Cobalt(II)-Catalyzed Stereoselective Olefin Isomerization: Facile Access to Acyclic Trisubstituted Alkenes

Iron-Catalyzed Tunable Alkene Migratory Silylation and Transposition

The example of iron-catalyzed alkenes migratory silylation and transposition has been demonstrated, affording a tunable approach to synthesize thermodynamically stable allylsilanes and internal alkenes with high efficiency and regioselectivity. These reactions showcase several advantageous features, including good functional group tolerance, excellent regioselectivity, a broad substrate scope, scalability to gram-scale synthesis, and late-stage functionalization of bio-relevant molecules. Furthermore, the relay catalytic mechanism of the migratory silylation, involving both iron-silyl and iron-hydride intermediates, provides valuable insights into iron-catalyzed coupling reactions, opening new avenues for the development of novel transformations under iron catalysis.

Proton-Modulated Nickel Hydride Electrocatalysis for the Hydrogenation of Unsaturated Bonds and Olefin Isomerization

Transition-metal hydrides stand as indispensable intermediates in both energy conversion and organic synthesis. Their electrochemical generation represents a compelling sustainable approach, enabling precise control over the reactivity and expanding the scope of electrocatalytic hydrogenation and isomerization. However, a major challenge in Ni-catalyzed electrochemical hydrogenation is the competing hydrogen evolution reaction (HER), which has led to various innovative strategies aimed at circumventing Ni-H formation. Here, we pursued an alternative approach by designing a bifunctional ligand with a pendant amine moiety to promote Ni-H formation. This design enabled selective (semi)hydrogenation of a diverse range of substrates, including terminal and internal alkynes, alkenes, and aldehydes, achieving an unprecedented substrate scope. Remarkably, we also demonstrated tunable positional selectivity for olefin isomerization by employing different types of proton sources. Our hydrogenation and isomerization method also exhibits excellent functional group tolerance, streamlining access to pharmaceuticals and their derivatives. Computational studies revealed the crucial, noninnocent role of the proton source in modulating metal hydride selectivity, either through hydrogen bonding, direct protonation of the pendant amine, or facilitation of protodemetalation.

Co(II)-catalyzed isomerization of enals using hydrogen atom transfer

To develop a process for the synthesis of an enal acetate, the so called C5-acetate that is important in the industrial preparation of vitamin A, we show here that Co(II)-based hydrogen atom transfer catalysts under H2 promote such isomerizations in high yield with low catalyst loading (0.1 mol%). D-labelling studies suggest the enal isomerization process and catalyst activation by H2 to be reversible.

Tungsten-catalyzed stereodivergent isomerization of terminal olefins

Catalytic alkene isomerization is a powerful synthetic strategy for preparing valuable internal alkenes from simple feedstocks. The utility of olefin isomerization hinges on the ability to control both positional and stereoisomerism to access a single product among numerous potential isomers. Within base-metal catalysis, relatively little is known about how to modulate reactivity and selectivity with group 6 metal-catalyzed isomerization. Here, we describe a tungsten-catalyzed, positionally selective alkene isomerization reaction in which tuning the ligand environment grants access to either the E- or Z-stereoisomer. The reactions employ simple, commercially available precatalysts and ligands. Preliminary mechanistic studies suggest that the ligand environment around 7-coordinate tungsten is crucial for stereoselectivity, and that substrate directivity prevents over-isomerization to the conjugated alkene. These features allow for exclusive formation of β,γ-unsaturated carbonyl compounds that are otherwise difficult to prepare.

N2 Dissociation vs Reversible 1,2-Methyl Migration in PCNHCP Cobalt(I) Complexes in the Stereoselective Isomerization (E/Z) of Allyl Ethers

With growing efforts pushing toward sustainable catalysis, using earth-abundant metals has become increasingly important. Here, we present the first examples of cobalt PCNHCP pincer complexes that demonstrate dual stereoselectivity for allyl ether isomerization. While the cationic cobalt complex [((PCNHCP)Co)2-μ-N2][BAr4 F]2 (3) mainly favors the Z-isomer of the enol ether, the corresponding methyl complex [(PCNHCP)CoMe] (4) mostly gives the E-isomer. The dichotomy in selectivity was investigated computationally, revealing important contributions from the substituents on the metal (N2 vs Me), including a 1,2-alkyl migration from cobalt to the N-heterocyclic carbene (NHC) of the methyl substituent, which is further explored in this report.

Cobalt-Hydride-Catalyzed Alkene-Carboxylate Transposition (ACT) of Allyl Carboxylates

The alkene-carboxylate transposition (ACT) of allyl carboxylates is one of the most atom-economic and synthetically reliable transformations in organic chemistry, as allyl carboxylates are versatile synthetic intermediates. Classic ACT transformations, including [3,3]-sigmatropic rearrangement and transition metal-catalyzed allylic rearrangement, typically yield 1,2-alkene/1,3-acyloxy shifted products through a two-electron process. However, position-altered ACT to produce distinct 1,3-alkene/1,2-acyloxy shifted products remains elusive. Here, we report the first cobalt-hydride-catalyzed ACT of allyl carboxylates, enabling access to these unprecedented 1,3-alkene/1,2-acyloxy shifted products via a 1,2-radical migration (RaM) strategy. This transformation demonstrates broad functional group tolerance, is suitable for late-stage modification of complex molecules, and is amenable to gram-scale synthesis. It also expands the reaction profiles of both allyl carboxylates and cobalt catalysis. Preliminary experimental and computational studies suggest a mechanism involving metal-hydride hydrogen atom transfer (MHAT) and the 1,2-RaM process. This reaction is expected to serve as the basis for the development of versatile Co-H-catalyzed transformations of allyl carboxylates, generating a wide array of valuable building blocks for synthetic, medicinal, and materials chemistry.

Methoxide-Enabled Zirconium-Catalyzed Migratory Alkene Hydrosilylation

A zirconocene dichloride-catalyzed alkene hydrosilylation is reported that can be applied to non-activated and conjugated terminal and internal alkenes. It involves a catalytic Zr-walk process and leads to a selective conversion to the linear product. Lithium methoxide serves as mild catalyst activating agent, which significantly increases the applicability and operational simplicity in comparison to earlier zirconium(II)-based protocols. Supported by additional experiments and calculations, a mechanism via zirconium(IV) intermediates is proposed. Due to the benign nature and ready-availability of the zirconium catalyst, the reaction is an attractive alternative to established alkene hydrosilylation methods.

(Z)-Selective Isomerization of 1,1-Disubstituted Alkenes by Scandium-Catalyzed Allylic C-H Activation

The isomerization of 1,1-disubstituted alkenes through 1,3-hydrogen shift is an atom-efficient route for synthesizing trisubstituted alkenes, which are important moieties in many natural products, pharmaceuticals, and organic materials. However, this reaction often encounters regio- and stereoselectivity challenges, typically yielding E/Z-mixtures of the alkene products or thermodynamically favored (E)-alkenes. Herein, we report the (Z)-selective isomerization of 1,1-disubstituted alkenes to trisubstituted (Z)-alkenes via the regio- and stereospecific activation of an allylic C-H bond. The key to the success of this unprecedented transformation is the use of a sterically demanding half-sandwich scandium catalyst in combination with a bulky quinoline compound, 2-tert-butylquinoline. Deuterium-labeling experiments and density functional theory (DFT) calculations have revealed that 2-tert-butylquinoline not only facilitates the C═C bond transposition through hydrogen shuttling but also governs the regio- and stereoselectivity due to the steric hindrance of the tert-butyl group. This protocol enables the synthesis of diverse (Z)-configured acyclic trisubstituted alkenes and endocyclic trisubstituted alkenes from readily accessible 1,1-disubstituted alkenes. It offers an efficient and selective route for preparing a new family of synthetically challenging (Z)-trisubstituted alkenes with broad substrate scope, 100% atom efficiency, high regio- and stereoselectivity, and an unprecedented reaction mechanism.

Alkene Isomerization Catalyzed by a Mn(I) Bisphosphine Borohydride Complex

An additive-free manganese-catalyzed isomerization of terminal alkenes to internal alkenes is described. This reaction is implementing an inexpensive nonprecious metal catalyst. The most efficient catalyst is the borohydride complex cis-[Mn(dippe)(CO)2(κ2-BH4)]. This catalyst operates at room temperature, with a catalyst loading of 2.5 mol %. A variety of terminal alkenes is effectively and selectively transformed into the respective internal E-alkenes. Preliminary results show chain-walking isomerization at an elevated temperature. Mechanistic studies were carried out, including stoichiometric reactions and in situ NMR analysis. These experiments are flanked by computational studies. Based on these, the catalytic process is initiated by the liberation of "BH3" as a THF adduct. The catalytic process is initiated by double bond insertion into an M-H species, leading to an alkyl metal intermediate, followed by β-hydride elimination at the opposite position to afford the isomerization product.

Alkene Isomerization Using a Heterogeneous Nickel-Hydride Catalyst

Transition metal-catalyzed alkene isomerization is an enabling technology used to install an alkene distal to its original site. Due to their well-defined structure, homogeneous catalysts can be fine-tuned to optimize reactivity, stereoselectivity, and positional selectivity, but they often suffer from instability and nonrecyclability. Heterogeneous catalysts are generally highly robust but continue to lack active-site specificity and are challenging to rationally improve through structural modification. Known single-site heterogeneous catalysts for alkene isomerization utilize precious metals and bespoke, expensive, and synthetically intense supports. Additionally, they generally have mediocre reactivity, inspiring us to develop a heterogeneous catalyst with an active site made from readily available compounds made of Earth-abundant elements. Previous work demonstrated that a very active homogeneous catalyst is formed upon protonation of Ni[P(OEt)3]4 by H2SO4, generating a [Ni-H]+ active site. This catalyst is incredibly active, but also decomposes readily, which severely limits its utility. Herein we show that by using a solid acid (sulfated zirconia, SZO300), not only is this decomposition prevented, but high activity is maintained, improved selectivity is achieved, and a broader scope of functional groups is tolerated. Preliminary mechanistic experiments suggest that the catalytic reaction likely goes through an intermolecular, two-electron pathway. A detailed kinetic study comparing the state-of-the-art Ni and Pd isomerization catalysts reveals that the highest activity and selectivity is seen with the Ni/SZO300 system. The reactivity of Ni/SZO300, is not limited to alkene isomerization; it is also a competent catalyst for hydroalkenylation, hydroboration, and hydrosilylation, demonstrating the broad application of this heterogeneous catalyst.

Stereodivergent, Kinetically Controlled Isomerization of Terminal Alkenes via Nickel Catalysis

Because internal alkenes are more challenging synthetic targets than terminal alkenes, metal-catalyzed olefin mono-transposition (i.e., positional isomerization) approaches have emerged to afford valuable E- or Z- internal alkenes from their complementary terminal alkene feedstocks. However, the applicability of these methods has been hampered by lack of generality, commercial availability of precatalysts, and scalability. Here, we report a nickel-catalyzed platform for the stereodivergent E/Z-selective synthesis of internal alkenes at room temperature. Commercial reagents enable this one-carbon transposition of terminal alkenes to valuable E- or Z-internal alkenes via a Ni-H-mediated insertion/elimination mechanism. Though the mechanistic regime is the same in both systems, the underlying pathways that lead to each of the active catalysts are distinct, with the Z-selective catalyst forming from comproportionation of an oxidative addition complex followed by oxidative addition with substrate and the E-selective catalyst forming from protonation of the metal by the trialkylphosphonium salt additive. In each case, ligand sterics and denticity control stereochemistry and prevent over-isomerization.

Palladium-Catalyzed Hydrocyanation of Ynoates: En Route to the Stereodivergent Synthesis of β-Cyanated α,β-Unsaturated Esters via Ligand Controlled Regio- and Stereoselectivity

A Pd-catalyzed highly regio- and stereoselective hydrocyanation was developed, providing a novel approach to the stereodivergent synthesis of β-cyano-substituted acrylates in good yields with a wide substrate scope. The judicious selection of ligands was crucial for elegant control over the stereodivergence. Furthermore, the success of the E-hydrocyanation hinges on the right matching of Pd and L1, which not only ensured the catalytic activity but also prevented the formation of α-cyanation products.

Direct synthesis of branched amines enabled by dual-catalyzed allylic C─H amination of alkenes with amines

Direct conversion of hydrocarbons into amines represents an important and atom-economic goal in chemistry for decades. However, intermolecular cross-coupling of terminal alkenes with amines to form branched amines remains extremely challenging. Here, a visible-light and Co-dual catalyzed direct allylic C─H amination of alkenes with free amines to afford branched amines has been developed. Notably, challenging aliphatic amines with strong coordinating effect can be directly used as C─N coupling partner to couple with allylic C─H bond to form advanced amines with molecular complexity. Moreover, the reaction proceeds with exclusive regio- and chemoselectivity at more steric hinder position to deliver primary, secondary, and tertiary aliphatic amines with diverse substitution patterns that are difficult to access otherwise.

A Neutral PCNHCP Co(I)-Me Pincer Complex as a Catalyst for N-Allylic Isomerization with a Broad Substrate Scope

Earth-abundant-metal catalyzed double bond transposition offers a sustainable and atom-economical route toward the synthesis of internal alkenes. With an emphasis specifically on internal olefins and ethers, the isomerization of allylic amines has been particularly under represented in the literature. Herein, we report an efficient methodology for the selective isomerization of N-allylic organic compounds, including amines, amides, and imines. The reaction is catalyzed by a neutral PCNHCP cobalt(I) pincer complex and proceeds via a π-allyl mechanism. The isomerization occurs readily at 80-90 °C, and it is compatible with a wide variety of functional groups. The in situ formed enamines could additionally be used for a one-pot inverse-electron-demand Diels-Alder reaction to furnish a series of diversely substituted heterobiaryls, which is further discussed in this report.

Quantum Chemical Insight into 1,2-Shift Rearrangement in Bromination of Allylaryls

In this work, we have provided mechanistic insight into the addition of bromine to an allylic double bond of allylaryl derivatives using experimental and DFT-based electronic structure methods. The experimental yields indicate the influence of the functional group on the aryl ring on the ratio of 1,2-dibromo and 1,3-dibromo adducts formed in the reaction. The optimized geometry and the electron density maps of the allylaryls and their cationic intermediates from DFT simulations revealed that electron-rich aryl rings promoted formation of cationic spiro[2.5] intermediate II, whereas electron-poor aryl rings resulted in formation of bromonium intermediate I. It was observed that electron-rich allylaryls promoted the 1,2-shift of the aryl ring that resulted in bond formation between the carbon atom (C1) on the aryl ring and the central carbon atom (C3) in the allylic double bond and formed spiro[2.5] intermediate II, a trend which was confirmed by harmonic oscillator model of aromaticity index. Also, Wiberg bond order analysis is in good agreement with the experimental work. Thermochemical analysis indicates that smaller C1···C3 distance resulted in favorable values for the difference in free energy change (ΔΔG). The favorable ΔΔG values are a result of higher electron density on the aryl ring, making it more nucleophilic toward C3 carbon and promoting 1,2-shift that led to formation of the spiro[2.5] intermediate. Thus, the underlying mechanism indicates that the electron-rich allylaryls promote the formation of 1,3-dibromo compounds through formation and stabilization of the spiro[2.5] intermediate II.

Electrochemically Generated Carbanions Enable Isomerizing Allylation and Allenylation of Aldehydes with Alkenes and Alkynes

The direct coupling of aldehydes with petrochemical feedstock alkenes and alkynes would represent a practical and streamlined approach for allylation and allenylation chemistry. However, conventional approaches commonly require preactivated substrates or strong bases to generate allylic or propargylic carbanions and only afford branched allylation or propargylation products. Developing a mild and selective approach to access synthetically useful linear allylation and allenylation products is highly desirable, albeit with formidable challenges. We report a strategy using hydrogen evolution reaction (HER) to generate a carbanion from weakly acidic sp³ C-H bonds (pK_a ∼ 35-40) under mild reaction conditions, obviating the use of strong bases, Schlenk techniques, and multistep procedures. The cathodically generated carbanion reverses the typical reaction selectivity to afford unconventional isomerizing allylation and allenylation products (125 examples). The generation of carbanions was monitored and identified by in situ ultraviolet-visible (UV-vis) spectroelectrochemistry. Furthermore, we extended this protocol to the generation of other carbanions and their application in coupling reactions between alcohols with carbanions. The appealing features of this approach include mild reaction conditions, excellent functional group tolerance, unconventional chemo- and regioselectivity, and the diverse utility of products, which includes offering direct access to diene luminophores and bioactive scaffolds. We also performed cyclic voltammetry, control experiments, and density functional theory (DFT) calculations to rationalize the observed reaction selectivity and mechanism.

Carboazidation of Terminal Alkenes with Trimethylsilyl Azide and Cyclic Ethers Catalyzed by Copper Powder under Oxidative Conditions

Copper-catalyzed carboazidation of alkenes with trimethylsilyl azide and cyclic ethers has been achieved. The employment of naturally abundant copper catalysts allowed cyclic ethers to be used as alkylating reagents under oxidative conditions. The use of styrene derivatives and 1,1-diaryl alkenes afforded carboazidation products. In addition, application of five- and six-membered cyclic ethers to the present reaction gave target organic molecules bearing azide and cyclic ether groups with perfect regioselectivity. Radical trapping and clock experiments revealed that the present reaction proceeded via the radical pathway. To further demonstrate the utility of this carboazidation reaction, transformations from the azide group to the related nitrogen-containing compounds were also performed.

Iron-Catalyzed Oxidative α-Amination of Ketones with Primary and Secondary Sulfonamides

We report the iron-catalyzed α-amination of ketones with sulfonamides. Using an oxidative coupling approach, ketones can be directly coupled with free sulfonamides, without the need for prefunctionalization of either substrate. Primary and secondary sulfonamides are both competent coupling partners, with yields from 55% to 88% for deoxybenzoin-derived substrates.

B(C6 F5 )3 -Catalyzed E-Selective Isomerization of Alkenes

Herein, we report the B(C₆ F₅ )₃ -catalyzed E-selective isomerization of alkenes. The transition-metal-free method is applicable across a diverse array of readily accessible substrates, giving access to a broad range of synthetically useful products containing versatile stereodefined internal alkenes. The reaction mechanism was investigated by using synthetic and computational methods.

Switching between Hydrogenation and Olefin Transposition Catalysis via Silencing NH Cooperativity in Mn(I) Pincer Complexes

While Mn-catalyzed (de)hydrogenation of carbonyl derivatives has been well established, the reactivity of Mn hydrides with olefins remains very rare. Herein, we report a Mn(I) pincer complex that effectively promotes site-controlled transposition of olefins. This reactivity is shown to emerge once the N–H functionality within the Mn/NH bifunctional complex is suppressed by alkylation. While detrimental for carbonyl (de)hydrogenation, such masking of the cooperative N–H functionality allows for the highly efficient conversion of a wide range of allylarenes to higher-value 1-propenybenzenes in near-quantitative yield with excellent stereoselectivities. The reactivity toward a single positional isomerization was also retained for long-chain alkenes, resulting in the highly regioselective formation of 2-alkenes, which are less thermodynamically stable compared to other possible isomerization products. The detailed mechanistic analysis of the reaction between the activated Mn catalyst and olefins points to catalysis operating via a metal–alkyl mechanism—one of the three conventional transposition mechanisms previously unknown in Mn complexes.

Aggregation-Induced Synthesis (AIS): Asymmetric Synthesis via Chiral Aggregates

A new chiral aggregate-based tool for asymmetric synthesis has been developed by taking advantage of chiral aggregates of GAP (Group-Assisted Purification) reagents, N-phosphonyl imines. This tool was proven to be successful in the asymmetric GAP synthesis of functionalized 2,3-dihydrobenzofurans by reacting salicyl N-phosphonyl imines with dialkyl bromomalonates in various cosolvent systems. The chiral induction can be controlled by differentiating between two asymmetric directions simply by changing the ratios of cosolvents which are commonly adopted in AIE (aggregation-induced emission) systems. The formation of chiral aggregates was witnessed by a new analytical tool—aggregation-induced polarization (AIP). The present synthetic method will be broadly extended for general organic synthesis, particularly, for asymmetric synthesis and asymmetric catalysis in the future.

Cobalt-catalyzed branched selective hydroallylation of terminal alkynes

Here, we reported a cobalt-hydride-catalyzed Markovnikov-type hydroallylation of terminal alkynes with allylic electrophile to access valuable and branched skipped dienes (1,4-dienes) with good regioselectivity. This operationally simple protocol exhibits excellent functional group tolerance and exceptional substrate scope. The reactions could be carried out in gram-scale with TON (turn over number) up to 1160, and the products could be easily derivatized. The preliminary mechanism of electrophilic allylation of α-selective cobalt alkenyl intermediate was proposed based on deuterium labeling experiment and kinetic studies.

Selectively generating “skipped” dienes, where two carbon–carbon double bonds are separated by a saturated carbon center, is an interesting problem in organic chemistry, with few reliable, catalytic methods currently available. Here, the authors report branched selective hydroallylation of terminal alkynes with allylic bromides to form skipped dienes, via cobalt catalysis.

Cobalt-Catalyzed Migration Isomerization of Dienes

A cobalt-catalyzed multipositional isomerization of conjugated dienes has been reported for the first time using an 8-oxazoline iminoquinoline ligand. This reaction is operationally simple and atom-economical using readily available starting materials with an E/Z mixture to access disubstituted 1,3-dienes with excellent yields and good E,E stereoselectivity. The mechanism via alkene insertion of cobalt hydride species and β-H elimination of a π-allyl cobalt intermediate is proposed on the basis of deuterium labeling and control experiments and density functional theory calculations.

Two-Stage Syntheses of Clionastatins A and B

A concise and divergent synthesis of the polychlorinated marine steroids clionastatin A and B from inexpensive testosterone has been achieved through a unique two-stage chlorination-oxidation strategy. Key features of the two-stage synthesis include (1) conformationally controlled, highly stereoselective dichlorination at C1 and C2 and C4-OH-directed C19 oxygenation followed by a challenging neopentyl chlorination to install three chlorine atoms; (2) desaturation through one-pot photochemical dibromination-reductive debromination and anti-Markovnikov olefin oxidation by photoredox-metal dual catalysis to enhance the oxidation level of the backbone; and (3) Wharton transposition to furnish the D-ring enone. This synthesis proved that the introduction of the C19 chloride in the early stage of the synthesis secured the stability of the backbone against susceptibility to aromatization during the oxidation stage.

From Center-to-Multilayer Chirality: Asymmetric Synthesis of Multilayer Targets with Electron-Rich Bridges

Asymmetric synthesis of new atropisomerically multilayered chiral targets has been achieved by taking advantage of the strategy of center-to-multilayer chirality and double Suzuki-Miyaura couplings. Diastereomers were readily separated via flash column chromatography and well characterized. Absolute configuration assignment was determined by X-ray structural analysis. Five enantiomerically pure isomers possessing multilayer chirality were assembled utilizing anchors involving electron-rich aromatic connections. An overall yield of 0.69% of the final target with hydroxyl attachment was achieved over 11 steps from commercially available starting materials.

Cobalt-Catalyzed Z to E Geometrical Isomerization of 1,3-Dienes

An efficient cobalt-catalyzed geometrical isomerization of 1,3-dienes is described. In the combination of a CoCl₂ precatalyst with an amido-diphosphine-oxazoline ligand, the geometrical isomerization of E/Z mixtures of 1,3-dienes proceed in a stereoconvergent manner, affording (E) isomers in high stereoselectivity. This facile transformation features a broad substrate scope with good functional group tolerance and could be scaled up to the gram scale smoothly with a catalyst loading of 1 mol %.

HFIP as Protonation Reagent and Solvent for Regioselective Alkylation of Indoles with All-Carbon Centers

The regio- and chemoselective construction of indole bearing an all-carbon center at the C3-position, a versatile bioactive building block, by C(sp²)-C(sp³) formation with olefins has been achieved through utilization of hexafluoroisopropanol (HFIP) as the protonation reagent and solvent. The catalytic reactions are operationally simple and green compared with previous reports utilizing elaborated olefins and catalysts. This protocol allows for alkylation of a variety of substituted indoles with diverse of styrene type alkenes in excellent yields and with high selectivity. Application of this protocol to the synthesis of drug was pursued and with an improved yield in contrast to previous art. Catalytic kinetics and deuterium-labeling experiments suggest that the rate-determining step involves the protonation of olefin by HFIP to generate carbocation, followed by electrophilic addition to indole derivative.

Pd-Catalyzed Coupling of N-Tosylhydrazones with Benzylic Phosphates: Toward the Synthesis of Di- or Tri-Substituted Alkenes

This study shows that various di- and tri-substituted alkenes with high chemoselectivity were obtained in good to high yields by coupling N-tosylhydrazones (NTHs) with benzylic phosphates as electrophilic partners. The obtained new catalytic system consisted of PdCl₂(CH₃CN)₂/dppp, LiOtBu as a base, and cyclopentyl methyl ether as a green solvent. In addition, we performed a gram-scale transformation using NTH derivatives and benzylic phosphates having a C sp²-Cl bond. The latter was used as a starting point for further postfunctionalization of the key intermediates.

Highly selective acid-catalyzed olefin isomerization of limonene to terpinolene by kinetic suppression of the overreactions in a confined space of porous metal-macrocycle framework

Natural enzymes control the intrinsic reactivity of chemical reactions in the natural environment, giving only the necessary products. In recent years, challenging research on the reactivity control of terpenes with structural diversity using artificial host compounds that mimic such enzymatic reactions has been actively pursued. A typical example is the acid-catalyzed olefin isomerization of (+)-limonene, which generally gives a complex mixture due to over-isomerization to thermodynamically favored isomers. Herein we report a highly controlled conversion of (+)-limonene by kinetic suppression of over-isomerization in a confined space of a porous metal–macrocycle framework (MMF) equipped with a Brønsted acid catalyst. The terminal double bond of (+)-limonene migrated to one neighbor, preferentially producing terpinolene. This reaction selectivity was in stark contrast to the homogeneous acid-catalyzed reaction in bulk solution and to previously reported catalytic reactions. X-ray structural analysis and examination of the reaction with adsorption inhibitors suggest that the reactive substrates may bind non-covalently to specific positions in the confined space of the MMF, thereby inhibiting the over-isomerization reaction. The nanospaces of the MMF with substrate binding ability are expected to enable highly selective synthesis of a variety of terpene compounds.

A porous metal–macrocycle framework (MMF) equipped with a Brønsted acid catalyst in nanochannels enables highly selective isomerization of limonene to terpinolene by kinetically suppressing over-isomerization at confined acid sites.

Cobalt-Catalyzed Remote Hydroboration of Alkenyl Amines

We here present a generally applicable cobalt-catalyzed remote hydroboration of alkenyl amines, providing a practical strategy for the preparation of borylamines and aminoalcohols. This method shows broad substrate scope and good functional group tolerance, tolerating a series of alkenyl amines, including alkyl-alkyl amines, alkyl-aryl amines, aryl-aryl amines, and amides. Of note, this protocol is also compatible with a variety of natural products and drug derivatives. Preliminary mechanistic studies suggest that this transformation involves an iterative chain walking and hydroboration sequence.

One-Pot Synthesis of α-Alkyl Styrene Derivatives

There is a significant need to develop more rapid and efficient routes to styrene derivatives, since they are extensively used in polymer sciences. This manuscript reports a one-pot synthesis of an array of α-alkyl styrene derivatives from readily available natural products (i.e., estragole and safrole). This method is regioselective, producing a rearranged adduct, under transition metal-free conditions. This methodology has broad nucleophile scope, even tolerating sterically hindered nucleophiles; it is general for carbon, nitrogen, oxygen, and sulfur nucleophiles.

Cobalt-Catalyzed Isomerization of Alkenes

Catalytic isomerization of alkenes is a highly atom-economical approach to upgrade from lower- to higher-value alkenes. Consequently, tremendous attention has been devoted to the development of this transformation, approaches which exploit cobalt catalysis are particularly attractive. This short review focuses on the cobalt-catalyzed alkene isomerization, including positional isomerization, geometric isomerization, and cycloisomerization. Three main types of reaction mechanism have been discussed to help the reader to better understand and make meaningful comparison between the different transformations.

1 Introduction

2 Positional Isomerization

3 Geometric Isomerization

4 Cycloisomerization

5 Conclusion and Outlook

Pd-Catalyzed Tandem Isomerization/Cyclization for the Synthesis of Aromatic Oxazaheterocycles and Pyrido[3,4-b]indoles

An effient tandem process consisting of palladium-catalyzed double-bond isomerization of long-chain olefins and subsequent intramolecular cyclization promoted by B₂(OH)₂ for the synthesis of aromatic oxazaheterocycles is disclosed. This strategy can also provide rapid access to pyrido[3,4-b]indoles, trans-2-olefins, and eneamides bearing various functional groups with high regio- and stereoselectivity.

Asymmetric Catalytic Approach to Multilayer 3D Chirality

The first asymmetric catalytic approach to multilayer 3D chirality has been achieved by using Suzuki-Miyaura cross-couplings. New chiral catalysts were designed and screened under various catalytic systems that proved chiral amide-phosphines to be more efficient ligands than other candidates. The multilayer 3D framework was unambiguously determined by X-ray structural analysis showing a parallel pattern of three layers consisting of top, middle and bottom aromatic rings. The X-ray structure of a catalyst complex, dichloride complex of Pd-phosphine amide, was obtained revealing an interesting asymmetric environment nearby the Pd metal center. Three rings of multilayer 3D products can be readily changed by varying aromatic ring-anchored starting materials. The resulting multilayer products displayed strong luminescence under UV irradiation and strong aggregation-induced emission (AIE). In the future, this work would benefit not only the field of asymmetric synthesis but also materials science, in particular polarized organic electronics, optoelectronics and photovoltaics.

Catalytic radical cascade cyclization of alkene-tethered enones to fused bicyclic cyclopropanols

Fused bicyclic cyclopropanols were achieved via an unprecedented HAT-triggered radical cascade reaction of alkene-tethered enones in the presence of an iron catalyst.

Cobalt- and iron-catalyzed regiodivergent alkene hydrosilylations

Regiodivergent olefin hydrosilylation products are accessed through a simple change in the metal center. Linear products (anti-Markovnikov) are obtained using cobalt-based catalysts whereas branched (Markovnikov) products result from an iron-based analogue.