Broad-Scope Rh-Catalyzed Inverse-Sonogashira Reaction Directed by Weakly Coordinating Groups

Regiodivergent C-H alkynylation of 2-arylthiazoles switched by RuII and PdII catalysis

Two complementary regiodivergent C-H alkynylations of 2-arylthiazoles are reported. When RuII catalysis is employed, an aryl ortho-alkynylation process is favored. The alkynylated products are gained in good yields. With the use of PdII catalysis, a thiazole C5-alkynylation process is developed, allowing for the construction of C5-alkynylated products. This strategy not only expands the methods for the functionalization of 2-arylthiazoles, but also provides new opportunities for the rapid assembly of complex molecular structures, which may have great potential in organic synthesis, medicinal chemistry, and materials science.

DLPNO-CCSD(T) and DFT study of the acetate-assisted C-H activation of benzaldimine at [RuCl2(p-cymene)]2: the relevance of ligand exchange processes at ruthenium(II) complexes in polar protic media

To gain mechanistic insights into the acetate-assisted cyclometallations of arylimines promoted by [RuCl2(p-cymene)]2 in polar protic media, DFT geometry optimizations (with M06 and ωB97X-D3 functionals and the cc-pVDZ-PP[Ru] basis set) followed by DLPNO-CCSD(T)/CBS energy evaluations were performed using benzaldimine as a model substrate and methanol as the solvent (with CPCM or SMD models). The calculation results show that coordination of the imine to an acetate ruthenium precursor is followed by anion (chloride or acetate) dissociation as the rate-determining step of the process. H-Bonding of two explicit MeOH to the anion reduces the calculated activation energy to ca. 23 kcal mol-1, in good agreement with the experimental half-life at room temperature. Subsequent AMLA/CMD C-H activation of the intermediate cationic complexes is a faster, reversible process. Alternative reaction pathways involving neutral diacetate ruthenium complexes offer AMLA/CMD transition state structures of lower energy but are precluded due to higher energy barriers for the initial ligand exchange processes at ruthenium. Solvent assistance accelerates the final chloride/acetate exchange processes on the cycloruthenate intermediates, particularly when compression in the condensed phase is taken into consideration. The performance of six DFT functionals (with the aug-pVTZ-PP[Ru] basis set) was assessed using the DLPNO-CCSD(T)/CBS reference energies. Neutral diacetate ruthenium complexes were incorrectly predicted as being kinetically relevant when using hybrid DFT methods (PBE0-D3(BJ), M06-2X or ωB97M-V). Good agreement between the calculated barrier heights and our benchmark energy results was obtained by using double-hybrid DFT methods. PWPB95 with D3(BJ) or D4 dispersion energy corrections was found to be the most accurate (ΔG≠ MUE of ca. 1 kcal mol-1). This study may aid our understanding of and help with further experimental investigations of synthetically useful carboxylate-assisted C-H bond functionalizations involving (N,C)-cyclometallated (p-cymene)Ru(II) intermediate complexes in sustainable polar protic solvents.

Palladium(II)-catalyzed annulation of N-methoxy amides and arynes: computational mechanistic insights and substituents effects

CONTEXT

The combined use of transition metal-catalyzed C-H activation with aryne annulation reactions has emerged as an important strategy in organic synthesis. In this study, the mechanisms of the palladium(II)-catalyzed annulation reaction of N-methoxy amides and arynes were computationally investigated by density functional theory. The role of methoxy amide as a directing group was elucidated through the calculation of three different pathways for the C-H activation step, showing that the pathway where amide nitrogen acts as a directing group is preferable. At the reductive elimination transition state, an unstable seven-membered ring is formed preventing the lactam formation. A substituent effect study based on an NBO analysis, Hammet, and using a More O'Ferall-Jenks plot indicates that the C-H activation step proceeds via an electrophilic concerted metalation-deprotonation (eCMD) mechanism. The results show that electron-withdrawing groups increase the activation barrier and contribute to an early Pd-C bond formation and a late C-H bond breaking when compared with electron-donating substituents. Our computational results are in agreement with the experimental data provided in the literature.

METHODS

All calculations were performed using Gaussian 16 software. Geometry optimizations, frequency analyses at 393.15 K, and IRC calculations were conducted at the M06L/Def2-SVP level of theory. Corrected electronic energies, NBO charges, and Wiberg bond indexes were computed at the M06L/Def2-TZVP//M06L/Def2-SVP level of theory. Implicit solvent effects were considered in all calculations using the SMD model, with acetonitrile employed as the solvent.

Ru(II)-Catalyzed Divergent C-H Alkynylation Cascade with Bifunctional α-Alcohol Haloalkynes

Native functionality directed the C-H activation cascade to enable rapid construction of molecular complexity, featuring step-economy and synthetic efficiency. Herein, by exploiting bifunctional α-alcohol haloalkynes, we developed Ru(II)-catalyzed carboxylic acid, amine, and amide assisted divergent C-H alkynylation and annulation cascade, affording polyfunctional heterocycles. Significantly, a bilateral aryl C-H polycyclization cascade of azobenzenes was achieved using the versatile haloalkynes.

Late-Stage C-H Activation of Drug (Derivative) Molecules with Pd(ll) Catalysis

This review comprehensively analyses representative examples of Pd(II)-catalyzed late-stage C-H activation reactions and demonstrates their efficacy in converting C-H bonds at multiple positions within drug (derivative) molecules into diverse functional groups. These transformative reactions hold immense potential in medicinal chemistry, enabling the efficient and selective functionalization of specific sites within drug molecules, thereby enhancing their pharmacological activity and expanding the scope of potential drug candidates. Although notable articles have focused on late-stage C-H functionalization reactions of drug-like molecules using transition-metal catalysts, reviews specifically focusing on late-stage C-H functionalization reactions of drug (derivative) molecules using Pd(II) catalysts are required owing to their prominence as the most widely utilized metal catalysts for C-H activation and their ability to introduce a myriad of functional groups at specific C-H bonds. The utilization of Pd-catalyzed C-H activation methodologies demonstrates impressive success in introducing various functional groups, such as cyano (CN), fluorine (F), chlorine (Cl), aromatic rings, olefin, alkyl, alkyne, and hydroxyl groups, to drug (derivative) molecules with high regioselectivity and functional-group tolerance. These breakthroughs in late-stage C-H activation reactions serve as invaluable tools for drug discovery and development, thereby offering strategic options to optimize drug candidates and drive the exploration of innovative therapeutic solutions.

Expedient C-H allylation of sulfoxonium ylides: merging C-H and C-C/C-het bond activation

Sulfoxonium ylide chelation-assisted C-H allylation of arenes has been accomplished utilizing strained vinyl carbo/heterocycles as the allyl surrogates via sequential C-H and C-C/het bond activation. Broad substrate scope, Co-catalysis, selectivity, and late-stage drug mutation are the important practical features.

Pd-Catalyzed Tandem Pathway for Stereoselective Synthesis of (E)-1,3-Enyne from β-Nitroalkenes by Using a Sacrificial Directing Group

The involvement of nitroalkenes instead of minimal one alkyne motif for (E)-1,3-enynes synthesis through a palladium catalyzed stereoselective bond forming pathway at room temperature is presented. Implication of nitro group as a sacrificial directing group, formation of magical alkyne on a newly developed Csp 3 -Csp 3 bond with initial palladium-MBH adduct make this methodology distinctive. This protocol features an unprecedented sequential acetate addition, carbon-carbon bond formation, isomerization of double bond and nitromethane degradation in a tandem catalytic walk via dancing hybridization. Mechanistic understanding through identification of intermediates and computational calculations furnishes complete insight into the tandem catalytic pathway. Broad substrates scope and functional groups tolerance make this synthetic methodology magnificent and dynamic. This represents the first example of stereoselective 1,3-enyne synthesis exclusively from alkene substrates by introducing the concept of sacrificial directing group.

Directing group assisted para-selective C-H alkynylation of unbiased arenes enabled by rhodium catalysis

Regioselective C-H alkynylation of arenes via C-H activation is challenging yet a highly desirable transformation. In this regard, directing group assisted C(sp2)-H alkynylation of arenes offers a unique opportunity to ensure precise regioselectivity. While the existing methods are mainly centered around ortho-C-H alkynylation and a few for meta-C-H alkynylation, the DG-assisted para-selective C-H alkynylation is yet to be reported. Herein we disclose the first report on Rh-catalyzed para-C-H alkynylation of sterically and electronically unbiased arenes. The para-selectivity is achieved with the assistance of a cyano-based directing template and the selectivity remained unaltered irrespective of the steric and electronic influence of the substituents. The post-synthetic modification of synthesized para-alkynylated arenes is also demonstrated. The mechanistic intricacies of the developed protocol are elucidated through experimental and computational studies.

Ru(II)-Catalyzed Weakly Coordinating Carbonyl-Assisted Dialkynylation of (Hetero)Aryl Ketones

Functionalized aryl(heteroaryl) ketones are present in many natural products as key structural components and serve as basic synthetic building blocks for various organic transformation reactions. Therefore, the development of an effective and sustainable route for making these classes of compounds remains challenging yet highly desirable. Herein, we report a simple and efficient catalytic system for dialkynylation of aromatic/heteroaromatic ketones via a double C-H bond activation in the presence of less expensive ruthenium(II)-salt as a catalyst using the weakly and native carbonyl group as the desired directing group. The developed protocol is highly compatible, tolerant, and sustainable toward various functional groups. The synthetic utility of the developed protocol has been demonstrated through the scale-up synthesis and functional group transformation. Control experiments support the involvement of the base-assisted internal electrophilic substitution (BIES) reaction pathway.

Catalytic C-H alkynylation of benzylamines and aldehydes with aldimine-directing groups generated in situ

Iridium-catalysed regioselective C-H alkynylation of unprotected primary benzylamines and aliphatic aldehydes has been achieved using in situ-installed aldimine directing groups. This protocol provides a straightforward route for the synthesis of the alkynylated primary benzylamine and aliphatic aldehyde derivatives, featuring good substrate compatibility and high regioselectivity.

Mechanistic Insights Into the Rhodium-Catalyzed C-H Alkenylation/Directing Group Migration and [3+2] Annulation: A DFT Study

The mechanism of the rhodium-catalyzed C-H alkenylation/directing group migration and [3+2] annulation of N-aminocarbonylindoles with 1,3-diynes has been investigated with DFT calculations. On the basis of mechanistic studies, we mainly focus on the regioselectivity of 1,3-diyne inserting into the Rh-C bond and the N-aminocarbonyl directing group migration involved in the reactions. Our theoretical study uncovers that the directing group migration undergoes a stepwise β-N elimination and isocyanate reinsertion process. As studied in this work, this finding is also applicable to other relevant reactions. Additionally, the role of Na⁺ versus Cs⁺ involved in the [3+2] cyclization reaction is also probed.

Unlocking Regiodivergence in PdII- and RhIII-Mediated Site-Selective C-H Bond Alkynylation of Imidazopyridines

An efficient Pd^II- and Rh^III-controlled site-selective C-H bond alkynylation of imidazopyridines using (bromoethynyl)triisopropylsilane is disclosed. The divergent methodology allows straightforward access to a wide range of products alkynylated at the C3 and ortho positions. This strategy is suggestive of a practical platform that can be suitable for late-stage diversification and may assist in the design of more selective and complementary catalytic systems.

Weak-Chelation Assisted Cobalt-Catalyzed C-H Bond Activation: An Approach Toward Regioselective Ethynylation of N-Aryl γ-Lactam

The sustainable C-H bond ethynylation of N-aryl γ-lactam has been achieved in a highly regioselective manner. In this protocol, earth-abundant cobalt(III)-catalyst was found to be effective, triggering the C-H metalation using a weakly coordinating lactam group. Herein, the ortho-(sp²)-H ethynylation has been obtained regioselectively. The mechanistic studies reveal the non-involvement of the radical pathway for this conversion. However, the parallel kinetic isotope experiment suggests that the C-H bond activation is involved in the rate-determining step. In addition, the synthetic utility of ethynylated N-aryl γ-lactam has been demonstrated for many useful transformations.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Copper adorned magnetic nanoparticles as a heterogeneous catalyst for Sonogashira coupling reaction in aqueous media

A nanomagnetic hydrophilic heterogeneous copper catalyst, termed γ-Fe₂O₃@PEG@PAMAM G₀-Cu, has been successfully prepared and characterized using FT-IR, XRD, FE-SEM, TEM, EDX, mapping, TGA/DTG, VSM and ICP analyses. The catalyst displayed excellent activity for the palladium-free Sonogashira cross coupling reaction of various aryl iodides and bromides with phenylacetylene derivatives in pure water. The presence of polyethylene glycol coupled with hydrophilic character of the Cu-catalyst adorned on γ-Fe₂O₃ MNPs provides the ready dispersion of the catalyst particles in water, leading to higher catalytic performance as well as facile catalyst recovery via simple magnetic decantation. The recovered catalyst was reused for at least six successive runs with little reduction in its catalytic activity and any noticeable changes in its structure. The use of water as a green solvent, without requiring any additive or organic solvent, as well as the exploitation of abundant and low-cost copper catalyst instead of expensive Pd catalyst along with the catalyst recovery and scalability, make this method favorable from environmental and economic points of view for the Sonogashira coupling reaction.

Ru(II)-catalyzed external auxiliary-free primary amide-directed inverse Sonogashira reaction on (hetero)arylamides

Herein, we report ruthenium(II)-catalyzed weakly coordinating primary amide-assisted ortho-di-alkynylation of (hetero)arylamides via double C-H bond activation in the presence of bromo-alkynes as coupling partners. The attractive features of the developed strategy lie in the usage of an inexpensive ruthenium(II)-salt, external auxiliary-free directing group and simple reaction conditions, along with a broad substrate scope, high reaction yields and scale-up synthesis.

Rh(III)-Catalyzed C-H Activation/Annulation of Benzohydroxamates and 2-Imidazolones: Access to Urea-Fused-Dihydroisoquinolone Scaffolds Reminiscent of Pyrrole Alkaloid Natural Products

A Rh(III)-catalyzed C-H activation/annulation with an imidazolone as alkene partner is reported to access dihydroisoquinolone-fused imidazolin-2-ones. These bicycles are reminiscent of scaffolds belonging to the pyrrole alkaloid family of natural products. This approach facilitates construction of a variety of urea-fused dihydroisoquinolone scaffolds including heterocyclic moieties.

Cocrystal Formation Precedes the Mechanochemically Acetate-Assisted C-H Activation with [Cp*RhCl2 ]2

This work reports the experimentally studied mechanochemical formation of rhodacycles by ball milling pyridine- and quinoline-derived substrates and [Cp*RhCl₂ ]₂ in the presence of NaOAc. Ex-situ analysis of the mechanochemical reactions using powder X-ray diffraction (PXRD), solid-state UV-vis spectroscopy and ATR-FTIR spectroscopy revealed the formation of unexpected cocrystals between the substrates and the rhodium dimer prior to the C-H activation step. This sequence of events differs from the generally accepted steps in solution in which cleavage of [Cp*RhCl₂ ]₂ is initiated by acetate ions. Additionally, the mechanochemical approach enabled the synthesis of the six-membered rhodacycle [Cp*Rh(2-benzilpyridine)Cl], a metal complex repeatedly reported as inaccessible in solution. Altogether, the results of this investigation clarify some of the fundamental aspects of mechanochemical cyclometallations.

Palladium-Catalyzed Alkynylation of Enones with Alkynylsilanes via C-C Bond Activation

We report herein the synthesis of 1,3-enynes via palladium-catalyzed cross-coupling between enone derivatives and alkynylsilanes. The employment of an appropriate pyridine-oxazoline ligand is the key to the C-C cleavage and the high E/Z stereoselectivity. This protocol features broad substrate scope and wide functional-group tolerance, affording the desired products in moderate-to-good yields. Late-stage diversification of natural product β-ionone further demonstrated the synthetic utility of this protocol.

Metal-catalyzed asymmetric heteroarylation of alkenes: diverse activation mechanisms

This review summarizes the state-of-the-art in transition metal-catalyzed asymmetric alkylation of heteroarenes using alkenes (covering literature from 2000 to late 2021). Based on elementary reactions on metals for substrate activation, these reactions are broadly classified in several categories: (A) concerted oxidative addition of heteroaryl C-H bonds on rhodium(I) and iridium(I), (B) ligand-to-ligand hydrogen transfer (LLHT) on low-valent 3d metal complexes of nickel and cobalt, (C) different ways for deprotonation of heteroaryl C-H bonds by late transition metal complexes, especially palladium, including electrophilic aromatic substitution and a related mechanism, base-assisted intramolecular electrophilic substitution, concerted and nonconcerted metalation deprotonation, (D) σ-bond metathesis by d⁰ early transition metal complexes, (E) electrophilic activation of olefins by Pd(II), Pt(II) and Au(I), and (F) metal hydride insertion of aryl olefins and dienes. The demand to achieve enantiocontrol in the heteroarylation reactions has also driven innovation in chiral ancillary ligands, exemplified by extremely bulky, chiral N-heterocyclic carbenes for nickel catalysts, bulky monodentate oxazolines for Wacker-type reactions and chiral cyclopentadienyl ligands for half-sandwich complexes of scandium.

Cp*Rh(III)-Catalyzed Regioselective C(sp2)-H Mono- and Dialkynylation of Thioamides by Sulfur Coordination

An efficient Cp*Rh(III)-catalyzed regioselective C(sp²)-H mono- and dialkynylation of thioamides was described. This reaction was performed under mild conditions in high yields (up to 98%) with a broad substrate scope. Significantly, the versatility of this method was further demonstrated by controlled mono- and dialkynylation. Application of this protocol in the late stage functionalization of two drug molecules (Adapalene and Amoxapine) was also demonstrated.

Thioether-directed Rh(III)-catalyzed peri-selective acyloxylation of arenes

A thioether directed acyloxylation of arenes has been realized via Cp*Rh(III)-catalyzed C-H activation and subsequent coupling with carboxylic acids. This new method showed high functional group compatibility and broad substrate scope. Primary mechanistic studies have been conducted and a tentative reaction mechanism was proposed. It represents the first example of a thioether-directed Cp*Rh(III)-catalyzed C(sp²)-H acyloxylation reaction.

Photoinduced inverse Sonogashira coupling reaction

A transition-metal and photocatalyst-free, photoinduced inverse Sonogashira coupling reaction was developed. Under visible-light irradiation, the excited state iodoalkyne acted as an “alkynyl radical synthetic equivalent”.

Directing Group Assisted Rhodium Catalyzed meta-CH Alkynylation of Arenes

Site-selective C-H alkynylation of arenes to produce aryl alkynes is a highly desirable transformation due to its prevalence in various natural products, drug molecules and in material sciences. To ensure...

Experimental and Computational Studies on the Acetate-Assisted C-H Activation of N-Aryl Imidazolium Salts at Rhodium and Iridium: A Chloride Additive Changes the Selectivity of C-H Activation

Combined experimental and computational mechanistic studies of the reactions of unsymmetrical, para-substituted N-aryl imidazolium salts, L2-R₁,R₂, at [MCl₂Cp*]₂ (M = Rh, Ir) in the presence of NaOAc are reported. These proceed via intermediate N-heterocyclic carbene complexes that then allow an internal competition between two differently substituted aryl rings toward C-H activation to be monitored. At 348 K in dichloroethane C-H activation of the aryl with the more electron-withdrawing substituents is generally favored. DFT calculations show similar barriers for proton transfer and dissociative HOAc/Cl^- ligand substitution, with proton transfer favoring electron-donating substituents, and ligand substitution favoring electron-withdrawing substituents. Microkinetic simulations reproduce the experimental preference implying that the ligand substitution step dominates selectivity. For several substrates, notably L2-F,OMe and L2-F,H, running the C-H activation reactions at 298 K in the presence of added [Et₄N]Cl reverses the selectivity. The greater availability of chloride in solution makes an alternative dissociative interchange ligand substitution mechanism accessible, leaving proton transfer as selectivity determining and so favoring electron-donating substituents. Our results highlight the potential importance of the ligand substitution step in the interpretation of substituent effects and demonstrate how a simple additive, [Et₄N]Cl, can have a dramatic effect on selectivity by changing the mechanism of ligand substitution.

Redox-Neutral Vicinal Difunctionalization of Five-Membered Heteroarenes with Dual Electrophiles

A new reaction mode of palladium/norbornene (Pd/NBE) cooperative catalysis is reported involving the selective coupling of two different carbon-based electrophiles for vicinal double C-H functionalization of five-membered heteroarenes in a site-selective and redox-neutral manner. The key is to use alkynyl bromides as the second electrophile, which allows vicinal difunctionalization of a wide range of heteroarenes including pyrroles, thiophenes and furans at their C4 and C5 positions. One- or two-step tetrafunctionalizations of simple pyrrole and thiophene have also been realized. The C2-substituted NBEs prove most effective in these reactions, and the mechanistic exploration discloses the origin of the high selectivity of this transformation. Synthetic utility of this method has been exemplified in the concise preparations of thiophene-containing organic materials and a protein kinase inhibitor analogue. Preliminary success has also been achieved in a direct annulation event, using a tethered ketone as the second electrophile.

Rhodium-catalysed ortho-alkynylation of nitroarenes

The ortho-alkynylation of nitro-(hetero)arenes takes place in the presence of a Rh(iii) catalyst to deliver a wide variety of alkynylated nitroarenes regioselectively. These interesting products could be further derivatized by selective reduction of the nitro group or palladium-catalysed couplings. Experimental and computational mechanistic studies demonstrate that the reaction proceeds via a turnover-limiting electrophilic C-H metalation ortho to the strongly electron-withdrawing nitro group.

Rhodium(iii)-catalyzed synthesis of trisubstituted furans via vinylic C-H bond activation

We report an Rh(iii)-catalyzed one-pot synthesis of trisubstituted furan derivatives through C_vinyl-H activation of α,β-unsaturated ketones with acrylates. The control study revealed that the Heck-type product obtained undergoes Paal-Knorr type cyclization in the presence of an Ag salt. Hence, the Ag salt plays a dual role of a halide scavenger and a Lewis acid catalyst for Paal-Knorr type cyclization. The furan product can be transferred into the respective alcohol and acid derivatives which are useful intermediates in synthesizing biologically active molecules.

Ruthenium(ii)-catalyzed regioselective direct C4- and C5-diamidation of indoles and mechanistic studies

A ruthenium(ii)-catalyzed regioselective direct diamidation of 3-carbonylindoles at the C4- and C5-positions using various dioxazolones is described. This novel protocol allows for the effective installation of two amide groups on the benzene ring in indole. A remarkably broad substrate scope, excellent functional group tolerance, and mild reaction conditions are notable features of this protocol. Further explorations reveal that benzo[b]thiophene-3-carboxaldehyde is a viable substrate and affords its corresponding diamidation products. The diamido indoles are further converted into various functionalized products and used as sensors for metal ion detection. Density functional theory studies are also conducted to propose a reaction mechanism and provide a detailed understanding of the regioselectivity observed in the reaction.

Ruthenium(ii)-catalyzed regioselective C4-/C5-diamidation of 3-carbonylindoles is described and a DFT study is conducted to understand the observed regioselectivity and the mechanism.

Cascade Reaction to Selectively Synthesize Multifunctional Indole Derivatives by IrIII -Catalyzed C-H Activation

An effective and condition-controlled way to synthesize with high selectivity a variety of functionalized indoles with potent biological properties has been developed. Notably, 2,4-dialkynyl indole products were obtained by direct double C-H bond alkynylation, whereas alkynyl at the C4 position could convert to carbonyl to generate 2-alkynyl-3,4-diacetyl indoles fast and effectively. Additionally, a one-pot relay catalytic reaction led to 2,5-di-alkynyl-3,4-diacetyl indoles when using a carbonyl group as the directing group and by controlling the type and quantity of additives. A possible mechanism was proposed based on many studies including deuterium-exchange experiments, the necessary conditions of product conversion, and the effect of water on the reaction.

Ruthenium-Catalyzed Regioselective C(sp2)-H Activation/Annulation of N-(7-Azaindole)amides with 1,3-Diynes Using N-Amino-7-azaindole as the N,N-Bidentate Directing Group

The ruthenium(II)-catalyzed regioselective annulation of N-(7-azaindole)amides with 1,3-diynes has been demonstrated. Bioactive N-amino-7-azaindole has been used as a new bidentate directing group to furnish an array of 3-alkynylated isoquinolones. Furthermore, the developed protocol works efficiently for both aryl- and heteroaryl-substituted amides producing a range of pharmacologically useful 7-azaindole-based isoquinolones with a wide range of functionality.

Tetrasubstituted 1,3-Enynes by Gold-Catalyzed Direct C(sp2)-H Alkynylation of Acceptor-Substituted Enamines

A gold-catalyzed synthesis of tetrasubstituted 1,3-enynes from hypervalent iodine(III) reagents and activated alkenes is reported. This reaction involves an in situ formed alkynyl Au(III) species and a subsequent direct C(sp²)-H functionalization of alkenes, offering 26 enynes in 62-92% yield with excellent functional group tolerance.

Mechanochemical Solvent-Free Catalytic C-H Methylation

The mechanochemical, solvent-free, highly regioselective, rhodium-catalyzed C-H methylation of (hetero)arenes is reported. The reaction shows excellent functional-group compatibility and is demonstrated to work for the late-stage C-H methylation of biologically active compounds. The method requires no external heating and benefits from considerably shorter reaction times than previous solution-based C-H methylation protocols. Additionally, the mechanochemical approach is shown to enable the efficient synthesis of organometallic complexes that are difficult to generate conventionally.