of biologically active molecules.

Cu(II)-Mediated Cross-Dehydrogenative Coupling of Indolines with Sulfonamides, Carboxamides, and Amines

A facile and efficient Cu-mediated protocol for the cross-dehydrogenative coupling of indoline with sulfonamides, carboxamides, and anilines is reported. The reaction takes place through Cu-mediated C7-H activation via a 6-membered metallacycle to afford the amide and amine derivatives in good yields with a wide range of functional group tolerance. The importance of the protocol has been demonstrated by synthesizing the antiproliferative agent, ER-67836.

Rh(iii)-catalyzed C-7 arylation of indolines with arylsilanes via C-H activation

Site-selective synthesis of C-7 arylated indolines has been achieved via oxidative arylation of indolines with arylsilanes under Rh(iii)-catalyzed C-H activation of indolines by using CuSO4 as a co-oxidant. This transformation has been explored for a wide range of substrates under mild conditions.

Transition-metal-catalyzed site-selective C7-functionalization of indoles: advancement and future prospects

The advancement and future prospects of transition-metal-catalyzed auxiliary assisted regioselective C7-functionalization of indoles/indolines are covered in this article.

The controllable C2 arylation and C3 diazenylation of indoles with aryltriazenes under ambient conditions

The controllable C2 arylation and C3 diazenylation of indoles with aryltriazenes under ambient conditions was investigated.

A novel Pd-catalysed sequential carbonylation/cyclization approach toward bis-N-heterocycles: rationalization by electronic structure calculations

An unprecedented palladium-catalysed sequential aminocarbonylation/cyclization synthetic strategy, using carbon monoxide and structurally different aliphatic diamines as N-nucleophiles, gives access, in one pot, to a new family of indole-based N-heterocyclic derivatives (hydropyrazinones, benzodiazepinones and hydroquinoxalines). Optimization of the reaction conditions towards double carbonylation (P _CO = 30 bar, T = 80°C, iodoindole/diamine ratio = 1 : 1.5, toluene as solvent) allowed the target cyclic products, which are formed in situ via intramolecular cyclization of the ketocarboxamide intermediates, to be obtained through a nucleophilic addition/elimination reaction with the pendant terminal amine groups. The structure of the diamine nucleophile was revealed to affect the reaction's selectivity, with the best yields for the cyclic products being obtained in the presence of (1S,2S)-(+)-cyclohexane-1,2-diamine (a) as the nucleophile, using either 5- or 7-iodoindole as the substrate. The reaction's selectivity was rationalized based on electronic structure calculations, which explain the effect of the diamine structure on the predominant formation of the cyclic products.

Regioselective direct arylation of indoles on the benzenoid moiety

Recent advances in transition metal-catalyzed selective C–H functionalization of indoles have garnered tremendous attention.

Rhodium(iii)-catalyzed directed C–H benzylation and allylation of indoles with organosilicon reagents

Rhodium(iii)-catalyzed C2-benzylation and allylation of indoles with organosilicon reagents via chelation-assisted C–H activation has been developed.

Ar–P bond construction by the Pd-catalyzed oxidative cross-coupling of arylsilanes with H-phosphonates via C–Si bond cleavage

A novel and efficient methodology that allows for the construction of Ar–P bonds via the Pd-catalyzed oxidative cross-coupling reaction of various arylsilanes with H-phosphonates leading to valuable arylphosphonates has been developed.