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

Difunctionalization of bicyclo[1.1.0]butanes enabled by merging C-C cleavage and ruthenium-catalysed remote C-H activation

The high fraction of sp 3-hybridized carbon atom (Fsp 3) character of cyclobutane derivatives renders them as highly promising bioisosteres for otherwise typically flat arenes. Here, to address the current needs in medicinal chemistry for Fsp 3-rich molecules, we disclose a distinct strategy that exploits the merger of C-C scission in bicyclo[1.1.0]butanes (BCBs) with ruthenium-catalysed remote C-H functionalization of heteroarenes, affording densely substituted cyclobutanes in a chemo-controlled manner. This approach enabled the rapid and efficient synthesis of versatile tri- and tetrasubstituted cyclobutanes by coupling a wide range of mono- or disubstituted BCBs with heteroarenes and alkyl halides under mild reaction conditions, featuring ample substrate scope. The C-C/C-H functionalization was ensured by a multifunctional ruthenium(II) catalyst that enabled ruthenacycle-mediated halogen-atom transfer (Ru-XAT), as well as the selective functionalization of BCBs by strain release. Experimental and computational mechanistic studies unravelled a multi-catalysis manifold, while the C-H/C-C functionalization strategy allowed for telescoping late-stage modification.

Ruthenium-Catalyzed Remote Trifunctionalization of Non-Activated Alkenes via Cyano Migration and meta-C(sp2)-H Functionalization

A novel Ru-catalyzed radical-triggered trifunctionalization of hexenenitriles is presented, employing a strategy of remote cyano group migration and meta-C(sp2)-H functionalization. Through remote cyano migration, the alkenyl moiety undergoes difunctionalization to the formation of a benzylic radical intermediate. This intermediate facilitates para-selective C-H bond addition relative to the C-Ru bond within the Ru(III) complex, ultimately enabling trifunctionalization. This methodology provides an efficient route to a diverse array of nitrile-containing compounds with broad functional group compatibility.

Photocatalytic regioselective C-H bond functionalizations in arenes

The direct functionalization of C-H bonds has revolutionized the field of synthetic organic chemistry by enabling efficient and atom-economical modification of arenes by avoiding prefunctionalization. However, the inherent challenges of inertness and regioselectivity in different C-H bonds, particularly for distal positions, necessitate innovative approaches. In this aspect, photoredox catalysis by utilizing both transition metal and organic photocatalysts has emerged as a powerful tool for addressing these challenges under mild reaction conditions. This review provides a comprehensive overview of recent progress in regioselective C-H functionalization in arenes via photocatalysis. Emphasizing the strategies for achieving ortho-, meta-, and para-selectivity, we explore the mechanistic insights, catalyst designs, and the novel methodologies that have expanded the scope of C-H bond functionalization. This discussion aims to offer valuable perspectives for advancing the field and developing more efficient and sustainable synthetic methodologies.

Biomimetic Catalytic Remote Desaturation of Aliphatic Alcohols

Herein we present photoinduced cobaloxime-catalyzed selective remote desaturation of aliphatic alcohols. This transformation, which proceeds efficiently at room temperature, facilitates the synthesis of valuable cyclic and acyclic allylic and homoallylic alcohols from readily available saturated aliphatic alcohols. Remarkably, this method obviates the need for external oxidants, noble metal catalysts, and phosphine ligands.

Rapid and scalable ruthenium catalyzed meta-C-H alkylation enabled by resonant acoustic mixing

Synthetic chemistry approaches for direct C-H bond alkylation offers a promising alternative to traditional functional-group-centered strategies which often involve multi-step procedures and may suffer from a variety of challenges including scalability. Here, we introduce resonant mixing as an efficient method for meta-C-H alkylation of arenes using a Ru-catalyst, avoiding the need for bulk solvents, external temperature, or light. The described methodology is highly rapid, enabling multigram-scale synthesis of meta-alkylation products within a short reaction time and achieving a very high turnover frequency. The reaction operates via a radical mechanism and is characterized by its mild reaction conditions, substrate compatibility, and exceptional meta-selectivity, all while significantly reducing reaction times.

Photoinduced Vitamin-B12-Catalyzed meta-C-H Bromination/Chlorination of Phenol Derivatives Assisted by a U-Shaped Nitrile Template

A photoinduced vitamin-B12-catalyzed meta-C-H bromination/chlorination of phenol derivatives was established using a nitrile directing template and N-bromosuccinimide (NBS)/N-chlorosuccinimide (NCS) as halogenated reagents, and a series of meta-bromination/chlorination products were obtained in yields of 51 to 80%. This strategy overcame the selectivity problem of phenols, which have difficulty obtaining meta-products through conventional electrophilic reactions. Furthermore, natural product resveratrol and an intermediate of the γ-secretase inhibitor were successfully synthesized, which demonstrates the practicability of this method.

Visible light-induced ruthenium(ii)-catalyzed hydroarylation of unactivated olefins

Hydroarylation reactions have emerged as a valuable tool for the direct functionalization of C-H bonds with ideal atom economy. However, common catalytic variants for these transformations largely require harsh reaction conditions, which often translate into reduced selectivites. In contrast, we herein report on a photo-induced hydroarylation of unactivated olefins at room temperature employing a readily available ruthenium(ii) catalyst. Our findings include high position- and regio-selectivity and remarkable tolerance of a wide range of functional groups, which further enabled the late-stage diversification.

A high-efficiency and durable flame retardant for cotton fabrics: Ammonium ethyl acryloylphosphoramidate

The ammonium ethyl acryloylphosphoramidate (AEA) was synthesized by acrylamide, ethanolamine, and phosphorus oxychloride; the nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) were applied to analyze the structure of AEA molecule. Using the dip-cure process to treat raw cotton (RC) with AEA flame retardant, the finished fabric had excellent flame retardancy. The cone calorimeter, thermogravimetric, FTIR, and vertical flame tests illustrated finished fabrics underwent synergistic and condensed-phase flame retardation. The finished fabric also had excellent durability, and the higher the sealing degree of phosphorus atoms, the higher the durability. The limiting oxygen index (LOI) of RC-AEA3-20 (raw cotton finished with 20 wt% AEA3) reached 45.4 %. However, the LOI only dropped to 34.9 % after 50 laundering cycles under the AATCC 61-2013 3 A standard. The excellent durability and FTIR analyses of finished fabrics suggested that the -N-P(=O)-O-C- covalent bond was formed between flame retardant and cellulose. This covalent bond exhibited a p-π conjugation effect, enhancing the stability of -N-P(=O)-O-C- bond, improving the durability of finished fabrics. In conclusion, adding reactive groups into flame retardants, like CH2=CH- and -N-P(=O)-O-NH4+, could increase the durability of finished cotton fabrics.

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.

meta-C-H functionalization of phenylethyl and benzylic alcohol derivatives via Pd/NBE relay catalysis

The transition metal-catalyzed meta-C-H functionalization of alcohols and their hydroxylamine derivatives remains underdeveloped. Herein, we report an efficient meta-C-H arylation of both phenylethyl and benzylic alcohols and their hydroxylamine derivatives using a readily removable oxime ether directing group. Using electronically activated 2-carbomethoxynorbornene as the transient mediator and 3-trifluoromethyl-2-pyridone as the enabling ligand, this reaction features a broad substrate scope and good functional group tolerance. More importantly, with this oxime-directed meta-C-H functionalization, this method provides a dual approach for efficient access to both meta-substituted alcohols and hydroxylamines using two sets of simple deprotection conditions. This protocol leads to the efficient synthesis of bioactive compounds possessing promising reactivities for the treatment of pulmonary fibrosis.

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.

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.

Radical Addition-Enabled C-C σ-Bond Cleavage/Reconstruction to Access Functional Indanones: Total Synthesis of Carexane L

C-C σ-bond cleavage and reconstruction is a significant tool for structural modification in synthetic chemistry but it remains a formidable challenge to perform on unstrained skeletons. Herein, we describe a radical addition-enabled C-C σ-bond cleavage/reconstruction reaction of unstrained allyl ketones to access various functional indanones bearing a benzylic quaternary center. The synthetic utility of this method has been showcased by the first total synthesis of carexane L, an indanone-based natural product.

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.

Merging Visible Light Photocatalysis and P(III)-Directed C-H Activation by a Single Catalyst: Modular Assembly of P-Alkyne Hybrid Ligands

Metal-catalyzed C-H activation strategies provide an efficient approach for synthesis by minimizing atom, step, and redox economy. Developing milder, greener, and more effective protocols for these strategies is always highly desirable to the scientific community. In this study, the utilization of a single rhodium complex enabled the visible-light-induced late-stage C-H activation of biaryl-type phosphines with alkynyl bromides, employing inherent phosphorus atoms as directing groups. This chemistry combines P(III)-directed C-H activation with visible light photocatalysis, under exogenous photosensitizer-free conditions, offering a unique platform for ligand design and preparation. Furthermore, this study also explores the asymmetric catalysis and coordination chemistry of the resulting P-alkyne hybrid ligands with specific transition metals. Experimental results and density functional theory calculations demonstrate the mechanistic intricacies of this transformation.

C-H Bond Activation Relay (CHAR) of Proline Ester Derivatives Promoted by In Situ Triarylamine Radical Cation: Selective Synthesis of 4-Bromopyrrole Derivatives

Using the in situ generated triarylamine radical cation as an initiator, the sp³ C-H bond of proline esters was smoothly oxidized and brominated through C-H activation relay (CHAR), giving a series of 4-bromopyrroles in good yields with high regioselectivity. The mechanistic study revealed that the oxidation of the active C-H bond initiated the followed 1,5-HAT and bromination, which provides a new method to realize the functionalization of the remote C-H bond.

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.

Blue-Light-Induced Iron-Catalyzed α-Alkylation of Ketones

We report a visible-light-induced iron-catalyzed α-alkylation of ketones. The photocatalytic system is based on the single diaminocyclopentadienone iron tricarbonyl complex. Two catalytic intermediates of this complex are able to harvest light, allowing the synthesis of substituted aromatic and aliphatic ketones at room temperature using the borrowing hydrogen strategy in the presence of various substituted primary alcohols as alkylating reagents. Preliminary mechanistic studies unveil the role of light for both the dehydrogenation and reduction step.