Three-Component Ruthenium-Catalyzed Direct Meta-Selective C–H Activation of Arenes: A New Approach to the Alkylarylation of Alkenes

Cu0-Promoted Truce-Smiles Rearrangement for Aryl-Difluoromethylenation of C═C Bonds via a Reductive Radical-Polar Crossover Process

An efficient Cu0-promoted Truce-Smiles rearrangement for the aryl-difluoromethylenation of C═C bonds by the reaction of N-alkyl-N-(arylsulfonyl)methacrylamide and 2-bromodifluoromethyl-1,3-benzodiazole via a reductive radical-polar crossover process under mild reaction conditions is presented. The protocol enables practical access to a variety of single regioisomer α-aryl-β-difluoromethylene amides in good to excellent yields through consecutive difluoromethylenation, radical-polar crossover, 1,4-aryl migration, SO2 extrusion, and N-H bond formation cascade reaction.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Ruthenium(II)-Catalyzed Remote C-H Alkylation of Arenes Using Diverse N-Directing Groups through Aziridine Ring Opening

An efficient approach for the remote C-H alkylation of arenes, employing a variety of N-directing groups is described. This method facilitates the straightforward synthesis of valuable phenylethylamine derivatives by exclusively cleaving the benzylic C-N bond in aziridines. Furthermore, these products can easily remove the protecting groups, resulting in a variety of meta-substituted compounds, such as amines and ketones, which hold significance in synthetic chemistry.

Dative Bonding Activation Enables Precise Functionalization of the Remote B-H Bond of nido-Carborane Clusters

The innovation of synthetic strategies for selective B-H functionalization is a pivotal objective in the realm of boron cluster chemistry. However, the precise, efficient, and rapid functionalization of a B-H bond of carboranes that is distant from the existing functional groups remains intractable owing to the limited approaches for site-selective control from the established methods. Herein, we report a dative bonding activation strategy for the selective functionalization of a nonclassical remote B-H site of nido-carboranes. By leveraging the electronic effects brought by the exopolyhedral B(9)-dative bond, a cross-nucleophile B-H/S-H coupling protocol of the distal B(5)-H bond has been established. The dative bond not only amplifies the subtle reactivity difference among B-H bonds but also significantly changes the reactive sites, further infusing nido-carboranes with additional structural diversity. This reaction paradigm features mild conditions, rapid conversion, efficient production, broad scope, and excellent group tolerance, thus enabling the applicability to an array of complex bioactive molecules. The efficient and scalable reaction platform is amenable to the modular construction of photofunctional molecules and boron delivery agents for boron neutron capture therapy. This work not only provides an unprecedented solution for the selective diversification of distal B-H sites in nido-carboranes but also holds the potential for expediting the discovery of novel carborane-based functional molecules.

Highlighting multicomponent reactions as an efficient and facile alternative route in the chemical synthesis of organic-based molecules: a tremendous growth in the past 5 years

Since Strecker's discovery of multicomponent reactions (MCRs) in 1850, the strategy of applying an MCR approach has been in use for over a century. Due to their ability to quickly develop molecular diversity and structural complexity of interest, MCRs are considered an efficient approach in organic synthesis. Although MCRs such as the Ugi, Passerini, Biginelli, and Hantzsch reactions are widely studied, this review emphasizes the significance of selective MCRs to elegantly produce organic compounds of potential use in medicinal chemistry and industrial and material science applications, as well as the use of the MCR approach to sustainable methods. During synthesis, MCRs provide advantages such as atom economy, recyclable catalysts, moderate conditions, preventing waste, and avoiding solvent use. MCRs also reduce the number of sequential multiple reactions to one step.

Intermolecular Regioselective Alkylarylation of Vinylarenes via Photoredox/Nickel Dual Catalysis

A novel photoredox/nickel dual catalytic intermolecular alkylarylation of vinylarenes with tertiary and secondary alkyltrifluoroborates and aryl bromides is described, which affords 1,1-diarylalkane frameworks that are found in various natural products as well as functionalized molecules in good to excellent yield and regioselectivity through a radical relay process. Notably, this redox-neutral reaction could proceed efficiently with good tolerance of various substrates, including a great diversity of commercially available (hetero)aryl bromides, alkyltrifluoroborates, and vinylarenes.

Photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated olefins with aryl bromides

Transition-metal-catalyzed hydroarylation of unactivated alkenes via metal hydride hydrogen atom transfer (MHAT) is an attractive approach for the construction of C(sp2)-C(sp3) bonds. However, this kind of reaction focuses mainly on using reductive hydrosilane as a hydrogen donor. Here, a novel photoinduced Co/Ni-cocatalyzed Markovnikov hydroarylation of unactivated alkenes with aryl bromides using protons as a hydrogen source has been developed. This reaction represents the first example of photoinduced MHAT via a reductive route intercepting an organometallic coreactant. The key to this transformation was that the CoIII-H species was generated from the protonation of the CoI intermediate, and the formed CoIII-C(sp3) intermediate interacted with the organometallic coreactant rather than reacting with nucleophiles, a method which has been well developed in photoinduced Co-catalyzed MHAT reactions. This reaction is characterized by its high catalytic efficiency, construction of quaternary carbons, simple reaction conditions and expansion of the reactive mode of Co-catalyzed MHAT reactions via a reductive route. Moreover, this catalytic system could also be applied to complex substrates derived from glycosides.

Photoredox-Catalyzed Amino-Radical-Transfer-Mediated Three-Component Alkylarylation of Alkenes

We herein reported a novel photoredox-catalyzed three-component alkylarylation of vinyl arenes with alkylboronic pinacol esters (APEs) and cyanoarenes via radical addition/cross-coupling to construct 1,1-diarylalkanes. In this transformation, alkyl radicals were easily available by visible-light-induced oxidative N-H cleavage of morpholine, which used APEs as a radical precursor. Furthermore, this protocol exhibited a broad substrate scope, enabling various styrenes, APEs, and cyanoarenes, as well as bioactive molecule derivatives.

Ligand-enabled ruthenium-catalyzed meta-C-H alkylation of (hetero)aromatic carboxylic acids

Carboxylates are ideal directing groups because they are widely available, readily cleavable and excellent linchpins for diverse follow-up reactions. However, their use in meta-selective C-H functionalizations remains a substantial unmet catalytic challenge. Herein, we report the ruthenium-catalyzed meta-C-H alkylation of aromatic carboxylic acids with various functionalized alkyl halides. A bidentate N-ligand increases the electron density at the metal center of ortho-benzoate ruthenacycles to the extent that single-electron reductions of alkyl halides can take place. The subsequent addition of alkyl radicals is exclusively directed to the position para to the CAr-Ru bond, i.e., meta to the carboxylate group. The resulting catalytic meta-C-H alkylation extends to a wide range of (hetero)aromatic carboxylic acids including benzofused five-membered ring heteroarenes but no pyridine derivatives in combination with secondary/tertiary alkyl halides, including fluorinated derivatives. It also allows site-selective C5-H alkylation of 1-naphthoic acids. The products are shown to be synthetic hubs en route to meta-alkylated aryl ketones, nitriles, amides, esters and other functionalized products.

Photo-Induced Ruthenium-Catalyzed C-H Arylation Polymerization at Ambient Temperature

Transition metal-catalyzed C-H arylation polymerization (CHAP) is an attractive tool for constructing π-conjugated polymers in a sustainable manner. However, the existing methods primarily rely on palladium catalysis, which usually entails harsh reaction conditions and branching/cross-linking. Here we report the first example of an ambient-temperature ruthenium-catalyzed C-H arylation polymerization induced by visible light irradiation. The present polymerization can produce various meta- and para-linked polymers in excellent yields with high molecular weights. The remarkable feature of our mild reaction platform is represented by high chemoselectivity, leading to polymers that are otherwise inaccessible under conventional reaction conditions at high temperatures.

Rhodium-catalyzed three-component C(sp3)/C(sp2)-H activation enabled by a two-fold directing group strategy

Rh-catalyzed three-component C(sp3)/C(sp2)-H activation has been achieved through a two-directing group strategy. This protocol provides a convenient and efficient pathway for the construction of diverse 8-alkyl quinoline derivatives in one-pot. Furthermore, mechanistic studies revealed that the first C-H amidation was significantly faster than the sequential C-H alkylation.

Ruthenium-Catalyzed Difunctionalization of Vinyl Cyclopropanes for Double m-C(sp2)-H/C-5(sp3)-H Functionalization

With in-depth research on 1,2-difunctionalization, remote difunctionalization has garnered widespread attention for achieving multifunctionality. Herein, we report a strategy for achieving remote difunctionalization under mild conditions. This strategy exhibited good substrate suitability and functional group tolerance. In addition, the significance of this method is further evidenced by its successful application in scaling up and conducting additional transformations of target compounds. Mechanistic studies showed that a radical might be involved in this process.

Nickel-Catalyzed Three-Component Unsymmetrical Bis-Allylation of Alkynes with Alkenes: A Density Functional Theory Study

Density functional theory (DFT) characterizations were employed to resolve the structural and energetic aspects and product selectivities along the mechanistic reaction paths of the nickel-catalyzed three-component unsymmetrical bis-allylation of alkynes with alkenes. Our putative mechanism initiated with the in situ generation of the active catalytic species [Ni(0)L2] (L = NHC) from its precursors [Ni(COD)2, NHC·HCl] to activate the alkyne and alkene substrates to form the final skipped trienes. This proceeds via the following five sequential steps: oxidative addition (OA), β-F elimination, ring-opening complexation, C-B cleavage and reductive elimination (RE). Both the OA and RE steps (with respective free energy barriers of 24.2 and 24.8 kcal·mol-1) contribute to the observed reaction rates, with the former being the selectivity-controlling step of the entire chemical transformation. Electrophilic/nucleophilic properties of selected substrates were accurately predicted through dual descriptors (based on Hirshfeld charges), with the chemo- and regio-selectivities being reasonably predicted and explained. Further distortion/interaction and interaction region indicator (IRI) analyses for key stationary points along reaction profiles indicate that the participation of the third component olefin (allylboronate) and tBuOK additive played a crucial role in facilitating the reaction and regenerating the active catalyst, ensuring smooth formation of the skipped triene product under a favorably low dosage of the Ni(COD)2 catalyst (5 mol%).

Visible-Light-Mediated Bimetal-Catalyzed meta-Alkylation of Arenes

A mild approach to the visible-light-mediated bimetal-catalyzed meta-alkylation of arenes has been accomplished. The regioselective meta-alkylation is realized by a bimetallic ruthenium-palladium system. Ruthenium acts as a catalyst for the directing effect and as a photosensitizer, while the cocatalyst palladium behaves as a catalyst for the generation of fluoroalkyl radicals. This reaction not only is suitable for two-component meta-fluoroalkylation of arenes but can also be extended to three-component reactions to achieve bifunctionalization of olefins.

Unlocking regioselective meta-alkylation with epoxides and oxetanes via dynamic kinetic catalyst control

Regioselective arene C-H bond alkylation is a powerful tool in synthetic chemistry, yet subject to many challenges. Herein, we report the meta-C-H bond alkylation of aromatics bearing N-directing groups using (hetero)aromatic epoxides as alkylating agents. This method results in complete regioselectivity on both the arene as well as the epoxide coupling partners, cleaving exclusively the benzylic C-O bond. Oxetanes, which are normally unreactive, also participate as alkylating reagents under the reaction conditions. Our mechanistic studies reveal an unexpected reversible epoxide ring opening process undergoing catalyst-controlled regioselection, as key for the observed high regioselectivities.

Three-Component Direct Phosphorylation of Aldehydes and Alkylation of Ketones: Synthesis of γ-Ketophosphine Oxides under Acidic Conditions

An effective and economical acid-promoted three-component reaction for the construction of C-P and C-C bonds for the synthesis of γ-ketophosphine oxides with water as the only byproduct was developed. Detailed mechanistic experiments confirmed that the reaction proceeds by phospha-aldol elimination, in which a benzylic carbocation is generated from the phosphorylation of aldehydes, which then reacts with ketone enolates under acidic conditions.

The Essence in Selectivity of Copper-Mediated Intermolecular Nucleophilic Substitution of a meta C-H Bond in 2-Methyl-N-methoxyaniline: A Theoretical Study

The detailed mechanism for NHC-Cu(I)-catalyzed intermolecular nucleophilic substitution of the C-H bonds at aniline (2-methyl-N-methoxyaniline) was studied via DFT methods to reveal the essence of the selectivity. Calculations revealed that the meta C-H functionalization proceeds via two nucleophilic attacks on the aromatic ring rather than a one-step meta C-H substitution to give the experimentally observed major product. The reaction is initiated by activation of the substrate via oxidative addition with an NHC-Cu(I) catalyst, through which an umpolung occurs at the ring. From the activated intermediate, methoxyl group transfer to benzyl forms a resting state, while a nucleophile can attack the ortho position of benzyl to form a more stable intermediate. The nucleophile group can then transfer to the meta position by a 1,2-Wagner-Meerwein rearrangement to form the final product through a proton shuttle. In contrast, other transfer processes affording ortho- or para-substituted products encounter higher activation barriers. This work investigates the relationship of product selectivity with the umpolung of the aromatic ring, as well as the priority of a nucleophilic attack at the ortho position of the aromatic, 1,2-Wagner-Meerwein rearrangement from the ortho-substituted intermediate, and proton shuttle from the meta-substituted intermediate.

Iron-Catalyzed para-Selective C-H Allylation of Aniline Derivatives

Transition-metal-catalyzed directed C-H allylation of arenes offers an efficient and straightforward approach to construct value-added allylic arenes. However, these reactions are often performed with precious transition-metal catalysts and mainly limited to ortho-C-H allylation of arenes. Herein, we disclose a novel iron-catalyzed para-C-H allylation of aniline derivatives with allyl alcohols via a chelation-induced strategy, providing various allylic arenes in good yields with excellent regio- and chemoselectivity. A simple FeCl3·6H2O is employed as a catalyst, serving a dual role in the reaction: (1) coordination with N-arylpicolinamide to alter the electronic property of the aromatic ring and (2) reaction with allyl alcohol to form allyl-Fe species.

A Three-Component Arene Difunctionalization: Merger of C(sp3 )/(sp2 )-H Bond Addition

A tandem three-component C-H bond addition involving the activation of an inert C(sp3 )-H bond is reported. The process enables the direct regioselective synthesis of 1,2-difunctionalized arenes with the formation of C(sp3 )- and C(sp2 )-C(arene) bonds. 2-Iodobenzoic acid derivatives behave as masked bifunctional reagent (BFR) and react with 2-pyridyl-methyl sulfoximine (MPyS) protected aliphatic acids bearing α,α-disubstituted groups, and alkenes to produce β-aryl-δ-alkenyl amide derivatives in a single operation. The transformation involves Pd(II)/Pd(IV) and Pd(II)/Pd(0) catalytic systems. Detailed mechanistic studies, including density functional theory (DFT) calculations, reveal the formation of large T-shaped palladacycles and the onset of a 1,2-palladium migration via decarboxylation.

Three-Component Chemo-Selective Synthesis of N-(o-Alkenylaryl) Pyrazoles by Pyrazole Annulation and Rh-Catalyzed Chemo-Selective Aryl C-H Addition Cascade

By using readily available enaminones, aryl hydrazine hydrochlorides, and alkynes as starting materials, the chemo-selective three-component synthesis of atropisomeric N-(o-alkenylaryl) pyrazoles has been efficiently accessed with rhodium catalysis. Unlike Satoh-Miura reaction leading to the alkyne-based C-H benzannulation by using prior prepared N-phenyl pyrazoles and alkynes as substrates, this three-component protocol displays unprecedented selectivity of C-H alkenylation by blocking the second round metal alkenylation with the key protonation step in the presence of acids.

Remote C-H Glycosylation by Ruthenium(II) Catalysis: Modular Assembly of meta-C-Aryl Glycosides

The prevalence of C-aryl glycosides in biologically active natural products and approved drugs has long motivated the development of efficient strategies for their selective synthesis. Cross-couplings have been frequently used, but largely relied on palladium catalyst with prefunctionalized substrates, while ruthenium-catalyzed C-aryl glycoside preparation has thus far proven elusive. Herein, we disclose a versatile ruthenium(II)-catalyzed meta-C-H glycosylation to access meta-C-aryl glycosides from readily available glycosyl halide donors. The robustness of the ruthenium catalysis was reflected by mild reaction conditions, outstanding levels of anomeric selectivity and exclusive meta-site-selectivity.

Palladium-catalyzed difluoroalkylative carbonylation of styrenes toward difluoropentanedioates

The introduction of fluorine atoms into organic molecules is an attractive but challenging topic. In this work, an interesting palladium-catalyzed difluoroalkylative carbonylation of aryl olefins has been developed. A wide range of aryl olefins were transformed into the corresponding difluoropentanedioate compounds with good functional-group tolerance and excellent regioselectivity. Inexpensive ethyl bromodifluoroacetate acts both as a difluoroalkyl precursor and a nucleophile here. Additionally, a scale-up reaction was also performed successfully, and further transformations of the obtained product were shown as well.

Photo-Induced Ruthenium-Catalyzed Double Remote C(sp2 )-H / C(sp3 )-H Functionalizations by Radical Relay

Distal C(sp2 )-H and C(sp3 )-H functionalizations have recently emerged as step-economical tools for molecular synthesis. However, while the C(sp2 )-C(sp3 ) construction is of fundamental importance, its formation through double remote C(sp2 )-H/C(sp3 )-H activation has proven elusive. By merging the ruthenium-catalyzed meta-C(sp2 )-H functionalization with an aliphatic hydrogen atom transfer (HAT) process, we, herein, describe the catalyzed twofold remote C(sp2 )-H/C(sp3 )-H functionalizations via photo-induced ruthenium-mediated radical relay. Thus, meta-C(sp2 )-H arene bonds and remote C(sp3 )-H alkane bonds were activated by a single catalyst in a single operation. This process was accomplished at room temperature by visible light-notably without exogenous photocatalysts. Experimental and computational theory studies uncovered a manifold comprising ortho-C-H activation, single-electron-transfer (SET), 1,n-HAT (n=5-7) and σ-activation by means of a single ruthenium(II) catalyst.

C-H bond activation and sequential addition to two different coupling partners: a versatile approach to molecular complexity

Sequential multicomponent C-H bond addition is a powerful approach for the rapid, modular generation of molecular complexity in a single reaction. In this approach, C-H bonds are typically added across π-bonds or π-bond isosteres, followed by subsequent coupling to another type of functionality, thereby forming two σ-bonds in a single reaction sequence. Many sequential C-H bond addition reactions have been developed to date, including additions across both conjugated and isolated π-systems followed by coupling with reactants such as carbonyl compounds, cyanating reagents, aminating reagents, halogenating reagents, oxygenating reagents, and alkylating reagents. These atom-economical reactions transform ubiquitous C-H bonds under mild conditions to more complex structures with a high level of regiochemical and stereochemical control. Surprising connectivities and diverse mechanisms have been elucidated in the development of these reactions. Given the large number of possible combinations of coupling partners, there are enormous opportunities for the discovery of new sequential C-H bond addition reactions.

Pd(ii)-catalyzed meta-C-H bromination and chlorination of aniline and benzoic acid derivatives

The classic electrophilic bromination leads to ortho- and para-bromination of anilines due to their electron-rich properties. Herein we report the development of an unprecedented Pd-catalyzed meta-C-H bromination of aniline derivatives using commercially available N-bromophthalimide (NBP), which overcomes the competing ortho/para-selectivity of electrophilic bromination of anilines. The addition of acid additives is crucial for the success of this reaction. A broad range of substrates with various substitution patterns can be tolerated in this reaction. Moreover, benzoic acid derivatives bearing complex substitution patterns are also viable with this mild bromination reaction, and meta-C-H chlorination is also feasible under similar reaction conditions. The ease of the directing group removal and subsequent diverse transformations of the brominated products demonstrate the application potential of this method and promise new opportunities for drug discovery.

Stereoselective Synthesis of Allenyl Alcohols by Cobalt(III)-Catalyzed Sequential C-H Bond Addition to 1,3-Enynes and Aldehydes

An efficient and stereoselective CoIII -catalyzed sequential C-H bond addition to 1,3-enynes and aldehydes is disclosed. This transformation represents the first example of sequential C-H bond additions to 1,3-enynes and a second coupling partner and provides the first example of preparing allenes by C-H bond addition to 1,3-enynes. A wide range of aldehydes, C-H bond substrates and 1,3-enynes with large substituents on the alkynes are effective substrates. The allenyl alcohol products can be further converted to dihydrofurans with high stereoselectivity either in situ or under Ag-mediated cyclization conditions. The allenyl silyl group can also be transferred to the adjacent alcohol by a Brook rearrangement. Moreover, a mechanism for the transformation is proposed supported by X-ray structural characterization of a cobaltacycle intermediate.

Ni-Catalyzed Regio- and Stereoselective Alkylarylation of Unactivated Alkenes in γ,δ-Alkenylketimines

We disclose a Ni-catalyzed vicinal alkylarylation of unactivated alkenes in γ,δ-alkenylketimines with aryl halides and alkylzinc reagents. The reaction produces γ-C(sp3)-branched δ-arylketones with the construction of two new C(sp3)-C(sp3) and C(sp3)-C(sp2) bonds. Electron-deficient alkenes play crucial dual roles as ligands to stabilize reaction intermediates and to increase catalytic rates for the formation of C(sp3)-C(sp3) bonds. This alkene alkylarylation reaction is also effective for secondary alkylzinc reagents and internal alkenes, and proceeds with a complete regio- and stereocontrol, affording products with up to three contiguous all-carbon all-cis secondary stereocenters.

Distal Ruthenaelectro-Catalyzed meta-C-H Bromination with Aqueous HBr

While electrochemical ortho-selective C-H activations are well established, distal C-H activations continue to be underdeveloped. In contrast, we herein describe the electrochemical meta-C-H functionalization. The remote C-H bromination was accomplished in an undivided cell by RuCl3 ⋅3 H2 O with aqueous HBr. The electrohalogenation proceeded under exogenous ligand- and electrolyte-free conditions. Notably, pyrazolylarenes were meta-selectively brominated at the benzenoid moiety, rather than on the electron-rich pyrazole ring for the first time. Mechanistic studies were suggestive of an initial ruthenacycle formation, and a subsequent ligand-to-ligand hydrogen transfer (LLHT) process to liberate the brominated product.

meta-Allylation of Arenes via Ruthenium-Catalyzed Cross-Dehydrogenative Coupling

A successful example of oxidative meta-dehydrogenative allylation of arenes with alkenes has been developed using Ru(PPh₃)₃Cl₂ as a catalyst and DTBP as an oxidant. In the allylation process, pyrimidines, pyrazoles, and purines, found widely in nucleosides, were effective auxiliary groups. Gram-scale experiments took place smoothly under optimized conditions. Mechanistic studies indicated that ruthenium-catalyzed meta-dehydrogenative allylation was a free-radical process. The allylation process developed herein provides an efficient and practical strategy to prepare versatile meta-allylated arenes.

Ligand centered redox enabled sustainable synthesis of triazines and pyrimidines using a zinc-stabilized azo-anion radical catalyst

Herein, we report ligand-centered redox controlled Zn(II)-catalyzed multicomponent approaches for synthesizing pyrimidines and triazines. Taking advantage of the ligand-centered redox events and using a well-defined Zn(II)-catalyst (1a) bearing (E)-2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline (L1a) as the redox-active ligand, a wide variety of substituted pyrimidines and triazines were prepared via dehydrogenative alcohol functionalization reactions. Pyrimidines were prepared via two pathways: (i) dehydrogenative coupling of primary and secondary alcohols with amidines and (ii) dehydrogenative coupling of primary alcohols with alkynes and amidines. Triazines were prepared via dehydrogenative coupling of alcohols and amidines. Catalyst 1a is well tolerant to a wide range of substrates yielding the desired pyrimidines and triazines in moderate to good isolated yields. A series of control reactions were performed to predict the plausible mechanism, suggesting that the active participation of the ligand-centered redox events enables the Zn(II)-complex 1a to act as an efficient catalyst for synthesizing these N-heterocycles. Electron transfer processes occur at the azo-aromatic ligand throughout the catalytic reaction, and the Zn(II)-center serves only as a template.

DFT Case Study on the Comparison of Ruthenium-Catalyzed C-H Allylation, C-H Alkenylation, and Hydroarylation

Density functional calculations at the B3LYP-D3+IDSCRF/TZP-DKH(-dfg) level of theory have been performed to understand the mechanism of ruthenium-catalyzed C-H allylation reported in the literature in depth. The plausible pathway consisted of four sequential processes, including C-H activation, migratory insertion, amide extrusion, and recovery of the catalyst, in which C-H activation was identified as the rate-determining step. The amide extrusion step could be promoted kinetically by trifluoroacetic acid since its mediation lowered the free-energy barrier from 32.1 to 12.2 kcal/mol. Additional calculations have been performed to explore other common pathways between arenes and alkenes, such as C-H alkenylation and hydroarylation. A comparison of the amide extrusion and β-H elimination steps established the following reactivity sequence of the leaving groups: protonated amide group > β-H group > unprotonated amide group. The suppression of hydroarylation was attributed to the sluggishness of the Ru-C protonation step as compared to the amide extrusion step. This study can unveil factors favoring the C-H allylation reaction.

Three-Component Ruthenium-Catalyzed meta-C-H Alkylation of Phenol Derivatives

Herein, we realized the multicomponent reactions of phenol derivatives via a six-membered cycloruthenated intermediate for the first time. This strategy exhibited good substrate suitability and functional group tolerance with various phenol derivatives and provided a potential synthetic drug approach. Mechanistic studies showed that a radical might be involved in this process. In addition, the meta alkylated phenol was obtained by further removal of the directing group.

Site-Selective Coupling of Remote C(sp3)−H/meta-C(sp2)−H Bonds Enabled by Ru/Photoredox Dual Catalysis and Mechanistic Studies

Construction of C(sp2)−C(sp3) bonds via regioselective coupling of C(sp2)−H/C(sp3)−H bonds is challenging due to the low reactivity and regioselectivity of C−H bonds. Here, a novel photoinduced Ru/photocatalyst-cocatalyzed regioselective cross-dehydrogenative coupling...

Diversity-Oriented Synthesis of Fluoroalkylated Amines via Palladium-Catalyzed Divergent Fluoroalkylamination of 1,3-Dienes

Herein, we reported the first versatile and expeditious protocol for the diversity-oriented synthesis (DOS) of fluoroalkylated amines via the photoinduced palladium-catalyzed cross coupling of 1,3-dienes, amines and fluoroalkyl iodides, which...

Synthesis of α-Branched Amines by Three- and Four-Component C-H Functionalization Employing a Readily Diversifiable Hydrazone Directing Group

Efficient syntheses of α-branched amines by three- and four-component C-H functionalization employing a diversifiable hydrazone directing group have been developed. The hydrazone in the α-branched amine products has been readily converted to multiple desirable functionalities such as a nitrile, a carboxylic acid, alkenes, and heterocycles using diverse heterolytic chemistry and homolytic transition metal- or photoredox-catalyzed processes. This study represents the first example of a four-component C-H functionalization reaction.

Copper and Photocatalytic Radical Relay Enabling Fluoroalkylphosphorothiolation of Alkenes: Modular Synthesis of Fluorine-Containing S-Alkyl Phosphorothioates and Phosphorodithioates

A photoredox and copper-catalyzed fluoroalkylphosphorothiolation of activated and unactivated alkenes via a radical relay mechanism is reported. By employing fluoroalkyl halides as radical precursors and P(O)SH or P(S)SH compounds as coupling partners, a wide range of β-monofluoroalkyl-, -difluoroalkyl-, -trifluoromethyl-, or -perfluoroalkyl-substituted S-alkyl phosphorothioates and phosphorodithioates can be easily constructed under mild conditions with good functional group tolerance. Furthermore, this modular reaction system can be successfully applied to late-stage functionalization of bioactive molecules.