Palladium-catalyzed 1,1-aryloxygenation of terminal olefins

Construction of Lactones via Ligand-Enabled Ni-Catalyzed Alkene Hydroxylarylation/Lactonization

Here, we report the preparation of lactones via Ni-catalyzed alkene hydroxylarylation and sequential intramolecular lactonization with O2 as a green oxidant and oxygen source. The bulky 1,3-diketone ligand is crucial by enabling Ni-catalyzed hydroxylarylation of alkenes, providing numerous phthalide and furanone derivatives with high efficiency under mild conditions. The synthetic value of this methodology was further demonstrated by the efficient synthesis of typhaphthalide and a monoamine oxidase B inhibitor.

Palladium-catalyzed 1,1-aminoxylation of 3-butenoic acid with 2-alkynylanilines

Herein, a palladium-catalyzed 1,1-aminoxylation of 3-butenoic acid and 2-alkynylanilines has been developed, achieving the installation of two distinct heteroatom motifs across an olefin skeleton. The strategy features a high step and atom economy and good functional group tolerance, which outlines an efficient approach for simultaneously building up γ-butylactone and indole skeletons. Notably, an external ligand, 2,9-dimethyl-1,10-phenanthroline, has been used to succeed in this protocol to effectively suppress the production of indole byproducts.

Pd(II)-Catalyzed 1,2-Oxyarylation of Alkenes with O-Acylhydroxylamines as the Oxygen Source

O-Acylhydroxylamine has been widely employed as an electrophilic amination reagent in transition-metal-catalyzed C-N coupling reactions, but its use as an electrophilic oxygen source has not been disclosed. Here, we report a Pd-catalyzed 1,2-oxyarylation of alkenes with O-acylhydroxylamines as an oxidant and an oxygen source for the first time. With simple amide as the monodentate directing group, this method features a broad substrate scope, good functional group tolerance, and mild conditions.

Orthogonal Olefination with Organogermanes

Reported herein is a fully orthogonal olefination, which involves the site- and E-selective coupling of aryl germanes with alkenes, tolerating otherwise widely employed coupling handles such as aromatic (pseudo)halogens (C-I, C-Br, C-Cl, C-F, C-OTf, C-OSO2 F), silanes and boronic acid derivatives as well as alternative functionalities. This unprecedented [Ge]-based oxidative Heck coupling proceeds at room temperature with high speed (10 min to 2 hours) and operational simplicity owing to its base-free and air-tolerant features.

Ligand-Enabled NiII -Catalyzed Hydroxylarylation of Alkenes with Molecular Oxygen

The use of molecular oxygen as the terminal oxidant in transition metal catalyzed oxidative process is an appealing and challenging task in organic synthetic chemistry. Here, we report a Ni-catalyzed hydroxylarylation of unactivated alkenes enabled by a β-diketone ligand with high efficiency and excellent regioselectivity employing molecular oxygen as the oxidant and hydroxyl source. This reaction features mild conditions, broad substrate scope and incredible heterocycle compatibility, providing a variety of β-hydroxylamides, γ-hydroxylamides, β-aminoalcohols, γ-aminoalcohols, and 1,3-diols in high yields. The synthetic value of this methodology was demonstrated by the efficient synthesis of two bioactive compounds, (±)-3'-methoxyl citreochlorol and tea catechin metabolites M4.

Pd-Catalyzed 1,3-Alkenylarylation of Skipped Diene via Metal Migration

We disclose a palladium-catalyzed difunctionalization of skipped diene with alkenyl triflates and arylboronic acids to produce 1,3-alkenylarylated products. The reaction proceeded efficiently with Pd(acac)2 as a catalyst and CsF as a base for a wide range of electron-deficient and electron-rich arylboronic acids as well as oxygen-heterocyclic, sterically hindered, and complex natural product-derived alkenyl triflates bearing various functional groups. The reaction produced 3-aryl-5-alkenylcyclohexene derivatives with 1,3-syn-disubstituted stereochemistry.

Palladium-Catalyzed 1,1-Alkynyloxygenation of 2-Vinylbenzoates with Alkynyl Bromides

The palladium-catalyzed reaction of alkyl 2-vinylbenzoates with silyl-protected alkynyl bromides leads to the selective production of 3-alkynylated isochroman-1-ones. The use of an alkyl ester group as an effective oxygen nucleophile is crucial for the efficient 1,1-alkynyloxygenation of alkenes.

Visible-Light-Promoted Catalyst-Free Oxyarylation and Hydroarylation of Alkenes with Carbon Dioxide Radical Anion

Visible-light-mediated oxyarylation and hydroarylation of alkenes with aryl halides using formate salts as the reductant and hydrogen source under ambient conditions were developed. These protocols represent rare catalyst-free examples of the realization of such transformations. Using styrenes as substrates, oxyarylation could occur smoothly. Whereas, hydroarylation proceeds employing electron deficient alkenes. Moreover, dehalogenation proceeds successfully in the absence of alkenes. We expected that this method could provide a valuable strategy for the functionalization of aryl halides.

Palladium-Catalyzed Organic Reactions Involving Hypervalent Iodine Reagents

The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C—H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C—H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.

Controllable access to trifluoromethyl-containing indoles and indolines: Palladium-catalyzed regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides

The synthesis of diverse products from the same starting materials is always attractive in organic chemistry. Here, a palladium-catalyzed substrate-controlled regioselective functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides has been developed, which provides a direct but controllable access to a variety of structurally diverse trifluoromethyl-containing indoles and indolines. In more detail, with respect to γ,δ-alkenes, 1,1-geminal difunctionalization of unactivated alkenes with trifluoroacetimidoyl chloride enables the [4 + 1] annulation to produce indoles; as for β,γ-alkenes, a [3 + 2] heteroannulation with the hydrolysis product of trifluoroacetimidoyl chloride through 1,2-vicinal difunctionalization of alkenes occurs to deliver indoline products. The structure of alkene substrates differentiates the regioselectivity of the reaction.

A palladium-catalyzed dual functionalization of unactivated alkenes with trifluoroacetimidoyl chlorides toward the synthesis of structurally diverse trifluoromethyl-containing indoles and indolines has been developed.

Pd/Xiang-Phos-catalyzed enantioselective intermolecular carboheterofunctionalization of norbornene and norbornadiene

A highly enantioselective Pd/Xiang-Phos-catalyzed carbohetero-functionalization of norbornene is described, giving a direct access to various chiral norbornane-fused dihydrofurans and dihydro-pyrroles. This synthetic methodology provides the first example of asymmetric carboetherification of norbornene, and also tolerates norbornadiene well.

Hypervalent Iodine Reagents in Palladium-Catalyzed Oxidative Cross-Coupling Reactions

Hypervalent iodine compounds are valuable and versatile reagents in synthetic organic chemistry, generating a diverse array of useful organic molecules. Owing to their non-toxic and environmentally friendly features, these reagents find potential applications in various oxidative functionalization reactions. In recent years, the use of hypervalent iodine reagents in palladium-catalyzed transformations has been widely studied as they are strong electrophiles and powerful oxidizing agents. For instance, extensive work has been carried out in the field of C–H bond functionalization via Pd-catalysis using hypervalent iodine reagents as oxidants. In addition, nowadays, iodine(III) reagents have been frequently employed as arylating agents in Pd-catalyzed C–H arylation or Heck-type cross-coupling reactions. In this review, recent advancements in the area of palladium-catalyzed oxidative cross-coupling reactions using hypervalent iodine reagents are summarized in detail.

Walking metals: catalytic difunctionalization of alkenes at nonclassical sites

Migration of metals along a carbon chain is triggered by two of the most common organometallic elementary steps - β-hydride (β-H) elimination and alkene hydrometallation. This process heralds a new future for creating bonds at carbon sites that fall outside the tenets of the conventional wisdom for reactivity and bond formation, and provides an opportunity to leverage β-H elimination to advance the very reaction of alkene difunctionalization it is intrinsically predestined to disrupt. Almost four decades since its genesis, the early adventure for alkene difunctionalization by metal migration was sporadic, and its later development went on a hiatus primarily due to original impetus on arresting β-H elimination for vicinal alkene difunctionalization. With the recent surge on alkene difunctionalization, efforts have been gradually shifting to harnessing the process of β-H elimination to difunctionalize alkenes at sites other than the classical vicinal carbons, termed henceforth nonclassical reaction sites for pedagogical simplicity. In this review article, we extricate and examine the origin and the development of such reactions over the years. This review covers a wide range of reactions for the difunctionalization of alkenes at geminal (1,1), allylic (1,3) and remote (1,n) carbon sites with a variety of coupling partners. These reactions have enabled engineering of complex molecular frameworks with the generation of new carbon-carbon (C-C)/C-C, C-C/C-heteroatom (halogens, O, N, B) and C-B/C-B bonds. The development of these unique transformations is also presented with mechanistic hypotheses and experimental evidences put forward by researchers. Judged by the number of reports emerging recently, it is now strikingly evident that the field of alkene difunctionalization by metal migration has begun to gain momentum, which holds a great future prospect to develop into a synthetic method of enormous potential.

Pd/Xiang-Phos-catalyzed enantioselective intermolecular carboheterofunctionalization under mild conditions

A mild and practical Pd/Xiang-Phos-catalyzed enantioselective intermolecular carboheterofunctionalization reaction of 2,3-dihydrofurans is developed, leading to various optically active fused furoindolines and tetrahydrofurobenzofurans. The key to this transformation is employing two newly modified N-Me-Xiang-Phos ligands ((S, R S)- N-Me-X4/X5) as chiral ligands under mild conditions. Moreover, this synthetic methodology can be efficiently applied to a variety of complex polysubstituted heterocycles with high chemo-, regio-, and enantio-selectivities via introducing diverse substituents on furan rings, which were hard to access by other routes.

Intermolecular oxyarylation of olefins with aryl halides and TEMPOH catalyzed by the phenolate anion under visible light

The phenolate anion was developed as a new photocatalyst with strong reduction potentials (−3.16 V vs. SCE) to reduction of aryl halides to aryl radicals through single electron transfer.

Recent progress of 1,1-difunctionalization of olefins

Olefins are a very important class of compounds and broadly used in the construction of various synthetic building blocks and practical industrial production. The difunctionalization of olefins provides one of the most powerful methods for the C-C or C-X bond formation with a rapid increase of the molecular complexity and synthetic value economically and effectively. Compared with the vigorous growth and abundant achievements of 1,2-difunctionalization of olefins, 1,1-difunctionalization is a relatively emerging and inadequately exploited research direction, despite being tremendously attractive from synthetic perspectives. In this minireview, we provide a brief overview of the advancements of 1,1-difunctionalization of olefins in the past twenty years, and prospects of future developments.

Three-component vicinal-diarylation of alkenes via direct transmetalation of arylboronic acids

Transmetalation-initiated three-component vicinal-diarylation of alkenes.

Herein, we report three-component vicinal-diarylation of non-conjugated alkenes initiated by transmetalation of arylboronic acids, which provides complementary access to β,γ-diaryl carbonyl compounds. We have also screened a large number of chiral ligands for developing an enantioselective version of this reaction and obtained the preliminary results (up to 79 : 21 e.r.). Notably, the methodology developed herein represents the first three component syn-vicinal-dicarbofunctionalization of non-conjugated alkenes involving palladium catalysis.

Mechanistic Investigations of the Pd(0)-Catalyzed Enantioselective 1,1-Diarylation of Benzyl Acrylates

A mechanistic study of the Pd-catalyzed enantioselective 1,1-diarylation of benzyl acrylates that is facilitated by a chiral anion phase transfer (CAPT) process is presented. Kinetic analysis, labeling, competition, and nonlinear effect experiments confirm the hypothesized general mechanism and reveal the role of the phosphate counterion in the CAPT catalysis. The phosphate was found to be involved in the phase transfer step and in the stereoinduction process, as expected, but also in the unproductive reaction that provides the traditional Heck byproduct. Multivariate correlations revealed the CAPT catalyst's structural features, affecting the production of this undesired byproduct, as well as weak interactions responsible for enantioselectivity. Such putative interactions include π-stacking and a CH···O electrostatic attraction between the substrate benzyl moiety and the phosphate. Analysis of the computed density functional theory transition structures for the stereodetermining step of the reaction supports the multivariate model obtained. The presented work provides the first comprehensive study of the combined use of CAPT and transition metal catalysis, setting the foundation for future applications.

Palladium-Catalyzed Enantioselective Intermolecular Carboetherification of Dihydrofurans

A novel enantioselective Pd-catalyzed intermolecular carboetherification of dihydrofurans is reported. The in situ generation of chiral bis-phosphine mono-oxide ligands is crucial, and a general catalytic system has been identified based on this approach. It provides access to a variety of fused tetrahydrofurobenzofurans in consistently high yield and enantiomeric excess.

Palladium-Catalyzed Intermolecular Oxyarylation of Vinylacetates with Retention of an Alkenyl Moiety

Palladium-catalyzed intermolecular oxyarylation reaction of vinylacetates with retention of the double bond in the final product is developed. Under the optimized reaction conditions, the desired products of multisubstituted vinylesters could be obtained in moderate to high yields.

Versatile Enantioselective Synthesis of Functionalized Lactones via Copper-Catalyzed Radical Oxyfunctionalization of Alkenes

A versatile method for the rapid synthesis of diverse enantiomerically enriched lactones has been developed based on Cu-catalyzed enantioselective radical oxyfunctionalization of alkenes. The scope of this strategy encompasses a series of enantioselective difunctionalization reactions: oxyazidation, oxysulfonylation, oxyarylation, diacyloxylation, and oxyalkylation. These reactions provide straightforward access to a wide range of useful chiral lactone building blocks containing tetrasubstituted stereogenic centers, which are hard to access traditionally.

Manganese(IV)-mediated hydroperoxyarylation of alkenes with aryl hydrazines and dioxygen from air

We report a new carbooxygenation-type version of the Meerwein arylation in which the introduction of oxygen is achieved by using dioxygen from the air. In this way, hydroperoxides were obtained from activated as well as non-activated alkenes by oxidizing aryl hydrazines with manganese dioxide. The best results were obtained with α-substituted acrylates. Importantly, the aryl hydrazine has to be added slowly to the reaction mixture to allow sufficient uptake of dioxygen from the air. Competition and labeling experiments revealed hydroperoxyl radicals as novel oxygen-centered radical scavengers.

Reactions of [PhI(pyridine)2]2+ with model Pd and Pt II/IV redox couples

The results of the reactions of the dicationic iodine(III) family of oxidants [PhI(pyridine)2](2+) with model Pd(II) and Pt(II) complexes are described. Depending on the specific reaction pairs, a variety of outcomes are observed. For palladium, Pd(IV) complexes cannot be observed but are implicated in C-C and C-N bond formation for Pd(II) starting materials based on phenylpyridine and 2,2-bipyridine, respectively. Theoretical comparisons with similar processes for -Cl and -OAc rather than pyridine indicate that these provide greater thermodynamic stability, and our results here show that they also give greater kinetic stability (the failure of MP2 methods for these systems is quite dramatic). In contrast, oxidation and delivery of the pyridine ligands gives dicationic Pt(IV) complexes that may be isolated and structurally characterized.

Alkene oxyalkylation enabled by merging rhenium catalysis with hypervalent iodine(III) reagents via decarboxylation

Rhenium-catalyzed oxyalkylation of alkenes is described, where hypervalent iodine(III) reagents derived from widely occurring aliphatic carboxylic acids were used as, for the first time, not only an oxygenation source but also an alkylation source via decarboxylation. The reaction also features a wide substrate scope, totally regiospecific difunctionalization, mild reaction conditions, and ready availability of both substrates. Mechanistic studies revealed a decarboxylation/radical-addition/cation-trapping cascade operating in the reaction.

Copper-catalyzed intramolecular alkene carboetherification: synthesis of fused-ring and bridged-ring tetrahydrofurans

Fused-ring and bridged-ring tetrahydrofuran scaffolds are found in a number of natural products and biologically active compounds. A new copper-catalyzed intramolecular carboetherification of alkenes for the synthesis of bicyclic tetrahydrofurans is reported herein. The reaction involves Cu-catalyzed intramolecular addition of alcohols to unactivated alkenes and subsequent aryl C-H functionalization provides the C-C bond. Mechanistic studies indicate a primary carbon radical intermediate is involved and radical addition to the aryl ring is the likely C-C bond-forming mechanism. Preliminary catalytic enantioselective reactions are promising (up to 75% ee) and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism. Catalytic enantioselective alkene carboetherification reactions are rare and future development of this new method into a highly enantioselective process is promising. During the course of the mechanistic studies a protocol for alkene hydroetherification was also developed.

Aryliodine (III) Diacetates as Substrates for Pd-Ag Catalyzed Arylation of Alkenes

An unprecedented application of aryliodine (III) diacetates as substrates in Pd-Ag catalyzed arylation of alkenes is described. The mechanistic studies revealed that the binary Pd-Ag catalysis leads to the decomposition of aryliodine (III) diacetates to oxygen and aryl iodides followed by arylation of alkenes forming Heck-type products. Under optimized conditions both electron-rich and electron-deficient alkenes undergo arylation in high yields. Advantageously, the reaction proceeds smoothly in water as a solvent and neither organic ligands nor inert atmosphere are required.