Aerobic Oxidative Cross-coupling Research Articles

CuI-Catalyzed Radical Reaction of Benzimidates to Form Valuable 4,5-Dihydrooxazoles through Regioselective Aerobic Oxidative Cross-Coupling.

A straightforward Cu(I)-catalyzed oxidative cross-coupled organic transformation has been developed under mild conditions for the construction of functionalized 4,5-dihydrooxazoles through a four-bond-forming regiocontrolled C-C/C-N/C-O coupling strategy emerging benzimidates, paraformaldehyde, and 1,3-diketo analogues using eco-friendly O2 as the sole oxidant. The fundamental features of these designed approaches involve operational simplicity, selectivity, generality, and a broad substrate scope with high yields under the same reaction conditions.

RecentAdvancesin Aerobic Oxidative ofC-H Bond by Molecular Oxygen Focus on Heterocycles.

Aerobic oxidative cross coupling represents one of the most straightforward and atom-economic methods for construction of C-C and C-X (X = N, O, S, or P) bonds using air as a sustainable external oxidant. The oxidative coupling of C-H bonds in heterocyclic compounds can effectively increase their molecular complexity by introducing new functional groups through C-H bond activation, or by formation of new heterocyclic structures through cascade construction of two or more sequential chemical bonds. This is very useful as it can increase the potential applications of these structures in natural products, pharmaceuticals, agricultural chemicals, and functional materials. This is a representative overview of recent progress since 2010 on green oxidative coupling reactions of C-H bond using O2 or air as internaloxidant focus on Heterocycles. It aims to provide a platform for expanding the scope and utility of air as green oxidant, together with a brief discussion on research into the mechanisms behind it.

Copper-doped carbon nitride as a practical heterogeneous metallaphotocatalyst for aerobic oxidative cross-coupling of tertiary amines with terminal alkynes

A Cu-doped carbon nitride-based heterogeneous metallaphotocatalytic α-alkynylation of tertiary amines has been developed, allowing for green and sustainable synthesis of diverse valuable propargylamines with high efficiency.

Aerobic Oxidative C-H Azolation of Indoles and One-Pot Synthesis of Azolyl Thioindoles by Flavin-Iodine-Coupled Organocatalysis.

The aerobic oxidative cross-coupling of indoles with azoles driven by flavin-iodine-coupled organocatalysis has been developed for the green synthesis of 2-(azol-1-yl)indoles. The coupled organocatalytic system enabled the one-pot three-component synthesis of 2-azolyl-3-thioindoles from indoles, azoles, and thiols in an atom-economical manner by utilizing molecular oxygen as the only sacrificial reagent.

Enantioselective Synthesis of 3,3'-Disubstituted 2-Amino-2'-hydroxy-1,1'-binaphthyls by Copper-Catalyzed Aerobic Oxidative Cross-Coupling.

A challenging direct asymmetric catalytic aerobic oxidative cross-coupling of 2-naphthylamine and 2-naphthol, using a novel CuI /SPDO system, has been successfully developed for the first time. Enantioenriched 3,3'-disubstituted NOBINs were achieved and could be readily derived to divergent chiral ligands and catalysts. This reaction features high enantioselectivities (up to 96 % ee) and good yields (up to 80 %). The DFT calculations suggest that the F-H interactions between CF3 of L17 and H-1,8 of 2-naphthol, and the π-π stacking between the two coupling partners could play vital roles in the enantiocontrol of this cross-coupling reaction.

Rhodium(III)-Catalyzed Aerobic Oxidative C-H Olefination of Unsaturated Acrylamides with Unactivated Olefins.

A rhodium(III)-catalyzed aerobic oxidative cross-coupling of acrylamides with unactivated alkenes via vinylic C-H activation has been developed. The present cross-coupling reaction was examined with a variety of differently functionalized acrylamides and unactivated olefins. In these reactions, highly valuable amide-functionalized butadienes were prepared in good to excellent yields. This protocol was also compatible with Weinreb amides. A possible reaction mechanism involving the chelation-assisted vinylic C-H activation via a carboxylate-assisted deprotonation pathway is proposed.

Formal Aerobic Oxidative Cross-Coupling of Benzofuranones with Azo Compounds Using Pd-μ-hydroxo Complex.

We have developed a catalytic aerobic oxidative dimerization reaction of benzofuranones using a Pd(II)-µ-hydroxo complex. Radical-radical cross-coupling of the resulting dimers with azo compounds enabled the one-pot synthesis of structurally congested benzofuranones having two distinct vicinal all-carbon quaternary centers.

Anthracen-9-ylmethylene-(4-methoxyphenyl)amine: efficient promoter for silver-free palladium-catalyzed aerobic oxidative Sonogashira reactions

An efficient protocol for the synthesis of unsymmetrical substituted diarylacetylenes by the C(sp2)–C(sp) cross-coupling reactions of substituted phenylacetylenes and electronically different arylboronic acids has been developed. Anthracen-9-ylmethylene-(4-methoxyphenyl)amine was employed as an efficient promoter in this Pd(OAc)2-catalyzed oxidative Sonogashira reaction in air in the absence of silver salt under optimized reaction conditions. The impact of reaction parameters such as solvent, base, reaction temperature and time in this silver-free aerobic oxidative Sonogashira cross-coupling reaction was also evaluated. Electron-deficient phenylacetylenes, which are sluggish coupling partners in the traditional Sonogashira reaction, underwent coupling in this protocol. The catalytic system is inexpensive, effortlessly attainable and highly flexible for functionalized phenylacetylenes and arylboronic acids.

Transition-Metal-Free Aerobic Oxidative Cross-Coupling of Indoles with Arylidenemalononitriles

An efficient method for the direct construction of C(sp2)–C(sp2) bonds by aerobic oxidative cross-coupling of indoles with arylidenemalononitriles is described. Various [aryl(1H-indol-3-yl)methylene]malononitriles were efficiently synthesized by using air as an oxidant under mild conditions. The salient features for this protocol are no transition-metal catalysts, no organometallic reagents, high atom economy, high yield, mild conditions, and simple workup procedures.

A Highly Selective Palladium-Catalyzed Aerobic Oxidative Aniline-Aniline Cross-Coupling Reaction.

The first catalytic oxidative aniline-aniline cross-coupling reaction using oxygen as the terminal oxidant is reported. Anilines possessing a pyrrolidino group can be preferentially oxidized under mild aerobic conditions and reacted with other anilines to afford a variety of nonsymmetrical 2-aminobiphenyls with high selectivities. A heterogeneous palladium catalyst is used for the dehydrogenative cross-coupling of anilines with structurally diverse arenes. This reaction does not require stoichiometric oxidants and is an economical and environmentally friendly method.

Aerobic Oxidative Cross-Coupling of Substituted Acrylamides with Alkenes Catalyzed by an Electron-Deficient CpRhIII Complex.

It has been established that an electron-deficient CpRhIII complex, bearing two ester moieties on the Cp ring, [CpERhIII], catalyzes the aerobic oxidative cross coupling of substituted acrylamides with both activated and unactivated alkenes, leading to (2Z,4E)-dienamides, at relatively low temperature (80 °C). Importantly, tertiary, secondary, and primary amide directing groups could equally be used in this catalysis. The mechanistic studies revealed that the electron-deficient nature of the CpERhIII complex facilitates the turnover-limiting vinylic C-H bond cleavage of the acrylamides.

Pd-Catalyzed Aerobic Oxidative Heck Cross-Coupling for the Straightforward Construction of Indole δ-Lactams.

SummaryThe [6.5.6]-tricyclic indole δ-lactam represents a common key intermediate for the synthesis of a broad variety of structurally intriguing indole alkaloids. The development of a method for the versatile and straightforward construction of such structural motif is of great importance for potential synthetic applications. Herein, we present a co-ligand-prompted Pd-catalyzed 6-exo-trig intramolecular cyclization of indolyl amides via the aerobic oxidative Heck cross-coupling. The method provided a general and efficient way for the construction of [6.5.6]-tricyclic indole δ-lactams. A mechanistic study suggests that a Pd(I)/Pd(III) catalytic cycle should be responsible for effective coupling, which represents a mechanistically alternative pathway when compared with the Pd(0)/Pd(II) cycle proposed for other related coupling reactions.

Cobalt(II)[salen]-Catalyzed Selective Aerobic Oxidative Cross-Coupling between Electron-Rich Phenols and 2-Naphthols.

A selectivity-driven catalyst design approach was adopted to address chemoselectivity issues in the oxidative coupling of phenols. This approach was utilized for developing a Co(II)[salen]-catalyzed aerobic oxidative cross-coupling of phenols in a recyclable 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) solvent. The waste-free conditions offer a sustainable entry to nonsymmetric biphenols via a mechanistic scheme that involves coupling of a liberated phenoxyl radical with a ligated 2-naphthoxyl radical.

Investigations of the Copper-Catalyzed Oxidative Cross-Coupling of Tetrahydroisoquinolines with Diethylzinc by a Combination of Mass Spectrometric and Electrochemical Methods.

The aerobic oxidative cross-coupling of tetrahydroisoquinolines (THIQs) with diethylzinc catalyzed by CuCl2 has been examined by means of electrospray mass spectrometry (ESI-MS). Substrates, intermediates, and the product were readily detected. Particular emphasis has been placed on the role of CuCl2 . Formation of the intermediate iminium species has been investigated in more detail by ESI-MS, electrochemistry-coupled ESI mass spectrometry (EC-MS), and cyclic voltammetry (CV). Our experiments have consistently revealed strong influences of the N-substituent of the THIQ derivative and its oxidation stability with respect to CuCl2 . The results may help to expand the synthetic scope of the reaction, while also further establishing EC-MS as a valuable technique for linking mass spectrometry with cyclic voltammetry in mechanistic studies of organic redox reactions.

Visible light-induced aerobic oxidative cross-coupling of glycine derivatives with indoles: a facile access to 3,3′ bisindolylmethanes

A rapid synthesis of 3,3′-bisindolylmethanes is achieved via a photocatalyzed double Friedel–Crafts alkylation reaction between glycine derivatives and indoles.

Visible light-induced aerobic oxidative cross-coupling of glycine esters with α-angelicalactone: a facile pathway to γ-lactams.

A metal-free aerobic oxidative dehydrogenative formal [2 + 3] cyclization of glycine esters with α-angelicalactone has been accomplished via the synergistic combination of photoredox catalysis and acid catalysis. This protocol provides straightforward and facile access to a series of substituted γ-lactams at room temperature under an air atmosphere. Moreover, the reaction could be carried out on a gram scale. The mild conditions as well as the use of cheap substrates and catalyst make this protocol very attractive for further synthetic applications.

Asymmetric Aerobic Oxidative Cross-Coupling of Tetrahydroisoquinolines with Alkynes

An efficient asymmetric aerobic oxidation of tetrahydroisoquinolines with terminal alkynes was realized under mild reaction conditions using O2 as the sole oxidant. A chiral N,N′-dioxide/zinc(II)/iron(II) bimetallic cooperative catalytic system proves to be efficient for the formation of various α-alkynyl substituted tetrahydroisoquinolines in good to excellent yields and enantioselectivities. A primary mechanistic study supports an enantioselective electrophilic addition of zinc acetylide to the iminium intermediates, formed through a molecular O2-involved oxidative process.

A Bioinspired Organocatalytic Cascade for the Selective Oxidation of Amines under Air.

A bioinspired organocatalytic cascade reaction for the selective aerobic oxidative cross-coupling of primary amines to imines is described. This approach takes advantages of commercially available pyrogallol monomeric precursor to deliver low loadings of natural purpurogallin in situ, under air. This is further engaged in a catalytic process with the amine substrate affording, under single turnover, the active biomimetic quinonoid organocatalyst and the homocoupled imine intermediate, which is then converted into cross-coupled imine after dynamic transimination. This organocatalytic cascade inspired by both purpurogallin biosynthesis and copper amine oxidases allows the aerobic oxidation of non-activated primary amines that non-enzymatic organocatalysts were not able to accomplish alone.

K2CO3-promoted aerobic oxidative cross-coupling of trialkyl phosphites with thiophenols

Phosphorylation of thiols has been achievedviaK2CO3-promoted aerobic oxidative cross-coupling of trialkyl phosphites with thiophenols.

ChemInform Abstract: Silver(I)‐Mediated Regioselective Oxidative Cross‐Coupling of Phenol and Aniline Derivatives Resulting in 2′‐Aminobiphenyl‐2‐ols.

Abstract A broad and efficient regioselective aerobic oxidative cross-coupling of phenols and aniline derivatives in the presence of AgNO3 and H2O2 resulting in 2′-aminobiphenyl-2-ols has been developed. This reaction is selective toward the creation of a new C C bond at the ortho position to both amine and hydroxyl functional groups in the respective starting materials. Although oxidative cross-coupling of phenols and anilines resulting in 2′-aminobiphenyl-2-ol derivatives have been reported, these reactions have been mainly limited to 2-naphthol and 1-naphthol. This is one of the rare reports in which this type of cross-coupling reaction is expanded to simple phenol derivatives.