Palladium/Copper‐Catalyzed Oxidative Arylation of Terminal Alkenes with Aroyl Hydrazides

An unprecedented oxidative arylation reaction of terminal alkenes with simple aroyl hydrazides has been developed under aerobic conditions for the stereoselective synthesis of 1,2‐disubstituted alkenes. A range of aroyl hydrazides underwent palladium/copper‐catalyzed oxidative Mizoroki–Heck reaction with terminal alkenes open to air in a 1:1 mixture of dimethyl sulfoxide and acetonitrile to give structurally diverse 1,2‐disubstituted alkenes in moderate to excellent yields with excellent regio‐ and E‐selectivity. The reaction tolerated a wide variety of functional groups, such as alkoxy, hydroxy, amino, fluoro, chloro, bromo, cyano, nitro, ester, amide, imide, phosphine oxide, and sulfone groups, and, moreover, molecular oxygen and dimethyl sulfoxide were demonstrated to serve as terminal oxidants. This study provides a useful method for the stereoselective synthesis of 1,2‐disubstituted alkenes through direct transformation of the vinylic C?H bonds in terminal alkenes.     

Pd(II)-catalyzed dehydrogenative olefination of vinylic C-H bonds with allylic esters: general and selective access to linear 1,3-butadienes

This work demonstrates a general and efficient method to prepare conjugated dienes by Pd(II)-catalyzed direct olefination of unactivated alkenes with allylic esters and acrylates via vinylic C-H activation. Various aryl and heteroaryl alkenes as well as aliphatic alkenes all give the desired linear 1,3-butadienes with retention of the traditional leaving groups such as OAc and other carboxylic acid ester groups.     

Chiral hetero- and carbocyclic compounds from the asymmetric hydrogenation of cyclic alkenes

Several types of chiral hetero- and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P-Ligated iridium catalysts reduced six-membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five-membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five- rather than the six-membered cyclic alkenes. The major enantiomer formed in the reduction of six-membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3-cis-cyclohexane carboxylates.     

Directed Asymmetric Nickel-Catalyzed Reductive 1,2-Diarylation of Electronically Unactivated Alkenes

Transition-metal catalyzed intermolecular 1,2-diarylation of electronically unactivated alkenes has emerged as an extensive research topic in organic synthesis. However, most examples are mainly limited to terminal alkenes. Furthermore, transition-metal catalyzed asymmetric 1,2-diarylation of unactivated alkenes still remains unsolved and is a formidable challenge. Herein, we describe a highly efficient directed nickel-catalyzed reductive 1,2-diarylation of unactivated internal alkenes with high diastereoselectivities. More importantly, our further effort towards enantioselective 1,2-diarylation of the unactivated terminal and challenging internal alkenes is achieved, furnishing various polyarylalkanes featuring benzylic stereocenters in high yields and with good to high enantioselectivities and high diastereoselectivities. Interestingly, the generation of cationic Ni-catalyst by adding alkali metal fluoride is the key to increased efficiency of this enantioselective reaction.     

Intermolecular cycloaddition of N-boranonitrone with alkenes

Ethyl glyoxylate O-tert-butyldimethylsilyloxime (8), on treatment with 2.2 equiv of BF3 x OEt2, generated N-boranonitrone E, which underwent intermolecular cycloaddition with alkenes 18 to afford isoxazolidines 19 in moderate to high yields. The cycloaddition of N-boranonitrone E with most of the alkenes gave 3,5-trans isoxazolidines as the major isomers via a concerted mechanism. However, in the case of 1-methylated cyclic alkenes (18j and 18l), the cycloaddition surprisingly furnished the 3,3a-cis-cycloadducts (19j and 19l) as major isomers. A possible explanation is that the reaction of 1-methylated cyclic alkenes proceeds mainly via a stepwise mechanism. This reaction of terminal alkenes is very useful for synthesis of 1,3-anti aminoalcohol derivatives by reductive cleavage of an N-O bond.     

Metal-Free Electrocatalytic Diacetoxylation of Alkenes

1,2-Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2-dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom-efficient reactant. This transition metal-free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst-free conditions. The synthetic method is extensively investigated with cyclic voltammetry.     

Cobalt-catalyzed efficient aziridination of alkenes

[reaction: see text]. Cobalt porphyrins are capable of catalyzing the aziridination of alkenes with bromamine-T as the nitrene source. Among cobalt complexes of different porphyrins, Co(TDClPP) is an effective catalyst that can aziridinate a wide variety of alkenes. The catalytic system can operate at room temperature in a one-pot fashion with alkenes as limiting reagents, forming the desired N-sulfonylated aziridine derivatives in high to excellent yields with NaBr as the byproduct.     

Silylmetalation of alkenes

Silylmetalation of alkenes is challenging due to the low reactivity of the substrates. In contrast, carbometalation of alkenes has been realized through several innovative methods, including activation of the reagent and the substrate. A similar approach could be applicable to silylmetalation of alkenes, and we have recently developed a bimetal activation method using zincate complexes for this purpose. Here, we describe how the silylzincation of alkenes was achieved. First, the strategies for carbometalation of alkenes will be summarized. Secondly, the history and development of silylzincation chemistry are briefly described. Then the details of our findings related to two types of silylzincation of alkenes, as well as recent progress in mechanistic studies, are discussed. The key point in the silylzincation of alkenes proved to be the bimetal activation of the substrate. One metal (copper or titanium) strongly coordinates and activates the alkene moiety, and the other metal (zinc) acts as the electron acceptor from the silyl group by way of the alkene moiety. This dual activation concept is expected to be applicable to other combinations of metals, as well as to new types of reactions.     

Regioselective and Enantioselective Copper-Catalyzed Hydroaminocarbonylation of Unactivated Alkenes and Alkynes

Given the prevalence of amide backbones in marketed pharmaceuticals and their ubiquity as critical binding units in natural peptides and proteins, it remains important to develop novel methods to construct amide bonds. We report here a general method for the anti-Markovnikov hydroaminocarbonylation of unactivated alkenes under mild conditions, using copper catalysis in combination with hydroxylamine electrophile reagents and poly(methylhydrosiloxane) (PMHS) as a cheap and environmentally friendly hydride source. The reaction tolerates a variety of functional groups and efficiently converts unactivated terminal alkenes, 1,1-disubstituted alkenes, and cyclic alkenes to the corresponding amides with exclusive anti-Markovnikov selectivity (and high enantioselectivities/diastereoselectivities). Additionally, with minimal modification of the reaction conditions, alkynes can also undergo tandem hydrogenation-hydroaminocarbonylation to alkyl amides.     

Recent Advances in the Intermolecular Oxidative Difunctionalization of Alkenes

Functionalization of alkenes has been well investigated by chemists, thus it has been extensively applied in organic synthesis and industries. In the past few decades, transition‐metal, such as palladium, rhodium, gold, iridium, copper and iron, catalyzed functionalization reactions of alkenes have been significantly developed and played vital roles in synthesis. The difunctionalization of alkenes are appealing as an important alternative to the traditional approaches for the construction of useful carbon centers, particularly carbon quaternary centers, which commonly existed as structural motifs in numerous natural products, pharmaceuticals, and biologically active molecules. This account will summarize our recent advances in the intermolecular difunctionalization of alkenes, and also highlight the scope and limitations as well as the mechanisms of these difunctionalization reactions. In general, in this account the difunctionalization of alkenes starting from dicarbofunctionalization will be discussed. Then carboheterofunctionalization of alkenes will be intensively reviewed, and diheterofunctionalization will also be highlighted.     

3-Benzoylisoxazolines by 1,3-Dipolar Cycloaddition: Chloramine-T-Catalyzed Condensation of α-Nitroketones with Dipolarophiles

In this study, 3-benzoylisoxazolines were synthesized by reacting alkenes with various α-nitroketones using chloramine-T as the base. The scope of α-nitroketones and alkenes is extensive, including different alkenes and alkynes to form various isoxazolines and isoxazoles. The use of chloramine-T, as the low-cost, easily handled, moderate base for 1,3-dipolar cycloaddition is attractive.     

Iron(III) porphyrin catalyzed aziridination of alkenes with bromamine-T as nitrene source

[reaction: see text] Iron(III) porphyrin complexes Fe(Por)Cl are effective catalysts for aziridination of alkenes using bromamine-T as the nitrene source. The catalytic system can operate under mild conditions with alkenes as limiting reagents. The aziridination reaction is general and suitable for a wide variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic olefins, as well as alpha,beta-unsaturated esters. For 1,2-disubstituted olefins, the reactions proceeded with moderate to low stereospecificity.     

Tf2NH-catalyzed,highly regio-and stereo-selective synthesis of trisubstituted alkenes and indane derivatives from benzylic alcohols and alkenes

A reaction of benzylic alcohols with alkenes has been developed in the presence of bis(trifluoromethane)sulfonimide for the synthesis of trisubstituted alkenes and indane derivatives with high stereoselectivity.In general,benzylic alcohols react with 1,1-diaryl alkenes to afford trisubstituted alkenes,and the reaction with 1,2-disubstituted and trisubstituted alkenes affords indane derivatives through a [3 + 2] annulation reaction.     

Nickel-Catalyzed Coupling Reactions of Alkenes

Several reactions of simple, unactivated alkenes with electrophiles under nickel(0) catalysis are discussed. The coupling of olefins with aldehydes and silyl triflates provides allylic or homoallylic alcohol derivatives, depending on the supporting ligands and, to a lesser extent, the substrates employed. Reaction of alkenes with isocyanates yields N-alkyl acrylamides. In these methods, alkenes act as the functional equivalents of alkenyl- and allylmetal reagents.     

Chiral Hetero‐ and Carbocyclic Compounds from the Asymmetric Hydrogenation of Cyclic Alkenes

Several types of chiral hetero‐ and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P‐Ligated iridium catalysts reduced six‐membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five‐membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five‐ rather than the six‐membered cyclic alkenes. The major enantiomer formed in the reduction of six‐membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3‐cis‐cyclohexane carboxylates.     

Cyclopropanation of Terminal Alkenes through Sequential Atom‐Transfer Radical Addition/1,3‐Elimination

An operationally simple method to affect an atom‐transfer radical addition of commercially available ICH₂Bpin to terminal alkenes has been developed. The intermediate iodide can be transformed in a one‐pot process into the corresponding cyclopropane upon treatment with a fluoride source. This method is highly selective for the cyclopropanation of unactivated terminal alkenes over non‐terminal alkenes and electron‐deficient alkenes. Due to the mildness of the procedure, a wide range of functional groups such as esters, amides, alcohols, ketones, and vinylic cyclopropanes are well tolerated.     

Gas chromatographic-mass spectrometric characterization of all acyclic C5-C7 alkenes from fluid catalytic cracked gasoline using polydimethylsiloxane and squalane stationary phases

Published retention indices of acyclic alkenes C5-C7 on squalane and polydimethylsiloxane as stationary phases were investigated, and reliable retention indices of alkenes from various sources were converted to separation systems used in a laboratory. Retention indices measured on available authentic commercial alkenes and on alkenic fraction of gasoline, published retention indices as well as means of GC-MS were used for verification of calculated retention indices. Retention of some gas chromatographic unseparated isomer pairs was obtained by mass spectrometric deconvolution using a specific single-ion monitoring. On the basis of these retention data, C5-C7 alkenes were identified and analyzed in the gasoline from fluid catalytic cracking. In the gasoline all 59 acyclic C5-C7 isomeric alkenes were determined at significantly different concentration levels.     

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.     

N-acylsulfonamide assisted tandem C-H olefination/annulation: synthesis of isoindolinones

A tandem C-H olefination/annulation sequence directed by N-acylsulfonamides affords a variety of isoindolinones. This transformation is compatible with aliphatic alkenes as well as conjugated alkenes. Notably, molecular oxygen can be used as the sole, eco-friendly oxidant.     

Intermolecular Radical Carbofluorination of Non‐activated Alkenes

The Meerwein arylation has recently become an even more powerful tool for the functionalization of alkenes. Besides the attachment of an aryl group, radical reactions of this type allow the introduction of several different heteroatoms and a broad variety of alkenes are meanwhile tolerated as substrates. Closing a long‐standing gap of the methodology, this communication describes the first intermolecular Meerwein‐type carbofluorination. In metal‐free reactions, arylalkyl fluorides were obtained from arylhydrazines and alkenes with Selectfluor acting as oxidant and as radical fluorine source.