Synthesis of Biaryls via Catalytic Decarboxylative Coupling

Nickel-Catalyzed Decarboxylative Alkenylation of Anhydrides with Vinyl Triflates or Halides

Decarboxylative cross-coupling of aliphatic acid anhydrides with vinyl triflates or halides was accomplished via nickel catalysis. This methodology works well with a broad array of substrates and features abundant functional group tolerance. Notably, our approach addresses the issue of safe and environmental installation of methyl or ethyl group into molecular scaffolds. The method possesses high chemoselectivity toward alkyl groups when aliphatic/aromatic mixed anhydrides are involved. Furthermore, diverse ketones could be modified with our strategy.

Nickel-catalyzed Suzuki-Miyaura cross-couplings of aldehydes

Transition-metal-catalyzed cross-couplings have been extensively used in the pharmaceutical and agrochemical industries for the construction of diverse C-C bonds. Conventional cross-coupling reactions require reactive electrophilic coupling partners, such as organohalides or sulfonates, which are not environmentally friendly and not naturally abundant. Another disadvantage associated with these transformations is the need for an exogenous base to facilitate the key transmetalation step, and this reagent inevitably induces side reactions and limits the substrate scope. Here, we report an unconventional Suzuki-type approach to the synthesis of biaryls, through nickel-catalyzed deformylative cross coupling of aldehydes with organoboron reagents under base-free conditions. The transformation tolerates structurally diverse (hetero)aryl substituents on both coupling partners and shows high reactivity and excellent functional group tolerance. Furthermore, the protocol was carried out on gram scale and successfully applied to the functionalization of complex biologically active molecules. Mechanistic investigations support a catalytic cycle involving the oxidative addition of the nickel into the aldehyde C(acyl)-H bond with subsequent hydride transfer, transmetalation, decarbonylation and reductive elimination processes.

Formation and reactions of the 1, 8-naphthyridine (napy) ligated geminally dimetallated phenyl complexes [(napy)Cu2(Ph)]+, [(napy)Ag2(Ph)]+ and [(napy)CuAg(Ph)]. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2019;25:30-43. [PMID: 30773925 DOI: 10.1177/1469066718795959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Gas-phase ion trap mass spectrometry experiments and density functional theory calculations have been used to examine the routes to the formation of the 1,8-naphthyridine (napy) ligated geminally dimetallated phenyl complexes [(napy)Cu₂(Ph)]⁺, [(napy)Ag₂(Ph)]⁺ and [(napy)CuAg(Ph)]⁺ via extrusion of CO₂ or SO₂ under collision-induced dissociation conditions from their corresponding precursor complexes [(napy)Cu₂(O₂CPh)]⁺, [(napy)Ag₂(O₂CPh)]⁺, [(napy)CuAg(O₂CPh)]⁺ and [(napy)Cu₂(O₂SPh)]⁺, [(napy)Ag₂(O₂SPh)]⁺, [(napy)CuAg(O₂SPh)]⁺. Desulfination was found to be more facile than decarboxylation. Density functional theory calculations reveal that extrusion proceeds via two transition states: TS1 enables isomerization of the O, O-bridged benzoate to its O-bound form; TS2 involves extrusion of CO₂ or SO₂ with the concomitant formation of the organometallic cation and has the highest barrier. Of all the organometallic cations, only [(napy)Cu₂(Ph)]⁺ reacts with water via hydrolysis to give [(napy)Cu₂(OH)]⁺, consistent with density functional theory calculations which show that hydrolysis proceeds via the initial formation of the adduct [(napy)Cu₂(Ph)(H₂O)]⁺ which then proceeds via TS3 in which the coordinated H₂O is deprotonated by the coordinated phenyl anion to give the product complex [(napy)Cu₂(OH)(C₆H₆)]⁺, which then loses benzene.

Electronic Effect-Guided, Palladium-Catalyzed Regioselective B-H Activation and Multistep Diarylation of o-Carboranes with Aryl Iodides

Density functional theory calculations at IDSCRF-B3LYP/DZVP computational level were conducted on palladium-catalyzed regioselective B-H activation and diarylation of o-carboranes with aryl iodides in solution. Computational results indicate that this reaction follows a multistep mechanism and needs to get over several transition states before the final B(4,5)-diarylated o-carborane derivatives are formed. B-H activation, oxidation addition, and successive reduction of the Pd(II) catalyst involving a Pd(II)-Pd(IV)-Pd(II) catalytic cycle has been confirmed, in which AgOAc plays a crucial role. Electron-donating group on the cage carbon of o-carboranes is verified to be beneficial for its B-H activation and diarylation, while steric hindrance between the aryl and o-carboranyl groups retards it. Natural population analysis and Gibbs free energetic results predict consistent regioselectivities with experiments and manifest the pivotal role of electronic effect in controlling regioselective B-H activation of o-carboranes. These results are expected to shed some light on further improvement of experimental conditions and better controlling of regioselectivities.

Electro-Oxidative C-C Alkenylation by Rhodium(III) Catalysis

Electrochemical C-C activations were accomplished by expedient oxidative rhodium(III) catalysis. Thus, oxidative C-C alkenylations proved viable with the aid of electricity, avoiding the use of toxic and/or expensive transition-metal oxidants. The chelation-assisted C-C functionalizations proceeded with ample scope and excellent levels of chemo- and position selectivities within an organometallic C-C activation manifold. Detailed mechanistic studies provided support for a kinetically relevant C-C scission, and a well-defined organometallic rhodium(III) complex was identified as a catalytically competent intermediate. The electrochemical C-C functionalization was devoid of additional electrolytes, could be conducted on a gram scale, and provided position-selective access to densely 1,2,3-substituted arenes, which are not viable by C-H activation.

An efficient approach to access 1,1,2-triarylethanes enabled by the organo-photoredox-catalyzed decarboxylative addition reaction

An efficient approach to access 1,1,2-triarylethanes enabled by organo-photoredox-catalyzed decarboxylative 1,6-conjugate addition of carboxylic acids to p-QMs.

Direct synthesis of 8-acylated quinoline N-oxidesviapalladium-catalyzed selective C–H activation and C(sp2)–C(sp2) cleavage

An efficient method for the synthesis of 8-acylated quinoline N-oxides from the reaction of quinoline N-oxides with α-diketonesviaC–C bond cleavage was developed. A variety of quinoline N-oxides and α-diketones with different groups was well tolerated in this system.

The decarboxylative C–H heteroarylation of azoles catalysed by nickel catalysts to access unsymmetrical biheteroaryls

The direct decarboxylative C–H heteroarylation of azoles with heteroaryl carboxylic acids through nickel catalysts has been developed.

Direct C-3 alkylation of coumarins via decarboxylative coupling with carboxylic acids

A metal-free direct alkylation of coumarins using carboxylic acids in aqueous media with a broad substrate scope is devised.

Palladium-catalyzed salt-free double decarboxylative aryl allylation

We describe a palladium catalyzed salt-free decarboxylative aryl allylation of free benzoic acids with allyl tert-butyl-carbonates.

Decarboxylative Suzuki–Miyaura coupling of (hetero)aromatic carboxylic acids using iodine as the terminal oxidant

A novel methodology for the decarboxylative Suzuki–Miyaura-type coupling of carboxylic acids with arylboronic acids has been developed.

Beyond the traditional roles of Ag in catalysis: the transmetalating ability of organosilver(i) species in Pd-catalysed reactions

The role of silver salts in Pd-catalysed C–C bond forming transformations.

Decarboxylative cascade cyclization of α-keto acids with 2-cyano-3-arylaniline-derived acrylamides

An oxidative decarboxylative cascade cyclization of α-keto acids with 2-cyano-3-arylaniline-derived acrylamides delivering carbonyl-containing pyrido[4,3,2-gh]phenanthridines is presented.

N2H4 as traceless mediator for homo- and cross- aryl coupling

Transition-metal catalyzed couplings of aryl halides or arenes with aryl organometallics, as well as direct reductive coupling of two aryl halides, are the predominant methods to synthesize biaryls. However, stoichiometric amounts of metals are inevitably utilized in these reactions, either in the pre-generation of organometallic reagents or acting as reductant in situ, thus producing quantitative metal waste. Herein, we demonstrate that this longstanding challenge can be overcome with N₂H₄ as a metal surrogate. The fundamental innovation of this strategy is that N₂ and H₂ are generated as side products, which readily escape from the system after the reaction. The success of both homo- and cross-coupling of various aryl electrophiles bearing a wide range of functional groups manifests the powerfulness and versatility of this strategy. Furthermore, both homo- and cross-couplings of a series of alkaloids, amino acids and steroids exemplify application of this protocol in the functionalization of biologically active molecules.

Synthesis of biaryls by coupling strategies is unavoidably accompanied by stoichiometric metal waste. Here, the authors report the homo- and cross-electrophile coupling by using hydrazine as metal surrogate, only liberating N₂ and H₂ as side products.

Base-free nickel-catalysed decarbonylative Suzuki-Miyaura coupling of acid fluorides

The Suzuki-Miyaura cross-coupling of organoboron nucleophiles with aryl halide electrophiles is one of the most widely used carbon-carbon bond-forming reactions in organic and medicinal chemistry^1,2. A key challenge associated with these transformations is that they generally require the addition of an exogenous base, the role of which is to enable transmetallation between the organoboron nucleophile and the metal catalyst³. This requirement limits the substrate scope of the reaction because the added base promotes competitive decomposition of many organoboron substrates^3-5. As such, considerable research has focused on strategies for mitigating base-mediated side reactions^6-12. Previous efforts have primarily focused either on designing strategically masked organoboron reagents (to slow base-mediated decomposition)^6-8 or on developing highly active palladium precatalysts (to accelerate cross-coupling relative to base-mediated decomposition pathways)^10-12. An attractive alternative approach involves identifying combinations of catalyst and electrophile that enable Suzuki-Miyaura-type reactions to proceed without an exogenous base^12-14. Here we use this approach to develop a nickel-catalysed coupling of aryl boronic acids with acid fluorides^15-17, which are formed in situ from readily available carboxylic acids^18-22. This combination of catalyst and electrophile enables a mechanistic manifold in which a 'transmetallation-active' aryl nickel fluoride intermediate is generated directly in the catalytic cycle^13,16. As such, this transformation does not require an exogenous base and is applicable to a wide range of base-sensitive boronic acids and biologically active carboxylic acids.

Merging base-promoted C-C bond cleavage and iron-catalyzed skeletal rearrangement involving C-C/C-H bond activation: synthesis of highly functionalized carbazoles

An efficient and atom-economical methodology for the synthesis of multi-substituted carbazoles starting from α-aryl ketones and ynones under mild reaction conditions has been developed. This process goes through Cs2CO3 promoted C-C σ-bond activation of α-aryl ketones followed by highly selective C-H bond activations and C-C bond fragmentations in a one-pot operation.

Mechanistic Interrogation of Co/Ni-Dual Catalyzed Hydroarylation

Cobalt/nickel-dual catalyzed hydroarylation of terminal olefins with iodoarenes builds complexity from readily available starting materials, with a high preference for the Markovnikov (branched) product. Here, we advance a mechanistic model of this reaction through the use of reaction progress kinetic analysis (RPKA), radical clock experiments, and stoichiometric studies. Through exclusion of competing hypotheses, we conclude that the reaction proceeds through an unprecedented alkylcobalt to nickel direct transmetalation. Demonstration of catalytic alkene prefunctionalization, via spectroscopic observation of an organocobalt species, distinguishes this Csp2-Csp3 cross-coupling method from a conventional transmetalation process, which employs a stoichiometric organometallic nucleophile, and from a bimetallic oxidative addition of an organohalide across nickel, described by radical scission and subsequent alkyl radical capture at a second nickel center. A refined understanding of the reaction leads to an optimized hydroarylation procedure that excludes exogenous oxidant, demonstrating that the transmetalation is net redox neutral. Catalytic alkene prefunctionalization by cobalt and engagement with nickel catalytic cycles through direct transmetalation provides a new platform to merge these two rich areas of chemistry in preparatively useful ways.

Palladium-Catalyzed Decarboxylative Carbonylative Transformation of Benzyl Aryl Carbonates: Direct Synthesis of Aryl 2-Arylacetates

A procedure on palladium-catalyzed decarboxylative alkoxycarbonylation of carbonates for the synthesis of aryl 2-arylacetates has been developed. A broad range of aryl 2-arylacetates were obtained in good yields under mild conditions under a carbon monoxide atmosphere. Interestingly, other alcohols can be added as nucleophiles as well, and the corresponding esters were also obtained in good yields.