Selective Coupling Reaction Research Articles

Stereoselective C-B and C-H Bonds Functionalization of PolyBorylated Alkenes.

Alkenes are fundamental functional groups which feature in various materials and bioactive molecules; however, efficient divergent strategies for their stereodefined synthesis are difficult. In this regard, numerous synthetic methodologies have been developed to construct carbon-carbon bonds with regio- and stereoselectivity, enabling the predictable and efficient synthesis of stereodefined alkenes. In fact, an appealing alternative approach for accessing challenging stereodefined alkene molecular frameworks could involve the sequential selective activation and cross-coupling of strong bonds instead of conventional C-C bond formation. In this study, we introduce a series of programmed site- and stereoselective strategies that capitalizes on the versatile reactivity of readily accessible polymetalloid alkenes (i.e. polyborylated alkenes), through a tandem cross-coupling reaction, which is catalyzed by an organometallic Rh-complex to produce complex molecular scaffolds. By merging selective C-B and remote C-H bond functionalization, we achieve the in situ generation of polyfunctional C(sp2)-nucleophilic intermediates. These species can be further modified by selective coupling reactions with various C-based electrophiles, enabling the formation of C(sp2)-C(sp3) bond for the generation of even more complex molecular architectures using the readily available starting polyborylated-alkenes. Mechanistic and computational studies provide insight into the origins of the stereoselectivities and C-H activation via a 1,4-Rh migration process.

Stereoselective C−B and C−H Bonds Functionalization of PolyBorylated Alkenes

AbstractAlkenes are fundamental functional groups which feature in various materials and bioactive molecules; however, efficient divergent strategies for their stereodefined synthesis are difficult. In this regard, numerous synthetic methodologies have been developed to construct carbon–carbon bonds with regio‐ and stereoselectivity, enabling the predictable and efficient synthesis of stereodefined alkenes. In fact, an appealing alternative approach for accessing challenging stereodefined alkene molecular frameworks could involve the sequential selective activation and cross‐coupling of strong bonds instead of conventional C−C bond formation. In this study, we introduce a series of programmed site‐ and stereoselective strategies that capitalizes on the versatile reactivity of readily accessible polymetalloid alkenes (i.e. polyborylated alkenes), through a tandem cross‐coupling reaction, which is catalyzed by an organometallic Rh‐complex to produce complex molecular scaffolds. By merging selective C−B and remote C−H bond functionalization, we achieve the in situ generation of polyfunctional C(sp2)‐nucleophilic intermediates. These species can be further modified by selective coupling reactions with various C‐based electrophiles, enabling the formation of C(sp2)−C(sp3) bond for the generation of even more complex molecular architectures using the readily available starting polyborylated‐alkenes. Mechanistic and computational studies provide insight into the origins of the stereoselectivities and C−H activation via a 1,4‐Rh migration process.

Harnessing the potential of acyl triazoles in bifunctional cobalt-catalyzed radical cross-coupling reactions

Persistent radicals facilitate numerous selective radical coupling reactions. Here, we have identified acyl triazole as a new and versatile moiety for generating persistent radical intermediates through single-electron transfer processes. The efficient generation of these persistent radicals is facilitated by the formation of substrate-coordinated cobalt complexes, which subsequently engage in radical cross-coupling reactions. Remarkably, triazole-coordinated cobalt complexes exhibit metal-hydride hydrogen atom transfer (MHAT) capabilities with alkenes, enabling the efficient synthesis of diverse ketone products without the need for external ligands. By leveraging the persistent radical effect, this catalytic approach also allows for the development of other radical cross-coupling reactions with two representative radical precursors. The discovery of acyl triazoles as effective substrates for generating persistent radicals and as ligands for cobalt catalysis, combined with the bifunctional nature of the cobalt catalytic system, opens up new avenues for the design and development of efficient and sustainable organic transformations.

Polyoxometalate‐Based Frameworks: Construction Strategies and Photocatalytic Applications

AbstractPolyoxometalate‐based frameworks, as a kind of material constructed by polyoxometalates (POMs), metal ions or clusters, organic ligands, are combined both the advantages of oxygen‐rich POMs and porous metal‐organic frameworks (MOFs) within one single system. This integration greatly expands their potential applications compared to the individual POMs or MOFs. Particularly for photocatalysis, the narrow light absorption range of the typical POMs units in the ultraviolet region hinders their extensive uses as visible‐light‐driven photocatalysts. However, the incorporation of photoactive units into POMs‐based frameworks can be considered as an effective approach to overcome this limitation. In this paper, we review selected examples of recent progress based on the POM‐based frameworks along with their construction strategies and applications in various areas of photocatalysis, mainly including water splitting, CO2 reduction, organic synthesis and also the selective coupling reactions.

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods.

CeO2 nanorod based catalysts for the base-free synthesis of azoxy-aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (Ov ) and base sites are critical for their excellent catalytic properties. The Ov , i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α-Csp3 -H in ethanol to the nitro group coupling it to the redox reactions between Ce3+ and Ce4+ . At the same time, the base sites catalyze the condensation step to selectively produce azoxy-aromatics. The catalytic route opens a much improved way to use non-noble metal oxides without additives for the selective functional group reduction and coupling reactions.

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods

AbstractCeO2 nanorod based catalysts for the base‐free synthesis of azoxy‐aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (Ov) and base sites are critical for their excellent catalytic properties. The Ov, i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α−Csp3−H in ethanol to the nitro group coupling it to the redox reactions between Ce3+ and Ce4+. At the same time, the base sites catalyze the condensation step to selectively produce azoxy‐aromatics. The catalytic route opens a much improved way to use non‐noble metal oxides without additives for the selective functional group reduction and coupling reactions.

A photoelectrocatalytic system as a reaction platform for selective radical-radical coupling.

The selection of electrode material is a critical factor that determines the selectivity of electrochemical organic reactions. However, the fundamental principles governing this relationship are still largely unexplored. Herein, we demonstrate a photoelectrocatalytic (PEC) system as a promising reaction platform for the selective radical-radical coupling reaction owing to the inherent charge-transfer properties of photoelectrocatalysis. As a model reaction, the radical trifluoromethylation of arenes is shown on hematite photoanodes without employing molecular catalysts. The PEC platform exhibited superior mono- to bis-trifluoromethylated product selectivity compared to conventional electrochemical methods utilizing conducting anodes. Electrochemical and density functional theory (DFT) computational studies revealed that controlling the kinetics of anodic oxidation of aromatic substrates is essential for increasing reaction selectivity. Only the PEC configuration could generate sufficiently high-energy charge carriers with controlled kinetics due to the generation of photovoltage and charge-carrier recombination, which are characteristic features of semiconductor photoelectrodes. This study opens a novel approach towards selective electrochemical organic reactions through understanding the intrinsic physicochemical properties of semiconducting materials.

Selective vapor-phase formation of dimethylformamide via oxidative coupling of methanol and dimethylamine over bimetallic catalysts

Selective dimethylformamide formation occurs over PdAu; reactivity and selectivity are sensitive to Pd : Au ratio. Reaction kinetics suggest a crowded surface and that beneficial effects of surface hydroxyls are induced by co-feeding water.

Structural Optimization of Luminescent Sulfur Dots for Solar Light Induced Efficient and Selective Oxidative Coupling Reactions of Aromatic Amines: A Complete Metal-Free Approach

Structural Optimization of Luminescent Sulfur Dots for Solar Light Induced Efficient and Selective Oxidative Coupling Reactions of Aromatic Amines: A Complete Metal-Free Approach

Nickel-Catalyzed C-I-Selective C(sp2)-C(sp3) Cross-Electrophile Coupling of Bromo(iodo)arenes with Alkyl Bromides.

Despite several methodologies established for C(sp2)-I selective C(sp2)-C(sp3) bond formations, achieving arene-flanked quaternary carbons by cross-coupling of tertiary alkyl precursors with bromo(iodo)arenes in a C(sp2)-I selective manner is rare. Here we report a general Ni-catalyzed C( sp2 )-I selective cross-electrophile coupling (XEC) reaction, in which, beyond 3° alkyl bromides (for constructing arene-flanked quaternary carbons), 2° and 1° alkyl bromides are also demonstrated to be viable coupling partners. Moreover, this mild XEC displays excellent C(sp2)-I selectivity and functional group compatibility. The practicality of this XEC is demonstrated in simplifying the routes to several medicinally relevant and synthetically challenging compounds. Extensive experiments show that the terpyridine-ligated NiI halide can exclusively activate alkyl bromides, forming a NiI-alkyl complex through a Zn reduction. Attendant density functional theory (DFT) calculations reveal two different pathways for the oxidative addition of the NiI-alkyl complex to the C(sp2)-I bond of bromo(iodo)arenes, explaining both the high C(sp2)-I selectivity and generality of our XEC.

Plasmon-Mediated Selective Chemical Reaction of Aromatic Molecules with Amino and Nitro Functional Groups

The plasmon-mediated chemical reaction (PMCR) of aromatic molecules with different functional groups is the frontier topic in the photochemistry area. In this work, two typical Ag-plasmon-catalyzed reactions in aqueous environments are studied, in which the selective reduction reactions of 2-amino-5-nitrobenzenethiol (2A-5NBT) molecules to 3,3′-dimercapto-4,4′-diaminoazobenzene (M1) and the reduction of M1 to 2,5-aminobenzenethiol (M2) by NaBH4 are observed. The mechanism of these two reactions is discussed combined with the calculated Raman spectra. These results demonstrate that 2A-5NBT molecules are selectively catalyzed to M1 in aqueous environments and M1 can be reduced to form M2 in the presence of NaBH4 as a reducing agent. Furthermore, the kinetics of the reduction reaction are analyzed based on surface-enhanced Raman spectroscopy (SERS), which conforms to the first-order kinetic process. This work provides a new perspective on the modulation of selective surface-catalyzed coupling reactions on 2A-5NBT molecules and facilitates the broadening of the research field of in situ monitoring of PMCRs by SERS technology.

Site-Selective Oxidative Coupling Reaction of Diamines toward Aminoazo Compounds

A selective oxidative coupling reaction of a diamine containing both C- and N-NH2 was achieved using acidic potassium permanganate as the coupling reagent. The reaction conditions were optimized, and the reaction selectivity was illustrated by quantum calculations. Furthermore, the azo-coupled product was derivatized to four nitroamine energetic materials with excellent detonation performances.

Regio- and stereoselective divergent cross-coupling of alkynes and disubstituted alkenes via photoredox cobalt dual catalysis

Regio- and stereoselective divergent cross-coupling of alkynes and gem-disubstituted alkenes has been reported by merging visible light photoredox and cobalt catalysis. The selective ene-type or reductive coupling reaction has been achieved by stwich of different ligands.

A theoretical study of selective radical relay and coupling reactions for alkene difunctionalization

The present work developed a radical relay model for cross-coupling reactions involving multi-radical systems.

KOtBu-mediated transition-metal-free synthesis of pyrimidines by selective three-component coupling reactions: A mechanistic insight

A KOtBu-mediated strategy for pyrimidine synthesis via selective three-component coupling reactions has been disclosed. This chemistry, in which a series of pyrimidines (20 examples) can be prepared with moderate to excellent yields, has high potential for large-scale operation owing to its metal-free conditions, atom and step economy. According to mechanistic studies, oxidative species can be generated from KOtBu or toluene in the presence of air, which can initiate the oxidation of alcohols to aldehydes (or ketones). Meanwhile, KOtBu not only promotes the condensation-cyclization process, but also triggers the dehydrogenation of dihydropyrimidine ring.

Synthesis of well-defined linear-bottlebrush-linear triblock copolymer towards architecturally-tunable soft materials.

Linear–bottlebrush–linear (LBBL) triblock copolymers are emerging systems for topologically-tunable elastic materials. In this paper, a new synthetic methodology is presented to synthesize LBBL polystyrene-block-bottlebrushpolydimethylsiloxane-block-polystyrene (PS-b-bbPDMS-b-PS) triblock copolymer via the “grafting onto” approach where the precursors are individually synthesized through living anionic polymerization and selective coupling reaction. In this two-step approach, polystyrene-block-polymethylvinylsiloxane (PS-b-PMVS) diblock copolymer with a low dispersity couples with another living PS block to form PS-b-PMVS-b-PS triblock copolymer. Secondly, this is followed by grafting of separately prepared monohydride-terminated PDMS chains with controllable grafting density through a hydrosilylation reaction. In addition to fully tunable architectural parameters, this approach permits a quantitative determination of the ratio of diblock and triblock bottlebrush copolymers and consistency between batches, highlighting the feasibility for scaled-up production. These LBBL triblock copolymers self-assemble into soft, low-modulus thermoplastic elastomers, and the precise knowledge of the composition is crucial for correlating microstructure to mechanical properties.

Divergent oxidative dearomatization coupling reactions to construct polycyclic cyclohexadienones.

Highly selective divergent oxidative dearomatization coupling reactions, in which the chemoselectivity is controlled by catalysts and bases, are reported herein. Three different kinds of polycyclic cyclohexadienones are produced from the same reactants (41 examples, 85-99% yield). Our method marks a novel copper- and palladium-catalyzed C-H oxidative dearomatization of phenolic derivatives.

A relay catalysis strategy for enantioselective nickel-catalyzed migratory hydroarylation forming chiral α-aryl alkylboronates

A relay catalysis strategy for enantioselective nickel-catalyzed migratory hydroarylation forming chiral α-aryl alkylboronates

Co-Crystal Formation of Partially Fluorinated 1,3,5-Tris(phenylethynyl)benzenes.

Several rigid 1,3,5‐tris(phenylethynyl)benzenes with different fluorination patterns were synthesized through selective Sonogashira‐Hagihara coupling reactions to analyze the packing behavior in solid‐state structures. The aggregation is dominated by various intermolecular interactions between aryl substituents, triple bonds, C−H bonds and H⋅⋅⋅F contacts. Co‐crystallization experiments for the analysis of preferred aryl‐aryl‐interactions led to 1 : 1 complexes. Intermolecular phenyl‐perfluorophenyl interactions with short centroid‐centroid distances are dominating these co‐crystal structures. They lead to melting point increases of up to 49 °C for the co‐crystals compared to the pure substances.

Biowaste-derived hydrochar microspheres: Realizing metal-free visible-light photocatalytic oxidation of amines

Metal-free carbon photocatalysts hold great promise in future visible-light-driven selective photocatalytic organic synthesis. However, designing ideal carbon photocatalysts from sustainable strategies to further improve the photo-efficiency and economic nature is crucial for portable industrial applications. Herein, a clean and economic strategy to fabricate hydrochar microspheres as the first metal-free biochar potocatalysts is reported by a facile hydrothermal post-treatment approach from biowaste. The obtained hydrochars present excellent photocatalytic activity and reusability toward the selective oxidative coupling reactions of various amines under visible-light irradiation. Experimental studies and theoretical calculation revealed that the abundant oxygenated functional groups built-in on the surface could function as photocatalytic active sites. In particular, the diphenolic hydroxyl functional groups and quinone moieties attached to the large π-electronic-system were the main active sites involved in the photocatalytic activity. This research highlights that the utilization of sustainable biowaste-derived hydrochar materials as a low-cost and eco-environmental carbocatalysts, may open up a new avenue for light-driven diverse organic transformations.