Rhodium-Catalyzed Hydrogen-Releasingortho-Alkenylation of 7-Azaindoles

Synthesis of 1H-Isoindoles via Ruthenium(II)-Catalyzed Cyclization of Benzimidates with Alkenes

A Ru(II)-catalyzed efficient synthesis of 1H-isoindoles via the cyclization of benzimidates with alkenes has been demonstrated. This methodology exhibits high compatibility with various functionalized activated and unactivated olefins containing different sensitive functional groups. This protocol provides an effective method for synthesizing various 1H-isoindole derivatives in decent to excellent yields. Notably, the ortho-alkenylation of benzimidates with unactivated alkenes was achieved. A potential reaction mechanism has been suggested that involves C-H activation, 1,2 insertion, and β-hydride elimination subsequent to aza-Michael addition.

Redox-Neutral Ru(0)-Catalyzed Alkenylation of 2-Carboxaldimine-heterocyclopentadienes

A new Ru₃(CO)₁₂-catalyzed directed alkenylation of 2-carboxaldimine-heterocyclopentadienes has been accomplished. This process allows coupling of furan, pyrrole, indole, and thiophene 2-carboxaldimines with electron-poor alkenes such as acrylates, vinylsulfones, and styrenes. This regio- and chemoselective oxidative C-H coupling does not require the presence of an additional sacrificial oxidant. Density functional theory calculations allowed us to propose a mechanism and unveiled the nature of the H₂ acceptor.

Pd and photoredox dual catalysis assisted decarboxylative ortho-benzoylation of N-phenyl-7-azaindoles

Directing group assisted decarboxylative ortho-benzoylation of N-aryl-7-azaindoles with α-keto acids has been achieved by synergistic visible light promoted photoredox and palladium catalysis. The approach tenders rapid entry to aryl ketone...

Regioselective C-H Functionalization of the Six-Membered Ring of the 6,5-Fused Heterocyclic Systems: An Overview

The regioselective C-H functionalization of the five-membered ring of the 6,5-fused heterocyclic systems is nowadays well documented due to its high reactivity compared to the six-membered ring. So, developing new procedures of C-H functionalization of the six-membered ring "by thinking out of the box" is extremely challenging, which explains the limited number of reports published to date. This review paper aims to highlight advances achieved in this emerging chemistry research and discusses recently reported methods.

Rhodium-catalysed direct formylmethylation using vinylene carbonate and sequential dehydrogenative esterification

A rhodium-catalysed direct formylmethylation adopting vinylene carbonate as an ethynol equivalent is reported. The developed catalytic system is further utilised for the oxidant-free production of esters with the liberation of hydrogen gas. Some control experiments are conducted to elucidate the reaction mechanism.

Copper-catalyzed ortho-selective direct sulfenylation of N-aryl-7-azaindoles with disulfides

A copper-catalyzed direct C-H chalcogenation of N-aryl-azaindoles with disulfides is described. This transformation was performed using Earth abundant Cu(OAc)₂ as a catalyst, benzoic acid as an additive, air as a terminal oxidant, and readily available diaryl and dialkyldisulfides (or diselenide) as chalcogenation reagents. High functional group tolerance and excellent regioselectivity are demonstrated by the efficient preparation of a wide range of ortho-sulfenylation-7-azaindoles.

Rhodium-Catalyzed Redox-Neutral Olefination of Aryldiazenes with Acrylate Esters via C-H Activation and Transfer Hydrogenation

Rh(III)-catalyzed redox-neutral C-H olefination of aryldiazenecarboxylates has been realized using arylate esters as the olefinating reagents. This reaction proceeds under mild and redox-neutral conditions, resulting in integration of C-H activation and transfer hydrogenation. The chemoselectivity complements that of previously reported rhodium-catalyzed coupling of the same substrates.

Synthesis of rhodium(iii)-catalyzed isoquinoline derivatives from allyl carbonates and benzimidates with hydrogen evolution

A novel Rh(iii)-catalyzed cascade C-H activation/cyclization approach to access isoquinoline derivatives from benzimidates and available allyl carbonates with the liberation of H2 has been realized. Allyl carbonates were first used as a versatile and universal C2 synthon to synthesize this biological activity skeleton via an efficient and practical process just within 1 h.

Dehydrogenative Coupling of Benzylic and Aldehydic C-H Bonds

A photoinduced dehydrogenative coupling reaction between benzylic and aldehydic C-H bonds is reported. When a solution of an alkylbenzene and an aldehyde in ethyl acetate is irradiated with visible light in the presence of iridium and nickel catalysts, a coupled α-aryl ketone is formed with evolution of dihydrogen. An analogous C-C bond forming reaction occurs between a C-H bond next to the nitrogen of an N-methylamide and an aldehydic C-H bond to produce an α-amino ketone. These reactions provide a straightforward pathway from readily available materials leading to valued structural motifs of pharmacological relevance.

Iridium-Catalyzed Cross-Coupling Reactions of Alkenes by Hydrogen Transfer

A range of Ru-, Rh-, or Pd-catalyzed vinylic C-H/C-H cross-coupling reactions of olefins have been demonstrated to provide 1,3-dienes, using a quantitative amount of metal oxidants. Although transfer hydrogenation and C-H alkenylation are two important areas that evolved independently, we herein report the first iridium-catalyzed cross-coupling reactions of alkenes by integration of directed C(alkenyl)-H alkenylation and transfer hydrogenation to obviate the usage of a metal oxidant, employing a hydrogen acceptor such as inexpensive chloranil.

Rhodium(III)-Catalyzed Regioselective C(sp2)-H Functionalization of 7-Arylpyrazolo[1,5-a]pyrimidines with Dioxazolones as Amidating Agents

Rh(III)-catalyzed C-H functionalization of 7-arylpyrazolo[1,5-a]pyrimidines was developed wherein the pyrazolo[1,5-a]pyrimidine moiety is reported for the first time to direct the C-H bond activation. Various 7-arylpyrazolo[1,5-a]pyrimidines underwent smooth C-H amidation with alkyl-, aryl-, and heteroaryl-substituted dioxazolones to afford the products in moderate to good yields. Mechanistic studies suggest that a six-membered rhodacycle intermediate involving N1 might play a key role in the regioselective catalytic cycle.

Oxidative R1-H/R2-H Cross-Coupling with Hydrogen Evolution

Oxidative R¹-H/R²-H cross-coupling with hydrogen evolution serves as one of the most atom-economical methods for constructing new chemical bonds. This reaction strategy avoids substrate prefunctionalization steps in traditional cross-coupling reactions. Besides, hydrogen gas, which is recognized as a source of green energy, is the only byproduct during the reaction process. The major challenge in this reaction strategy is to achieve selective bond formation and hydrogen evolution at the same time. Over the past few years, novel synthetic techniques especially photochemistry and electrochemistry have provided possibilities for oxidative cross-coupling with H₂ liberation. Both C-C and C-X bonds can be constructed without the use of any sacrificial reagents. In this perspective, we will discuss the concept of this reaction strategy and give an overview of its recent development.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Divergent Coupling of Anilines and Enones by Integration of C-H Activation and Transfer Hydrogenation

Cp*Rh^III /Ir^III complexes are known to play important roles in both C-H activation and transfer hydrogenation (TH). However, these two areas evolved separately. They have been integrated in redox- and chemodivergent coupling reactions of N-pyridylanilines with enones. The iridium-catalyzed coupling with enones leads to the efficient synthesis of tetrahydroquinolines through TH from ⁱ PrOH. Counterintuitively, ⁱ PrOH does not serve as the sole hydride source, and the major reaction pathway involves disproportionation of a dihydroquinoline intermediate, followed by the convergent and iterative reduction of quinolinium species.

Ru(II)-Catalyzed C-H Aminocarbonylation of N-(Hetero)aryl-7-azaindoles with Isocyanates

The ruthenium(II)-catalyzed C-H aminocarbonylation of N-(hetero)aryl-7-azaindoles with isocyanates is described. The excellent site selectivity at the ortho-position within the N-(hetero)aryl ring was observed to provide ortho-amidated N-(hetero)aryl-7-azaindoles under the mild reaction conditions. The resulting 7-azaindole derivatives can be readily transformed into 7-azaindoles containing carboxylic acid and alkyl amine functional groups.

Iridium-catalyzed C–H phosphoramidation of N-aryl-7-azaindoles with phosphoryl azides

An iridium-catalyzed C–H phosphoramidation of N-aryl-7-azaindoles with phosphoryl azides was developed, affording a series of 7-azaindole phenylphosphoramidates.