C-H Activation and Alkyne Annulation via Automatic or Intrinsic Directing Groups: Towards High Step Economy

CuBr-Catalyzed Coupling of Propargyl Bromides with Terminal Alkynes: Syntheses of 1,4-Diynes and Alkynyl Shift Access to Unsymmetrical 1, n-Diynes

A CuBr-catalyzed cross-coupling reaction of propargyl bromides with terminal alkynes for the synthesis of 1, n-diynes was investigated. In N,N-dimethylacetamide (DMAc), the cross-coupling reactions of 3-bromo-1-arylpropynes, 3-bromo-1-phenyl-butyne/pentyne with aromatic terminal alkynes in the presence of CuBr and K3PO4 under nitrogen at 40 °C occur to give 1, 5-diaryl-1, 4-diynes having 3-CH2/3-CHMe/3-CHEt/3-CHiPr moieties with high chemoselectivity. Under similar reaction conditions, either the reactions of 3-bromo-1-arylpropynes with aliphatic terminal alkynes or the reactions of 3-bromo-1-alkylpropynes with aromatic terminal alkynes afforded the unexpected unsymmetric 1, 4-disubstituted 1, 3-diynes through one of the alkynyl group shifts to the side conjugating with the aryl group; in these cases, 1, 5-disubstituted 1, 4-diynes could not be obtained at all. In addition, when 3-bromo-1-phenyl-butynes react with aliphatic terminal alkynes bearing a distal phenyl group, the formed 1, 4-diynes are expected not to undergo the alkynyl group shift due to the methyl group at 3-position to form 1, 3-diynes; however, 1, 4-diynes could not be obtained either, and the 1, 5-, 1, 6-, and 1, 7-diynes, by an unprecedented remote alkynyl shift to the side conjugating with the aryl group, were isolated from the reaction mixtures in good yields.

Synthesis of acridones via Ir(III)-catalyzed amination annulation of oxazoles with anthranils

An unprecedented Ir(III)-catalyzed C-H activation/amination/annulation of 2-phenyloxazoles with anthranils for the highly selective preparation of acridone derivatives in one-pot under controlled conditions is reported. This protocol is characterized by atom economy and high regioselectivity. A wide range of anthranils with 2-phenyloxazoles were well tolerated and afforded the desired products in moderate to good yields, in which the anthranil serves as a convenient amination reagent.

Microwave-Assisted Ru(II)-Catalyzed Regioselective Methyl Acylation of 2-Arylbenzoazoles: Synthesis of Benzofuran Conjugates via C-H Activation/Annulation

An efficient Ru(II)-catalyzed C-H functionalization protocol for 2-arylbenzoazoles as the directing group and sulfoxonium ylide has been developed. Gratifyingly, concomitant annulation was observed when 3-(benzo[d]azol-2-yl) phenol was used, enabling the construction of benzofuran conjugates. Notably, the utilization of water as the solvent and an energy efficient approach makes the reaction greener, contributing to overall sustainability. This protocol exhibits excellent scalability up to the gram scale with a diverse array of substitutions. Furthermore, the mechanism was examined by ESI-MS, and photophysical studies were also performed.

Switchable Regioselective C-H Activation/Annulation of Acrylamides with Alkynes for the Synthesis of 2-Pyridones

A catalyst-based switchable regioselective C-H activation/annulation of acrylamides with propargyl carbonates has been developed, delivering C5 or C6 alkenyl substituted 2-pyridones. This robust protocol proceeds with a broad substrate scope and good functional group tolerance under redox-neutral reaction conditions. More significantly, this reaction is highly effective with previously challenging unsymmetrical alkynes, including unbiased alkyl-alkyl substituted alkynes, with perfect and switchable regioselectivity. Additionally, mechanistic studies and DFT calculations were performed to shed light on the switchable regioselectivity.

Biorelevant Weakly Coordinating Directing Group Assisted C-H Alkenylation with Cyclopropanols via Sequential C-H/C-C Activation

A weakly coordinating biorelevant intrinsic directing group (DG) assisted site-selective C-H alkenylation via sequential C-H/C-C bond activation has been accomplished under Ru(II)-catalysis using readily accessible cyclopropyl alcohol as an alkenyl surrogate. Utilization of an intrinsic DG, exclusive regioselectivity, functional group diversity, late-stage natural product and drug mutations are the important practical features.

Mechanistic insights into an NH4OAc-promoted imine dance in Rh-catalysed multicomponent double C-H annulations through an N-retention/exchange dual channel

Developing new and understanding multicomponent reactions (MCRs) is an appealing but challenging task. Herein, Rh(iii)-catalyzed multicomponent double C-H annulations of cyclic diimines (or diketones and acetone), alkynes, and ammonium acetate to assemble functionalized 1,1'-biisoquinolines and C-bridged 1,1'-bisisoquinolines with controllable 14N/15N editing in one shot has been developed. Through a combination of isotopic-labeling (2H, 18O, and 15N) experiments, crystallography, and time-dependent ESI-MS, the reaction process was studied in detail. Ammonium acetate accounts for two rounds of Hofmann elimination and iminization, thus leading to an unprecedented imine dance, cyclic imine → N-alkenyl imine → NH imine. The N-alkenyl imine can immediately guide a C-H annulation (N-retention channel), and some of it is converted into NH-imine to trigger another annulation (N-exchange channel). The channels and 15N ratios can be regulated by the reaction mode and acidity. Moreover, the resulting 1,1'-biisoquinolines are a privileged ligand scaffold which is exemplified herein by a hydrazine-iodine exchange reaction to form drug-like benzo[c]cinnolines.

Enaminone-directed ruthenium(II)-catalyzed C-H activation and annulation of arenes with diazonaphthoquinones for polycyclic benzocoumarins

The weakly coordinating enaminone functionality has been leveraged for a C-H bond activation strategy under ruthenium catalysis and employed in the regioselective annulative coupling of arenes with diazonaphthoquinones, offering polycyclic benzocoumarins in very high yields. The enaminone motif plays a dual role and the protocol operates through a Ru(II)/Ru(IV) catalytic pathway which is amenable to the diversification of various pharmacophore-coupled substrates.

Recent advances in metal directed C-H amidation/amination using sulfonyl azides and phosphoryl azides

Transition metal-catalyzed C-N bond formation reactions have gained popularity as a method for selectively transforming common C-H bonds into N-functionalized molecules. This approach is particularly useful for synthesizing aminated molecules, which require aminating reagents and amidated building blocks. Over the past two decades, significant advancements have been achieved in transition-metal-catalyzed C-H functionalization, with organic azides emerging as promising amino sources and internal oxidants. This review focuses on recent developments in utilizing sulfonyl and phosphoryl azides as building blocks for directed intra- and intermolecular C-H functionalization reactions. Specifically, it discusses methods for synthesizing sulfonamidates and phosphoramidates using sulfonyl and phosphoryl azides, respectively. The article highlights the potential of C-H functionalization reactions with organic azides for efficiently and sustainably synthesizing N-functionalized molecules, providing valuable insights into the latest advancements in this field.

Synthesis of Cyclopenta[c]quinolines by Palladium-Catalyzed Cyclization of 3-Bromoindoles with Internal Alkynes via Spirocyclic Cyclopentadiene Intermediates

A novel method for the construction of a cyclopenta[c]quinoline ring via cyclization of 3-bromoindoles with internal alkynes in the presence of palladium is described. The formation of the cyclopenta[c]quinoline ring is proposed from a double [1,5] carbon sigmatropic rearrangement of the spirocyclic cyclopentadiene intermediate, which is generated in situ from the cyclization of 3-bromoindoles with internal alkynes involving a sequential double alkyne insertion into the carbon-palladium bond and dearomatization of indole. The present studies have developed a novel ring-expansion reaction of the pyrrole ring to pyridine via one carbon insertion into the C2-C3 bond of indoles and provided a simple and distinct route for the construction of tricyclic fused-quinoline derivatives that are not easy to access with conventional methods.

Propargyl Alcohols as Bifunctional Reagents for Divergent Annulations of Biphenylamines via Dual C-H Functionalization/Dual Oxidative Cyclization

The C-H functionalization strategy provides access to valuable molecules that previously required convoluted synthetic attempts. Dual C-H unsymmetrical functionalization, with a single bifunctional reagent, is an effective tactic. Propargyl alcohols (PAs), despite containing a reactive C≡C bond, have not been explored as building blocks via oxidative cleavage. Annulations via C-H activation are a versatile and synthetically attractive strategy. We disclose PA as a new bifunctional reagent for unsymmetrical dual C-H functionalization of biphenylamine for regioselectively annulated outcomes. On tuning the conditions, the annulation bifurcated towards an unusual dual oxidative cyclization. This method accommodates a wide range of PAs and showcases late-stage diversification of some natural products.

Palladium-Catalyzed C(sp3)-H Biarylation of 8-Methyl Quinolines with Cyclic Diaryliodonium Salts to Access Functionalized Biaryls and Fluorene Derivatives

Herein, we have developed the cyclic diaryliodonium salts as biarylating agents in the C(sp³)-H functionalization using 8-methyl quinoline as the intrinsic directing group. The oxidant-free reaction produces a vast array of the biarylated products with iodo functionality that can be further functionalized. Additionally, intramolecular C(sp³)-H functionalization in a stepwise manner under palladium-catalyzed conditions produced the fluorene derivatives in excellent yields.

Diverse reactivity of alkynes in C-H activation reactions

Alkynes occupy a prominent role as a coupling partner in the transition metal-catalysed directed C-H activation reactions. Due to low steric requirements and linear geometry, alkynes can effectively coordinate with metal d-orbitals. This makes alkynes one of the most successful coupling partners in terms of the number of useful transformations. Remarkably, by changing the reaction conditions and transition-metals from 5d to 3d, the pattern of reactivity of alkynes also changes. Due to the varied reactivity of alkynes, such as alkenylation, annulation, alkylation, and alkynylation, they have been extensively used for the synthesis of valuable organic molecules. Despite enormous explorations with alkynes, there are still a lot more possible ways by which they can be made to react with M-C bonds generated through C-H activation. Practically there is no limit for the creative use of this approach. In particular with the development of new high and low valent first-row metal catalysts, there is plenty of scope for this chemistry to evolve as one of the most explored areas of research in the coming years. Therefore, a highlight article about alkynes is both timely and useful for synthetic chemists working in this area. Herein, we have highlighted the diverse reactivity of alkynes with various transition metals (Ir, Rh, Ru, Pd, Mn, Fe, Co, Ni, Cu) and their applications, along with some of our thoughts on future prospects.

Metal-catalyzed reactions of organic nitriles and boronic acids to access diverse functionality

The nitrile or cyano (-CN) group is one of the most appreciated and effective functional groups in organic synthesis, having a polar unsaturated C-N triple bond. Despite sufficient stability and being intrinsically inert, the nitrile group can be easily transformed into many other functional groups, such as amines, carboxylic acids, ketones, etc. which makes it a vital group in organic synthesis. On the other hand, despite several boronic acids having a low level of genotoxicity, they have found wide applicability in the field of organic synthesis, especially in transition metal-catalyzed cross-coupling reactions. Recently, transition-metal-catalyzed cascade additions or addition/cyclization processes of boronic acids to the nitrile group open up exciting and useful strategies to prepare a variety of functional molecules through the formation of C-C, C-N and CO bonds. Boronic acids can be added to the cyano functionality through catalytic carbometallation or through a radical cascade process to provide newer pathways for the rapid construction of various important acyclic ketones or amides, carbamidines, carbocycles and N,O-heterocycles. The present review focuses on various transition-metal-catalyzed additions of boronic acids via carbometallation or radical cascade processes using the cyano group as an acceptor.

Cu(I)/Pd(II)-Catalyzed Intramolecular Hydroamidation and C-H Dehydrogenative Coupling of ortho-Alkynyl-N-arylbenzamides for Access to Isoindolo[2,1-a]Indol-6-Ones

An efficient, atom-economic and one-pot synthesis of isoindolo[2,1-a]indol-6-ones via CuI/Pd(OAc)₂-catalyzed intramolecular hydroamidation of alkynyl group, and C-H dehydrogenative coupling of ortho-alkynyl-N-arylbenzamides has been developed. This transformation occurs with the use of oxygen as the oxidant, and water is the only by-product. The reaction shows a high tolerance to a variety of functional groups, and affords isoindolo[2,1-a]indol-6-ones in good to high yields.

Synthesis of Indole-Fused Six-, Seven-, or Eight-Membered N,O-Heterocycles via Rhodium-Catalyzed NH-Indole-Directed C-H Acetoxylation/Hydrolysis/Annulation

We report herein the facile synthesis of indole-fused six-, seven-, or eight-membered N,O-heterocycles through rhodium-catalyzed C-H acetoxylation/hydrolysis/annulation. The notable features of this method include C-H acetoxylation using NH-indole as the intrinsic directing group, high functional group compatibility, and construction of indole-fused medium-sized rings.

Synthesis of π-Extended Heterocycles via Rh(III)-Catalyzed Oxidative Annulation of 5-Aryl Pyrazinones with Alkynes

The Rh(III)-catalyzed C-H functionalization and subsequent oxidative annulation between 5-aryl pyrazinones and internal alkynes are reported. This protocol provides facile access to a wide range of pyrazinone-linked naphthalenes via the C(sp²)-H alkenylation and subsequent annulation. This transformation is characterized by mild conditions, simplicity, and excellent functional group compatibility. Notably, it is a first report of the utilization of pyrazinones as directing groups in C-H functionalization.

Base-Promoted One-Pot Synthesis of Pyridine Derivatives via Aromatic Alkyne Annulation Using Benzamides as Nitrogen Source

In the presence of Cs₂CO₃, the first simple, efficient, and one-pot procedure for the synthesis of 3,5-diaryl pyridines via a variety of aromatic terminal alkynes with benzamides as the nitrogen source in sulfolane is described. The formation of pyridine derivatives accompanies the outcome of 1,3-diaryl propenes, which are also useful intermediates in organic synthesis. Thus, pyridine ring results from a formal [2+2+1+1] cyclocondensation of three alkynes with benzamides, and one of the alkynes provides one carbon, whilst benzamides provide a nitrogen source only. A new transformation of alkynes as well as new utility of benzamide are found in this work.

Rhodium-Catalyzed Oxidative Annulation of 2- or 7-Arylindoles with Alkenes/Alkynes Using Molecular Oxygen as the Sole Oxidant Enabled by Quaternary Ammonium Salt

Developing an efficient catalytic system using molecular oxygen as the oxidant for rhodium-catalyzed cross-dehydrogenative coupling remains highly desirable. Herein, rhodium-catalyzed oxidative annulation of 2- or 7-phenyl-1H-indoles with alkenes or alkynes to assemble valuable 6H-isoindolo[2,1-a]indoles, pyrrolo[3,2,1-de]phenanthridines, or indolo[2,1-a]isoquinolines using the atmospheric pressure of air as the sole oxidant enabled by quaternary ammonium salt has been accomplished. Mechanistic studies provided evidence for the fast intramolecular aza-Michael reaction and aerobic reoxidation of Rh(I)/Rh(III), facilitated by the addition of quaternary ammonium salt.

Synthesis of 1-Benzyl-, 1-Alkoxyl-, and 1-Aminoisoquinolines via Rhodium(III)-Catalyzed Aryl C-H Activation and Alkyne Annulation

One-pot syntheses of 1-benzyl-, 1-alkoxyl-, and 1-alkylamino- isoquinolines through automatic directing group (DG^auto)-assisted, rhodium(III)-catalyzed aryl C-H activation and annulation with internal alkynes were developed. The reactions affording 1-benzylisoquinolines involve a cascade oximation of diarylacetylenes with hydroxylamine, forming aryl benzyl ketone oxime, and oxime-assisted rhodium(III)-catalyzed aryl C-H activation and followed annulation with another molecule of diarylacetylene in a one-pot manner. The formation of 1-alkoxyl/amino isoquinolines includes the addition of nucleophilic alcohols or amines to aryl nitriles, imine-assisted rhodium-catalyzed aryl C-H activation, and subsequent alkyne annulation.

Biaryl Formation via Base-Promoted Direct Coupling Reactions of Arenes with Aryl Halides

In the absence of ligand, Cs2CO3-promoted cross-coupling reaction of arenes with cyano-/nitro-substituted aryl halides in DMSO affording biaryls is reported. The cyano/nitro group in biaryls is useful and convenient for further transformation. The formation of dibenzofurans resulting from the reactions between arenes and 1-bromo-2-iodobenzene is also reported. On the basis of control experiments and theoretical studies, a radical mechanism is proposed for the formation of biaryls.

Ni-Catalyzed Dual C-H Annulation of Benzimidazoles with Alkynes for Synthesis of π-Extended Heteroarenes

Transition metal catalyzed dual C-H activation and annulation with alkynes was an attractive protocol to construct polycyclic π-extended structures. However, most of them were dominated by noble metal catalysts. Disclosed herein was the study of base-metal Ni-catalysis for dual C-H annulation of N-aromatic imidazole, which produced a range of desired polycyclic aza-quinolines in 48-95% yields. The use of bifunctional phosphine oxide ligand proved to be critical for success.

Rhodium(III)-Catalyzed C-H Bond Functionalization of 2-Pyridones with Alkynes: Switchable Alkenylation, Alkenylation/Directing Group Migration and Rollover Annulation

Cp*Rh(III)-catalyzed chelation-assisted direct C-H bond functionalization of 1-(2-pyridyl)-2-pyridones with internal alkynes that can be controlled to give three different products in good yields has been realized. Depending on the reaction conditions, solvents and additives, the reaction pathway can be switched between alkenylation, alkenylation/directing group migration and rollover annulation. These reaction manifolds allow divergent access to a variety of valuable C6-alkenylated 1-(2-pyridyl)-2-pyridones, (Z)-6-(1,2-diaryl-2-(pyridin-2-yl)vinyl)pyridin-2(1H)-ones and 10H-pyrido[1,2-a][1,8]naphthyridin-10-ones from the same starting materials. These protocols exhibit excellent regio- and stereoselectivity, broad substrate scope, and good tolerance of functional groups. A combination of experimental and computational approaches have been employed to uncover the key mechanistic features of these reactions.

Cobalt-Catalyzed C-H Activation/Annulation of Benzamides with Fluorine-Containing Alkynes: A Route to 3- and 4-Fluoroalkylated Isoquinolinones

The C-H activation/annulation reaction of various benzamides with fluoroalkylated alkynes in the presence of a Co(acac)₂·2H₂O catalyst proceeded very smoothly to give the corresponding 3- and 4-fluoroalkylated isoquinolinones in excellent yields with approximately 70% regioselectivities. These regioisomers could be successfully separated and obtained in pure form. Major or minor regioisomers were determined as 4- or 3-fluoroalkylated isoquinolinones, respectively, based on X-ray crystallographic analyses.

Rhodium(III)-catalyzed oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols

An efficient Rh(iii)-catalyzed C-H oxidative alkylation of N-aryl-7-azaindoles with cyclopropanols by merging tandem C-H and C-C cleavage was developed. This transformation features mild reaction conditions, high regioselectivity, and excellent functional group compatibility. The resulting β-aryl ketone derivatives can be readily transformed into 7-azaindole-containing π-extended polycyclic heteroarenes.

Divergent rhodium-catalyzed electrochemical vinylic C-H annulation of acrylamides with alkynes

α-Pyridones and α-pyrones are ubiquitous structural motifs found in natural products and biologically active small molecules. Here, we report an Rh-catalyzed electrochemical vinylic C-H annulation of acrylamides with alkynes, affording cyclic products in good to excellent yield. Divergent syntheses of α-pyridones and cyclic imidates are accomplished by employing N-phenyl acrylamides and N-tosyl acrylamides as substrates, respectively. Additionally, excellent regioselectivities are achieved when using unsymmetrical alkynes. This electrochemical process is environmentally benign compared to traditional transition metal-catalyzed C-H annulations because it avoids the use of stoichiometric metal oxidants. DFT calculations elucidated the reaction mechanism and origins of substituent-controlled chemoselectivity. The sequential C-H activation and alkyne insertion under rhodium catalysis leads to the seven-membered ring vinyl-rhodium intermediate. This intermediate undergoes either the classic neutral concerted reductive elimination to produce α-pyridones, or the ionic stepwise pathway to produce cyclic imidates.

Formation of diversified spiro-[imidazole-indene] derivatives from 2H-imidazoles: based on versatile propargyl alcohols

Rh(iii)-Catalyzed efficient cascade annulation for the regioselective construction of various spiro-[imidazole-indene] derivatives has been reported by utilizing versatile propargyl alcohols as coupling partners.

Pd(ii)-Catalyzed enantioconvergent twofold C–H annulation to access atropisomeric aldehydes: a platform for diversity-oriented-synthesis

The first Pd(ii)-catalyzed atroposelective dual C–H annulative strategy for diverse synthesis of functionalized axially chiral biaryls was developed.

Synthesis of functionalized diarylbenzofurans via Ru-catalyzed C–H activation and cyclization under air: rapid access to the polycyclic scaffold of diptoindonesin G

A method was developed for rapid assembly of 2,3-diarylbenzofuran-4-carboxylic acids from m-hydroxybenzoic acids and alkynes via Ru-catalyzed C–H alkenylation and cyclization, which was successfully applied for total synthesis of diptoindonesin G.

Chiral Transient Directing Group Strategies in Asymmetric Synthesis

The development of novel methodologies for catalytic enantioselective functionalization reactions enabled by chiral transient directing groups is accompanying in a paradigm shift in the field of asymmetric synthesis. In particular, these highly atom- and step-economic enantioinduction processes commonly proceed either via enantioselective C-H functionalization, or via enantioselective hydroarylation of the pro-chiral substrates generating point, axial or planar chirality. The use of the transient directing group strategy in C-H functionalizations precludes the stoichiometric installations and removal of directing groups and enables efficient, more compatible and economical chemical routes. This minireview highlights asymmetric transition-metal-catalyzed methodologies involving chiral transient directing groups together with the scope, utility and future perspective of the field.

Recent Advances in Construction of Polycyclic Natural Product Scaffolds via One-Pot Reactions Involving Alkyne Annulation

Polycyclic scaffolds are omnipresent in natural products and drugs, and the synthetic strategies and methods toward construction of these scaffolds are of particular importance. Compared to simple cyclic ring systems, polycyclic scaffolds have higher structure complexity and diversity, making them suitable for charting broader chemical space, yet bringing challenges for the syntheses. In this review, we surveyed progress in the past decade on synthetic methods for polycyclic natural product scaffolds, in which the key steps are one-pot reactions involving intermolecular or intramolecular alkyne annulation. Synthetic strategies of selected polycyclic carbocycles and heterocycles with at least three fused, bridged, or spiro rings are discussed with emphasis on the synthetic efficiency and product diversity. Recent examples containing newly developed synthetic concepts or toolkits such as collective and divergent total synthesis, gold catalysis, C–H functionalization, and dearomative cyclization are highlighted. Finally, several “privileged synthetic strategies” for “privileged polycyclic scaffolds” are summarized, with discussion of remained challenges and future perspectives.

Transition Metal-Catalyzed Intermolecular Cascade C-H Activation/Annulation Processes for the Synthesis of Polycycles

Polycycles are abundantly present in numerous advanced chemicals, functional materials, bioactive molecules and natural products. However, the strategies for the synthesis of polycycles are limited to classical reactions and transition metal-catalyzed cross-coupling reactions, requiring pre-functionalized starting materials and lengthy synthetic operations. The emergence of novel approaches shows great promise for the fields of organic/medicinal/materials chemistry. Among them, transition metal-catalyzed C-H activation followed by intermolecular annulation reactions prevail, due to their straightforward manner with high atom- and step-economy, providing rapid, concise and efficient methods for the construction of diverse polycycles. Several strategies have been developed for the synthesis of polycycles, relying on sequential multiple C-H activation/annulation, or combination of C-H activation/annulation and further interaction with a proximal group, or merger of C-H activation with a cycloaddition reaction, or in situ formation of the directing group. These are attractive, efficient, step- and atom-economic methods starting from commercially available materials. This Minireview will provide an introduction to transition metal-catalyzed C-H activation for the synthesis of polycycles, helping researchers to discover indirect connections and reveal hidden opportunities. It will also promote the discovery of novel synthetic strategies relying on C-H activation.

Base-Promoted Annulation of Amidoximes with Alkynes: Simple Access to 2,4-Disubstituted Imidazoles

An efficient construction of imidazole ring by a Cs₂CO₃-promoted annulation of amidoximes with terminal alkynes in DMSO has been developed. This protocol provides a simple synthetic route with high atom-utilization for the synthesis of 2,4-disubstituted imidazoles in good yields under transition-metal-free and ligand-free conditions. Internal alkynes can also undergo the annulation to give 2,4,5-trisubstituted imidazoles.

Isoquinolone Synthesis via Zn(OTf)2-Catalyzed Aerobic Cyclocondensation of 2-(1-Alkynyl)-benzaldehydes with Arylamines

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap commercially available Lewis acid as the catalyst, high atom utilization and easily available starting materials.

The C-H Activation/Bidirecting Group Strategy for Selective Direct Synthesis of Diverse 1,1'-Biisoquinolines

Multidentate ligands are highly important but difficult to access. Herein we disclose an atom- and step-economic synthesis of highly substituted 1,1'-biisoquinolines by a C-H activation/bididirecting group strategy. Through rational design of a bididirecting group to "N-OH + N-OAc", selective unsymmetrical diannulation with two different alkynes in a one-pot reaction has been achieved for the first time to access unsymmetrical biisoquinolines. Moreover, the resultant biisoquinolines show tunable photoluminescence and serve as aggregation-induced emission (AIE) systems.

Enantioselective Twofold C-H Annulation of Formamides and Alkynes without Built-in Chelating Groups

Twofold C-H annulation of readily available formamides and alkynes without built-in chelating groups was achieved. Ni-Al bimetallic catalysis enabled by a bulky BINOL-derived chiral secondary phosphine oxide (SPO) ligand proved to be critical for high reactivity and high selectivity. This reaction uses readily available formamides as starting materials and provides a concise synthetic pathway to a broad range of chiral ferrocenes in 40-98 % yield and 93-99 % ee.

Ligand-Enabled Ni-Al Bimetallic Catalysis for Nonchelated Dual C-H Annulation of Arylformamides and Alkynes

A bifunctional secondary phosphine oxide (SPO) ligand-controlled method was developed for Ni-Al-catalyzed nonchelated dual C-H annulation of arylformamides with alkynes, providing a series of substituted amide-containing heterocycles in ≤97% yield. The SPO-bound bimetallic catalysis proved to be critical to the reaction efficiency.

Bidentate Directing Groups: An Efficient Tool in C-H Bond Functionalization Chemistry for the Expedient Construction of C-C Bonds

During the past decades, synthetic organic chemistry discovered that directing group assisted C-H activation is a key tool for the expedient and siteselective construction of C-C bonds. Among the various directing group strategies, bidentate directing groups are now recognized as one of the most efficient devices for the selective functionalization of certain positions due to fact that its metal center permits fine, tunable, and reversible coordination. The family of bidentate directing groups permit various types of assistance to be achieved, such as N,N-dentate, N,O-dentate, and N,S-dentate auxiliaries, which are categorized based on the coordination site. In this review, we broadly discuss various C-H bond functionalization reactions for the formation of C-C bonds with the aid of bidentate directing groups.

One pot synthesis of pyrrolo[3,2,1-de]phenanthridines from 7-phenylindoles via tandem C–H olefination/aza-Michael addition

An unprecedented one-pot C–H olefination/aza-Michael addition tandem process has been developed for the synthesis of pyrrolo[3,2,1-de]phenanthridines from 7-phenylindoles and alkenes using a [Cp*RhCl₂]₂/AgOAc/Me₄NOAc catalytic system.