Iron-Catalyzed, Directed Oxidative Arylation of Olefins with Organozinc and Grignard Reagents

Carboxylate-Assisted Palladium-Catalyzed Regio- and Stereoselective Mizoroki-Heck Arylation of β-Cyclohexadienyl Acrylates and Styrenes

A carboxylate-assisted palladium-catalyzed Mizoroki-Heck arylation of electron-deficient internal alkenes is described herein. This protocol utilized a free carboxylic acid as the directing group for regio- and stereoselective Mizoroki-Heck arylation of β-cyclohexadienyl acrylates and styrenes with various aryl iodides. The synthetic application has been exhibited by decarboxylative aromatization and iodolactonization/hydrolysis of the resulting polyenes providing trisubstituted alkenes and structurally diverse hydroxyl lactones. Additionally, mechanistic studies have been performed to elucidate the reaction outcome of regio- and stereoselectivity.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Nickel-catalyzed intermolecular oxidative Heck arylation driven by transfer hydrogenation

The conventional oxidative Heck reaction between aryl boronic acids and alkenes typically involved the PdII/Pd0/PdII catalytic cycle incorporating an external oxidant and often suffered C=C bond isomerization for internal alkyl-substituted alkenes via chain-walking. Herein, we demonstrate that the regioselectivity (γ-selectivity vs. δ-selectivity) and pathway selectivity (hydroarylation vs. oxidative Heck coupling) of a directed Ni-catalyzed alkene arylation can be controlled by judicious tuning of the coordination environment around the nickel catalyst via optimization of an appropriate phosphine ligand and directing group. In this way, the Ni(0)-catalyzed oxidative Heck arylation that relies on transfer hydrogenation of an acceptor olefin is developed with excellent E/Z selectivity and regioselectivity. Mechanistic investigations suggest that the addition of the acceptor is crucial for lowering the energy for carbometalation and for enabling catalytic turnover.

Development of Metal Nanoparticle Catalysis toward Drug Discovery

Transition-metal nanoparticles (NPs) catalysts supported on solid material represent one of the most important subjects in organic synthesis due to their reliable carbon-carbon or carbon-heteroatom bond-forming cross-coupling reactions. Therefore methodologically and conceptually novel immobilization methods for nonprecious transition-metal NPs are currently required for the development of organic, inorganic, green, materials, and medicinal chemistry. We discovered a self-assembled Au-supported Pd NPs catalyst (SAPd(0)) and applied it as a catalyst to Suzuki-Miyaura coupling, Buchwald-Hartwig reaction, Carbon(sp² and sp³)-Hydrogen bond functionalization, double carbonylation, removal of the allyl protecting groups of allyl esters, and redox switching. SAPd(0) comprises approximately 10 layers of self-assembled Pd(0) NPs, whose size is less than 5 nm on the surface of a sulfur-modified Au. The Pd NPs are wrapped in a sulfated p-xylene polymer matrix. We thought that the self-assembled Au-supported Pd NPs could be made by in situ metal NP and nanospace simultaneous organization (PSSO). This methodology involves 4 kinds of simultaneous procedures: i) reduction of a higher valence metal salt, ii) growth of metal NPs with appropriate size, iii) growth of a matrix with appropriate pores, and iv) wrapping of the metal NPs by matrix nanopores. This methodology is different from previously reported metal NPs-immobilizing methods, which use solid supports with preformed pores or coordination sites. We also applied the in situ PSSO method to prepare various immobilized transition-metal NPs, including base metals. For example, the in situ PSSO method can be applicable to easily prepare Ni, Ru, and Fe NPs with good recyclability and low metal leaching for use in organic synthesis.

Pd-Catalyzed Oxidative Heck Reaction of Grignard Reagents with Diaziridinone as Oxidant

A novel Pd-catalyzed oxidative Heck reaction with readily available Grignard reagents using di- t-butyldiaziridinone as an oxidant has been developed. Various substituted olefins were obtained in 46-91% yields with high regioselectivity under mild reaction conditions.

Ni-catalysed regioselective 1,2-diarylation of unactivated olefins by stabilizing Heck intermediates as pyridylsilyl-coordinated transient metallacycles

We report a Ni-catalysed diarylation of unactivated olefins in dimethylpyridylvinylsilane by intercepting Heck C(sp3)-NiX intermediates, derived from aryl halides, with arylzinc reagents. This approach utilizes a modifiable pyridylsilyl moiety as a coordinating group that plays a dual role of intercepting oxidative addition species to promote Heck carbometallation, and stabilizing the Heck C(sp3)-NiX intermediates as transient metallacycles to suppress β-hydride elimination, and facilitate transmetalation/reductive elimination. This method affords 1,2-diarylethylsilanes, which can be readily oxidized to 1,2-diarylethanols that occur as structural motifs in 3-aryl-3,4-dihydroisocoumarin and dihydrostilbenoid natural products.

Palladium-Catalyzed Formylation of Arylzinc Reagents with S-Phenyl Thioformate

The first example of palladium-catalyzed direct formylation of arylzinc reagents using S-phenyl thioformate is reported. The reaction proceeded under mild conditions, allowing high functional group tolerance. In addition, the developed formylation method was used to prepare deuterated and ¹³C-labeled aryl aldehydes from isotope-labeled S-phenyl thioformates. Moreover, this procedure was applied to an alkenylzinc halide, affording the corresponding enal.

Iron-Catalyzed C-H Bond Activation

Catalytic C-H bond activation, which was an elusive subject of chemical research until the 1990s, has now become a standard synthetic method for the formation of new C-C and C-heteroatom bonds. The synthetic potential of C-H activation was first described for ruthenium catalysis and is now widely exploited by the use of various precious metals. Driven by the increasing interest in chemical utilization of ubiquitous metals that are abundant and nontoxic, iron catalysis has become a rapidly growing area of research, and iron-catalyzed C-H activation has been most actively explored in recent years. In this review, we summarize the development of stoichiometric C-H activation, which has a long history, and catalytic C-H functionalization, which emerged about 10 years ago. We focus in this review on reactions that take place via reactive organoiron intermediates, and we excluded those that use iron as a Lewis acid or radical initiator. The contents of this review are categorized by the type of C-H bond cleaved and the type of bond formed thereafter, and it covers the reactions of simple substrates and substrates possessing a directing group that anchors the catalyst to the substrate, providing an overview of iron-mediated and iron-catalyzed C-H activation reported in the literature by October 2016.

Iron-catalyzed ortho-allylation of aromatic carboxamides with allyl ethers

Arenes possessing an N-(quinolin-8-yl)amide directing group are ortho-allylated with allyl phenyl ether in the presence of an iron/diphosphine catalyst and an organometallic base at 50-70 °C. The reaction proceeds via fast iron-catalyzed C-H activation, followed by reaction of the resulting iron intermediate with the allyl ether in γ-selective fashion.

Iron-catalyzed allylic arylation of olefins via C(sp3)-H activation under mild conditions

An aryl Grignard reagent in the presence of mesityl iodide converts an allylic C-H bond of a cycloalkene or an allylbenzene derivative into a C-C bond in the presence of a catalytic amount of Fe(acac)(3) and a diphosphine ligand at 0 °C. The stereo- and regioselectivity of the reaction, together with deuterium labeling experiments, suggest that C-H bond activation is the slow step in the catalytic cycle preceding the formation of an allyliron intermediate.

Iron-catalyzed chemo- and stereoselective hydromagnesiation of diarylalkynes and diynes

Diarylalkynes are chemo- and stereoselectively hydromagnesiated in high yields at room temperature with an iron species generated in situ from FeCl(2)and EtMgBr. Functional groups such as bromide, iodide, amine, phenoxide, and alkene are well tolerated. Under similar conditions, diynes are chemo-, regio-, and stereoselectively hydromagnesiated. The resulting alkenylmagnesium compounds are a platform for further functionalization as a one-pot reaction.

Iron-catalyzed regio- and stereoselective chlorosulfonylation of terminal alkynes with aromatic sulfonyl chlorides

Terminal alkynes react with aromatic sulfonyl chlorides in the presence of an iron(II) catalyst and a phosphine ligand to give (E)-β-chlorovinylsulfones with 100% regio- and stereoselectivity. Various functional groups, such as chloride, bromide, iodide, nitro, ketone, and aldehyde, are tolerated under the reaction conditions. Addition of tosyl chloride to a 1,6-enyne followed by radical 5-exo-trig cyclization gave an exocyclic alkenylsulfone.

Iron-catalyzed C-H bond activation for the ortho-arylation of aryl pyridines and imines with Grignard reagents

Direct arylation of the ortho-C-H bond of an aryl pyridine or an aryl imine with an aryl Grignard reagent has been achieved by using an iron-diamine catalyst and a dichloroalkane as an oxidant in a short reaction time (e.g., 5 min) under mild conditions (0 °C). The use of an aromatic co-solvent, such as chlorobenzene and benzene, and slow addition of the Grignard reagent are essential for the high efficiency of the reaction. The present arylation reaction has distinct merits over the previously developed reaction that used an arylzinc reagent, such as its reaction rate and atom economy. Selective C-H bond activation occurs in the presence of a leaving group, such as a tosyloxy, chloro, and bromo group. Studies on a stoichiometric reaction and kinetic isotope effects shed light on the reaction intermediate and the C-H bond-activation step.