Internal Alkenes Research Articles

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.

Efficient and stable NiMo alloy nanoparticles on ZSM-5 for alkene hydrosilylation

The hydrosilylation of alkene substrates bearing additional functionalities is difficult to achieve by heterogeneous non-noble catalysts and has not been extensively realized with heterogeneous earth-abundant transition metals. Herein, we report NiMo alloy nanoparticles (NPs) supported on ZSM-5 zeolite, which exhibits high activity and selectivity for the hydrosilylation of functionalized terminal and internal alkenes. Compared with the corresponding monometallic counterparts, the Ni3Mo/ZSM-5 catalyst shows a distinct enhancement in the hydrosilylation of alkene. The key to the catalytic performance is the formation of the NiMo alloy, where the electrons are transferred from Mo to Ni. The NiMo alloy NPs have been verified by XRD, XPS and TEM analysis, and further characterized by ICP, BET, NH3-TPD, and H2-TPR. In addition, the Ni3Mo/ZSM-5 catalyst exhibits good reusability for the hydrosilylation reaction with wide substrate scope.

A green Heck reaction protocol towards trisubstituted alkenes, versatile pharmaceutical intermediates.

The Heck reaction is widely employed to build a variety of biologically relevant scaffolds and has been successfully implemented in the production of active pharmaceutical ingredients (APIs). Typically, the reaction with terminal alkenes gives high yields and stereoselectivity toward the trans-substituted alkenes product, and many green variants of the original protocol have been developed for such substrates. However, these methodologies may not be applied with the same efficiency to reactions with challenging substrates, such as internal olefins, providing trisubstituted alkenes. In the present work, we have implemented a Heck reaction protocol under green conditions to access trisubstituted alkenes as final products or key intermediates of pharmaceutical interest. A set of preliminary experiments performed on a model reaction led to selecting a simple and green setup based on a design of experiments (DoE) study. In such a way, the best experimental conditions (catalyst loading, equivalents of alkene, base and tetraalkylammonium salt, composition, and amount of solvent) have been identified. Then, a second set of experiments were performed, bringing the reaction to completion and considering additional factors. The protocol thus defined involves using EtOH as the solvent, microwave (mw) irradiation to achieve short reaction times, and the supported catalyst Pd EnCat®40, which affords an easier recovery and reuse. These conditions were tested on different aryl bromides and internal olefines to evaluate the substrate scope. Furthermore, with the aim to limit as much as possible the production of waste, a simple isomerization procedure was developed to convert the isomeric byproducts into the desired conjugated E alkene, which is also the thermodynamically favoured product. The approach herein disclosed represents a green, efficient, and easy-to-use handle towards different trisubstituted alkenes via the Heck reaction.

Enantioselective Aminosilylation of Alkenes by Palladium/Ming-Phos-Catalyzed Tandem Narasaka-Heck/Silylation Reaction.

A Pd-catalyzed enantioselective aminosilylation of alkenes via tandem Aza-Heck/silylation reaction under Pd/Sadphos catalysis is disclosed. A wide array of oxime esters and silicon reagents are tolerated, furnishing the chiral pyrrolines bearing one quaternary or two contiguous stereocenters in good yield with high enantioselectivity. Not only terminal alkenes but also tri-substituented internal alkenes successfully participate in the reaction, delivering vicinal stereocenters in complete diastereoselectivity and high enantioselectivity. DFT study is conducted to probe the reaction pathway and the origin of the enantioselectivity, which revealed that the stereoinduction arises from the weak interaction between the aromatic ring of the substrate fragment and naphthyl group in the ligand.

Redox Engineering of Myoglobin by Cofactor Substitution to Enhance Cyclopropanation Reactivity.

Design of metal cofactor ligands is essential for controlling the reactivity of metalloenzymes. We investigated a carbene transfer reaction catalyzed by myoglobins containing iron porphyrin cofactors with one and two trifluoromethyl groups at peripheral sites (FePorCF3 and FePor(CF3)2, respectively), native heme and iron porphycene (FePc). These four myoglobins show a wide range of Fe(II)/Fe(III) redox potentials in the protein of +147 mV, +87 mV, +42 mV and -198 mV vs. NHE, respectively. Myoglobin reconstituted with FePor(CF3)2 has a more positive potential, which enhances the reactivity of a carbene intermediate with alkenes, and demonstrates superior cyclopropanation of inert alkenes, such as aliphatic and internal alkenes. In contrast, engineered myoglobin reconstituted with FePc has a more negative redox potential, which accelerates the formation of the intermediate, but has low reactivity for inert alkenes. Mechanistic studies indicate that myoglobin with FePor(CF3)2 generates an undetectable active intermediate with a radical character. In contrast, this reaction catalyzed by myoglobin with FePc includes a detectable iron-carbene species with electrophilic character. This finding highlights the importance of redox-focused design of the iron porphyrinoid cofactor in hemoproteins to tune the reactivity of the carbene transfer reaction.

Redox Engineering of Myoglobin by Cofactor Substitution to Enhance Cyclopropanation Reactivity

AbstractDesign of metal cofactor ligands is essential for controlling the reactivity of metalloenzymes. We investigated a carbene transfer reaction catalyzed by myoglobins containing iron porphyrin cofactors with one and two trifluoromethyl groups at peripheral sites (FePorCF3 and FePor(CF3)2, respectively), native heme and iron porphycene (FePc). These four myoglobins show a wide range of Fe(II)/Fe(III) redox potentials in the protein of +147 mV, +87 mV, +42 mV and −198 mV vs. NHE, respectively. Myoglobin reconstituted with FePor(CF3)2 has a more positive potential, which enhances the reactivity of a carbene intermediate with alkenes, and demonstrates superior cyclopropanation of inert alkenes, such as aliphatic and internal alkenes. In contrast, engineered myoglobin reconstituted with FePc has a more negative redox potential, which accelerates the formation of the intermediate, but has low reactivity for inert alkenes. Mechanistic studies indicate that myoglobin with FePor(CF3)2 generates an undetectable active intermediate with a radical character. In contrast, this reaction catalyzed by myoglobin with FePc includes a detectable iron–carbene species with electrophilic character. This finding highlights the importance of redox‐focused design of the iron porphyrinoid cofactor in hemoproteins to tune the reactivity of the carbene transfer reaction.

Asymmetric 1,n‐Remote Aminoacetoxylation of Unactivated Internal Alkenes Enabled by Palladium Catalysis**

AbstractA palladium‐catalyzed asymmetric 1,n‐remote aminoacetoxylation of cis‐alkenes has been developed using PhI(OAc)2 as an oxidant, providing the acetoxylated lactams with excellent enantioselectivities under mild reaction conditions. The sterically hindered pyridine‐oxazoline (Pyox) L3 with a tert‐butyl group in oxazoline ring and propyl group in C6 position of pyridinyl is vital for the reaction, where the former is good for asymmetric aminopalladation step and the latter for the chain walking process. The enantioenriched lactam products were proven to be good building blocks for the synthesis of azabicycles.

Asymmetric 1,n-Remote Aminoacetoxylation of Unactivated Internal Alkenes Enabled by Palladium Catalysis.

A palladium-catalyzed asymmetric 1,n-remote aminoacetoxylation of cis-alkenes has been developed using PhI(OAc)2 as an oxidant, providing the acetoxylated lactams with excellent enantioselectivities under mild reaction conditions. The sterically hindered pyridine-oxazoline (Pyox) L3 with a tert-butyl group in oxazoline ring and propyl group in C6 position of pyridinyl is vital for the reaction, where the former is good for asymmetric aminopalladation step and the latter for the chain walking process. The enantioenriched lactam products were proven to be good building blocks for the synthesis of azabicycles.

Regio- and enantioselective hydrofluorination of internal alkenes via nickel-catalyzed hydrogen atom transfer

Regio- and enantioselective hydrofluorination of internal alkenes via nickel-catalyzed hydrogen atom transfer

General Regio- and Diastereoselective Allylic C-H Oxygenation of Internal Alkenes.

Branched allylic esters and carboxylates are fundamental motifs prevalent in natural products and drug molecules. The direct allylic C-H oxygenation of internal alkenes represents one of the most straightforward approaches, bypassing the requirement for an allylic leaving group as in the classical Tsuji-Trost reaction. However, current methods suffer from limited scope─often accompanied by selectivity issues─thus hampering further development. Herein we report a photocatalytic platform as a general solution to these problems, enabling the coupling of diverse internal alkenes with carboxylic acids, alcohols, and other O-nucleophiles, typically in a highly regio- and diastereoselective manner.

α-Bromoacetate as a Mild and Safe Brominating Agent in the Light-Driven Vicinal Dibromination of Unactivated Alkenes and Alkynes.

Light-induced vicinal dibromination of unactivated alkenes and alkynes has been demonstrated by using methyl α-bromoacetate as a mild brominating agent. A near-visible light (370 nm) light-emitting diode (LED) mediates this simple dibromination reaction under mild conditions with the inexpensive and nontoxic α-bromoacetate. The reaction proceeds well with both terminal and internal alkenes and alkynes and those contained in N/O-heterocycles, indicating its versatility in synthesizing dibrominated organic compounds.

Electrochemical Allylic C(sp3)-H Isothiocyanation via [3,3]-Sigmatropic Rearrangement.

The direct allylic C(sp3)-H functionalization provides a straightforward protocol for the synthesis of valuable molecules. We report herein the first chemo- and site-selective method for allylic C(sp3)-H isothiocyanation of various internal alkenes under mild electrochemical conditions. This method exhibits broad functional group tolerance and excellent selectivity and can be applied for late-stage isothiocyanation of bioactive molecules. Combined experimental and computational studies indicate that the reaction proceeds via an unexpected [3,3]-sigmatropic rearrangement.

Hydroformylation of Olefins with CO2/H2 and Hydrosilane by Copper/Cobalt Tandem Catalysis.

A Cu/Co tandem catalysis protocol was developed to conduct the hydroformylation of olefins using CO2/H2 and PMHS (polymethylhydrosiloxane) as a readily available and environmentally friendly hydride source. This methodology was performed via a two-step approach consisting of the copper-catalyzed reduction of CO2 by hydrosilane and subsequent cobalt-promoted hydroformylation with H2 and the in situ formed CO. The optimized triphos oxide ligand, which presumably facilitates the migratory insertion of CO gives moderate to excellent yields for both terminal and internal alkenes. This earth-abundant metal catalysis provides a reliable and efficient way to afford useful aldehydes in industry using silicon by-product PMHS as hydrogen source and renewable CO2 as carbonyl source.

STUDY OF THE DYNAMICS OF THE PROCESS OF ADSORPTION OF AROMATIC HYDROCARBONS FROM ALKANE

In petrochemistry, normal paraffins are used mainly as raw materials for the production of alkylbenzenes, alkanesulfonates, synthetic fatty acids, secondary alcohols, a-olefins (thermocracking), internal olefins (dehydrogenation). Currently, the market for synthetic detergents (SMC) is one of the most dynamically developing in the world. According to the forecasts of the leading companies producing alkyl benzenes, in the next 10 years, the demand for intermediates for the production of synthetic detergents is expected to grow both in domestic markets and in the global market as a whole. At hydrotreatment units, a wide fraction of n-paraffins (C9–C20) is released from hydrotreated diesel fuel. After that, the C9–C20 fraction is sent to the pre-fractionation unit of the olefin production unit, where the C14–C17 fraction is separated from the wide fraction. This fraction is marketable and requires preliminary purification from aromatic hydrocarbons. Typically, the content of aromatic hydrocarbons in the crude fraction С14+ is from 0.5 to 2.0 wt%. The residual content of aromatic hydrocarbons in the purified fraction should not exceed 0.01% wt. To remove aromatic hydrocarbons, the С14+ fraction is fed to the oleum treatment unit. At the oleum purification unit, post-treatment is carried out using oleum with a concentration of 20–24% wt. After sulfonation, it is necessary to neutralize with caustic soda. Obtaining dearomatized liquid paraffins from diesel fuel using oleum purification has many disadvantages, since working with fuming sulfuric acid requires a high degree of protection of the human body and the strictest observance of safety regulations. Due to the difficulties in disposing of spent sulfuric acid, plant shutdowns and downtime are not uncommon. This article presents the results of a comprehensive study of the adsorption of aromatic hydrocarbons from higher alkanes on zeolite CaX. The main parameters of statics, dynamics and kinetics of adsorption are determined

Palladium-Catalyzed Remote Hydrosulfonamidation of Alkenes: Access to Primary N-Alkyl Sulfamides by the SuFEx Reaction.

Herein, we establish a remote hydrosulfonamidation (HSA) of alkenes using palladium catalysis, where N-fluoro-N-(fluoro-sulfonyl)-carbamate with a sulfur(VI) fluoride moiety is demonstrated as a good amidation reagent. The anti-Markovnikov HSA reaction of terminal alkenes and the remote HSA of internal alkenes are achieved to efficiently yield primary N-alkyl-N-(fluorosulfonyl)-carbamates. In addition, this protocol enables the high-value utilization of alkane by combining the dehydrogenation process. The generated N-alkyl products exhibit a unique reactivity of sulfur(VI) fluorides, which can be directly transferred to N-alkyl sulfamides or amines via the sulfur(VI) fluoride exchange reaction, thereby streamlining their synthesis. Moreover, a (pyridyl) benzazole-type ligand proved to be vital for the excellent chemo- and regioselectivities.

Stereospecific syn-dihalogenations and regiodivergent syn-interhalogenation of alkenes via vicinal double electrophilic activation strategy

Whereas the conventional anti-dihalogenation of alkenes is a valuable synthetic tool with highly predictable stereospecificity, the restricted reaction mechanism makes it challenging to alter the diastereochemical course into the complementary syn-dihalogenation process. Only a few notable achievements were made recently by inverting one of the stereocenters after anti-addition using a carefully designed reagent system. Here, we report a conceptually distinctive strategy for the simultaneous double electrophilic activation of the two alkene carbons from the same side. Then, the resulting vicinal leaving groups can be displaced iteratively by nucleophilic halides to complete the syn-dihalogenation. For this purpose, thianthrenium dication is employed, and all possible combinations of chlorine and bromine are added onto internal alkenes successfully, particularly resulting in the syn-dibromination and the regiodivergent syn-bromochlorination.

Accessing Cyclobutane Polymers: Overcoming Synthetic Challenges via Efficient Continuous Flow [2 + 2] Photopolymerization.

We report an improved and efficient method to prepare well-defined, structurally complex truxinate cyclobutane polymers via a thioxanthone sensitized solution state [2 + 2] photopolymerization. Monomers with varying electron density and structure polymerize in good to excellent yields to afford a library of 42 polyesters. Monomers with internal olefin separation distances of greater than 5 Å undergo polymerization via intermolecular [2 + 2] photocycloaddition readily, as opposed to the intramolecular [2 + 2] photocycloaddition observed in monomers with olefins in closer proximity. Use of a continuous flow reactor decreases reaction time, increases polymer molecular weight, and decreases dispersity compared to batch reactions. Furthermore, under continuous flow, polymerization is readily scalable beyond what is possible with batch reactions. This advancement ushers truxinate cyclobutane-based polyesters, which have been historically limited to a few examples and only research scale quantities, to the forefront of development as new materials for potential use across industry sectors.

Ni-Catalyzed Diastereoconvergent Intramolecular Alkene-Aldehyde Reductive Coupling: A Route to syn-Chromanols.

We demonstrate for the first time a nickel-catalyzed diastereoconvergent reductive coupling of a heteroatom-attached allyl moiety with aldehydes, viz., O-allyl, O-cinnamyl salicylaldehydes, and others, to afford syn-chromanols exclusively. The reaction proceeds through a [2 + 2 + 1] oxidative cycloaddition involving the active catalyst. This method is applicable to both terminal and internal olefin substrates. The formal syntheses of CP-199.330, CP-199.331, and CP-85.958 have been demonstrated. Control experiments, mass spectrometric analysis, and DFT studies supported the plausible mechanism and the origin of exclusive syn-selectivity.

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.

Stereodivergent, Kinetically Controlled Isomerization of Terminal Alkenes via Nickel Catalysis

AbstractBecause 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.