Dinickel-Catalyzed N=N Coupling Reactions for the Synthesis of Hindered Azoarenes.

Azoarenes are the largest class of photoswitching molecules, and they have a broad range of applications in photopharmacology and materials science. Azoarenes possessing -substitution often display improved properties, including isomerization under visible light irradiation, near-quantitative switching, and long thermal half-lives in the form. The synthesis of hindered -substituted azoarenes is often low-yielding using established oxidative or reductive coupling methods.

Rapid depletion of "catch-and-release" anti-ASGR1 antibody in vivo.

Targeting antigens with antibodies exhibiting pH/Ca-dependent binding against an antigen is an attractive strategy to mitigate target-mediated disposition and antigen buffering. Studies have reported improved serum exposure of antibodies exhibiting pH/Ca-binding against membrane-bound receptors. Asialoglycoprotein receptor 1 (ASGR1) is a membrane-bound receptor primarily localized in hepatocytes.

Redox Approaches to Carbene Generation in Catalytic Cyclopropanation Reactions.

Transition metal-catalyzed carbene transfer reactions have a century-old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents.

Catalytic Asymmetric Synthesis of Zinc Metallacycles.

Transition-metal-catalyzed reductive coupling reactions of alkynes and imines are attractive methods for the synthesis of chiral allylic amines. Mechanistically, these reactions involve oxidative cyclization of the alkyne and the imine to generate a metallacyclic intermediate, which then reacts with H or a H surrogate to form the product. As an alternative to this hydrogenolysis pathway, here we show that transmetalation to zinc can occur, forming a zinc metallacycle product.

Nucleophilic Carbenes Derived from Dichloromethane.

Nickel PyBox catalysts promote nucleophilic cyclopropanation reactions using CH Cl as a methylene source and Mn as a stoichiometric reductant. The substrate scope includes a broad range of alkenes bearing electron-withdrawing substituents, including esters, amides, ketones, nitriles, sulfones, phosphonate esters, trifluoromethyl groups, and electron-deficient arenes. Enantioselective cyclopropanations of α,β-unsaturated esters have been developed using chiral PyBox ligands.

Catalytic Asymmetric Ring-Opening Reactions of Unstrained Heterocycles Using Cobalt Vinylidenes.

Cobalt catalysts promote highly enantioselective ring-opening reactions of 2,5-dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2+2]-cycloaddition pathway.

Catalytic Asymmetric Cyclopropanations with Nonstabilized Carbenes.

Cyclopropanes are common building blocks in pharmaceuticals, agrochemicals, and organic materials. The most general methods for the synthesis of chiral cyclopropanes are catalytic additions of diazoalkanes to alkenes. However, a limitation of this approach is that diazoalkanes can only be safely handled on preparative scales if they possess stabilizing substituents.

Dinickel-Catalyzed N═N Bond Rotation.

Azoarenes function as molecular switches that can be triggered by external stimuli, such as heat, light, and electrochemical potential. Here, we show that a dinickel catalyst can induce cis/trans isomerization in azoarenes through a N═N bond rotation mechanism. Catalytic intermediates containing azoarenes bound in both the cis and trans forms are characterized.

A dinickel-catalyzed three-component cycloaddition of vinylidenes.

A dinickel catalyst promotes the [2 + 2 + 1]-cycloaddition of two aldehyde equivalents and a vinylidene. The resulting methylenedioxolane products can be deprotected in one pot under acidic conditions to reveal α-hydroxy ketones. This method provides convenient access to unsymmetrical alkyl-substituted α-hydroxy ketones, which are challenging to synthesize selectively using cross-benzoin reactions.

Dinickel Catalyzed Vinylidene-Alkene Cyclization Reactions.

A dinickel catalyst promotes reductive cyclization reactions of 1,1-dichloroalkenes containing pendant olefins. The reactions can be conducted with a Zn reductant or electrocatalytically using a carbon working electrode. Mechanistic studies are consistent with the intermediacy of a Ni(vinylidene) species, which adds to the alkene and generates a metallacyclic intermediate.

Catalytic Reductive Carbene Transfer Reactions.

Efforts to develop catalytic carbene transfer reactions have largely relied on the use of diazo precursors. However, diazoalkanes are susceptible to undergoing violent exothermic decomposition unless they contain stabilizing substituents. Consequently, most synthetic methods are restricted to diazoacetates or related derivatives.

Dinickel Active Sites Supported by Redox-Active Ligands.

Redox reactions that take place in enzymes and on the surfaces of heterogeneous catalysts often require active sites that contain multiple metals. By contrast, there are very few homogeneous catalysts with multinuclear active sites, and the field of organometallic chemistry continues to be dominated by the study of single metal systems. Multinuclear catalysts have the potential to display unique properties owing to their ability to cooperatively engage substrates.

Nickel Catalyzed Vinylidene Insertions into O-H Bonds.

A (pybox)Ni catalyst (pybox = pyridine-bis(oxazoline)) promotes the reductive cyclization of β-hydroxy 1,1-dichloroalkenes to form 2,3-dihydrofurans. The substrates for this reaction are conveniently prepared by an aldol addition followed by one-carbon homologation. Chiral substrates are accessible in highly enantioenriched form, allowing for the synthesis of stereochemically complex 2,3,4-trisubstituted products.

Catalytic Synthesis of Conjugated Azopolymers from Aromatic Diazides.

Conjugated polymers containing main chain azoarene repeat units are synthesized by a dinickel catalyzed N=N coupling reaction of aromatic diazides. The polymerization exhibits broad substrate scope and is compatible with heterocycles commonly featured in high performance organic materials, including carbazole, thiophene, propylenedioxythiophene (ProDOT), diketopyrrolopyrrole (DPP), and isoindigo. Copolymerizations can be carried out using monomer mixtures, and monoazide chain stoppers can be used to install well-defined end groups.

Cobalt Catalyzed Reductive Spirocyclopropanation Reactions.

Cobalt pyridine-diimine (PDI) complexes catalyze the reductive spirocyclopropanation of terminal 1,3-dienes. -Dichlorocycloalkanes serve as carbene precursors and Zn is used as a terminal electron source. The reaction is effective for a range of -dichloro partners including those containing sulfur and nitrogen heterocycles.

Nickel-catalyzed insertions of vinylidenes into Si-H bonds.

A nickel-catalyzed reductive cyclization of 1,1-dichloroalkenyl silanes is reported. The products of this reaction are unsaturated five- or six-membered silacycles. Intermolecular variants are also described, providing access to trisubstituted vinyl silanes that are not accessible by alkyne hydrosilylation or sila-Heck-type processes.

A Dinickel Catalyzed Cyclopropanation without the Formation of a Metal Carbene Intermediate.

(NDI)Ni catalysts (NDI=naphthyridine-diimine) promote cyclopropanation reactions of 1,3-dienes using (Me Si)CHN . Mechanistic studies reveal that a metal carbene intermediate is not part of the catalytic cycle. The (NDI)Ni (CHSiMe ) complex was independently synthesized and found to be unreactive toward dienes.

-Symmetric Dinickel Catalysts for Enantioselective [4 + 1]-Cycloadditions.

Dinickel naphthyridine-bis(oxazoline) catalysts promote enantioselective intermolecular [4 + 1]-cycloadditions of vinylidene equivalents and 1,3-dienes. The products of this reaction are methylenecyclopentenes, and the exocyclic alkene is generally obtained with high selectivity. - and -dienes react in a stereoconvergent fashion, providing cycloadducts with the same sense of absolute stereochemistry and nearly identical ee values.

Catalytic [5 + 1]-Cycloadditions of Vinylcyclopropanes and Vinylidenes.

Polysubstituted cyclohexenes bearing 1,3 () substitution patterns are challenging to access using the Diels-Alder reaction (the - rule). Here, we report a cobalt-catalyzed reductive [5 + 1]-cycloaddition between a vinylcyclopropane and a vinylidene to provide methylenecyclohexenes bearing all- relationships. Vinylidene equivalents are generated from 1,1-dichloroalkenes using Zn as a stoichiometric reductant.

Carbene Formation and Transfer at a Dinickel Active Site.

The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [ NDI]Ni(CH) complex (NDI = naphthyridine-diimine) reacts with PhCN to generate a metastable diazoalkane adduct, which eliminates N at 60 °C to yield a paramagnetic Ni(μ-CPh) complex. The Ni(μ-CPh) complex undergoes carbene transfer to -BuNC via an initial isonitrile adduct, which, upon heating, releases free -BuNCCPh.

Separation of gold and other rare materials from an ensemble of heterogeneous particles using a NdFeB magnetic circuit.

Most solid particles, composed of diamagnetic or weak paramagnetic materials, cannot be extracted by a conventional magnetic separator. Here we report that an ensemble of heterogeneous particles, composed of bismuth, gold, graphite and rock forming minerals are separated into fractions of different materials by small NdFeB magnetic plates. It is based on a recent finding that acceleration of a translating particle, induced by magnetic volume force in an area of field gradient, is uniquely determined by intrinsic susceptibility of material; the acceleration is independent to particle mass.

Catalytic reductive [4 + 1]-cycloadditions of vinylidenes and dienes.

Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + 1]-cycloaddition reactions of 1,3-dienes.

Catalytic Cyclooligomerization of Enones with Three Methylene Equivalents.

Cyclic structures are highly represented in organic molecules, motivating a wealth of catalytic methods targeting their synthesis. Among the various ring-forming processes, cyclooligomerization reactions possess several attractive features but require addressing a unique challenge associated with controlling ring-size selectivity. Here we describe the catalytic reductive cocyclooligomerization of an enone and three carbene equivalents to generate a cyclopentane, a process that constitutes a formal [2 + 1 + 1 + 1]-cycloaddition.

Cobalt-Catalyzed Reductive Dimethylcyclopropanation of 1,3-Dienes.

Dimethylcyclopropanes are valuable synthetic targets that are challenging to access in high yield using Zn carbenoid reagents. Herein, we describe a cobalt-catalyzed variant of the Simmons-Smith reaction that enables the efficient dimethylcyclopropanation of 1,3-dienes using a Me CCl /Zn reagent mixture. The reactions proceed with high regioselectivity based on the substitution pattern of the 1,3-diene.

Regioselective Simmons-Smith-type cyclopropanations of polyalkenes enabled by transition metal catalysis.

A [ PDI]CoBr complex (PDI = pyridine-diimine) catalyzes Simmons-Smith-type reductive cyclopropanation reactions using CHBr in combination with Zn. In contrast to its non-catalytic variant, the cobalt-catalyzed cyclopropanation is capable of discriminating between alkenes of similar electronic properties based on their substitution patterns: monosubstituted > 1,1-disubstituted > ()-1,2-disubstituted > ()-1,2-disubstituted > trisubstituted. This property enables synthetically useful yields to be achieved for the monocyclopropanation of polyalkene substrates, including terpene derivatives and conjugated 1,3-dienes.