Internal Alkenes Research Articles

Photoinduced Pd‐Catalyzed Direct Sulfonylation of Allylic C−H Bonds

AbstractAllylic sulfones are valuable motifs due to their medicinal and biological significance and their versatile chemical reactivities. While direct allylic C−H sulfonylation represents a straightforward and desirable approach, these methods are primarily restricted to terminal alkenes, leaving the engagement of the internal counterparts a formidable challenge. Herein we report a photocatalytic approach that accommodates both cyclic and acyclic internal alkenes with diverse substitution patterns and electronic properties. Importantly, the obtained allylic sulfones can be readily diversified into a wide range of products, thus enabling formal alkene transposition and all‐carbon quaternary center formation through the sequential C−H functionalization.

Pd-Catalyzed highly regioselective migratory hydroesterification of internal olefins with formates

Double bonds of internal olefins can be efficiently migrated to the terminal carbons and regioselectively hydroesterified with formates in the presence of Pd(OAc)2 and 1,2-DTBPMB under mild reaction conditions, providing a wide variety of corresponding linear carboxylic esters bearing various functional groups in good yields and >20:1 linear/branch ratios. The reaction is optionally simple and does not need to use CO gas and acid co-catalysts.

Enantioselective Intramolecular Oxidative Aminoacetoxylation from Aryl-Substituted Alkene via Chiral Triazole-oxazoline Palladium Complexes.

Here, we describe an enantioselective intramolecular oxidative aminoacetoxylation reaction using a palladium catalyst and an aryl-substituted internal alkene compound as the substrate under mild conditions in several hours. The triazole-oxazoline ligand was selected for the asymmetric catalyst. A range of enantioenriched pyrrolidine-derived vicinal amino acetate compounds were synthesized, showing yields from 47% to 84%, diastereomer ratios from 57:43 to 95:5, and enantiomer excesses from 67% to 92%.

Remote Catalytic C(sp3)-H Alkylation via Relayed Carbenoid Transfer upon Olefin Chain Walking.

Transition metal carbenes have emerged as versatile intermediates for various types of alkylations. While reactions of metal carbene species with alkenes have been extensively studied, most examples focus on cyclopropanation and allylic C-H insertion. Herein, we present the first example of a catalytic strategy for the carbene-involved regioselective remote C-H alkylation of internal olefins by synergistically combining two iridium-mediated reactivities of olefin chain walking and carbenoid migratory insertion. The present method, utilizing sulfoxonium ylides as a bench-stable robust carbene precursor, was found to be effective for a series of olefins tethered with alkyl chains, heteroatom substituents, and complex biorelevant moieties. Combined experimental and computational studies revealed that reversible iridium hydride-mediated olefin chain walking proceeds to lead to a terminal alkyl-Ir intermediate, which then forms a carbenoid species for the final migratory insertion, resulting in regioselective terminal-alkylated products.

Stereospecific 3-Aza-Cope Rearrangement Interrupted Asymmetric Allylic Substitution-Isomerization.

Transition-metal catalyzed asymmetric allylic substitution with alkyl and heteroaryl carbon nucleophiles has been well-established. However, the asymmetric allylic arylation of acyclic internal alkenes with aryl nucleophiles remains challenging and underdeveloped. Herein we report a stereospecific 3-aza-Cope rearrangement interrupted asymmetric allylic substitution-isomerization (Int-AASI) that enables asymmetric allylic arylation. By means of this stepwise strategy, both enantioenriched allylic arylation products and axially chiral alkenes could be readily obtained in high enantioselectivities. Experimental studies support a mechanism involving a cascade of asymmetric allylic amination, stereospecific aryl 3-aza-Cope rearrangement and alkene isomerization. Density functional theory studies detailed the reasons of achieving the high chemoselectivity, regioselectivity, stereoselectivity and stereospecificity, respectively.

Rare-Earth Metal-Catalyzed Regioselective Hydrosilylation of Internal Alkenes and Alkynes

A highly regioselective hydrosilylation reaction of internal alkenes was achieved by commercially available La(HMDS)3. Notably, the Z or E configuration of internal alkenes displays negligible influence on the reactivity and regioselectivity. In addition, internal alkynes were applicable, affording the mono di-hydrosilylation product in the presence of La(HMDS)3 or mono-hydrosilylation product with Y(HMDS)3 as the promoter.

An Expedient Route to Bio‐based Polyacrylate Alternatives with Inherent Degradation Capabilities by Organic Catalysis for Polymerization of Muconate Esters

The quest for polymers that would be at the same time bio‐based and degradable after usage, in addition to offering chemical post‐modification options, remains a daunting challenge in contemporary polymer science. Despite advances in polymer chemistry, attempts at controlling the chain‐growth polymerization of muconate esters remain unexplored. Here we show that dialkyl muconates can be rapidly polymerized by organocatalyzed group transfer polymerization (O‐GTP). O‐GTP is conducted to completion at room temperature in toluene within a few minutes, using 1‐ethoxy‐1‐(trimethylsiloxy)‐1,3‐butadiene (ETSB) as initiator and 1‐tert‐butyl‐4,4,4‐tris(dimethylamino)‐2,2‐bis[tris(dimethylamino)‐phosphoranylidenamino]‐25,45 catenadi(phosphazene) (P4‐t­‐Bu) as catalyst. Chain extension experiments and synthesis of all muconate‐type block copolymers can also be achieved. Furthermore, polymuconates are amenable to facile post‐polymerization modification reactions. This is showcased through the hydrolysis of the ester side chains leading to well‐defined poly(muconic acid), and by epoxidation of the C=C double bonds of the main chain. Last but not least, these internal alkene groups can be selectively cleaved by ozonolysis, demonstrating the upcyclability of polymuconates under oxidative conditions. This work demonstrates that polymuconates constitute a unique platform of bio‐based polymers, easily modifiable in addition to being chemically degradable under user friendly experimental conditions.

An Expedient Route to Bio-Based Polyacrylate Alternatives with Inherent Post-Chemical Modification and Degradation Capabilities by Organic Catalysis for Polymerization of Muconate Esters.

The quest for polymers that would be at the same time bio-based and degradable after usage, in addition to offering chemical post-modification options, remains a daunting challenge in contemporary polymer science. Despite advances in polymer chemistry, attempts at controlling the chain-growth polymerization of muconate esters remain unexplored. Here we show that dialkyl muconates can be rapidly polymerized by organocatalyzed group transfer polymerization (O-GTP). O-GTP is conducted to completion at room temperature in toluene within a few minutes, using 1-ethoxy-1-(trimethylsiloxy)-1,3-butadiene (ETSB) as initiator and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2 5,4 5 catenadi(phosphazene) (P4-t-Bu) as catalyst. Chain extension experiments and synthesis of all muconate-type block copolymers can also be achieved. Furthermore, polymuconates are amenable to facile post-polymerization modification reactions. This is showcased through the hydrolysis of the ester side chains leading to well-defined poly(muconic acid), and by epoxidation of the C=C double bonds of the main chain. Last but not least, these internal alkene groups can be selectively cleaved by ozonolysis, demonstrating the upcyclability of polymuconates under oxidative conditions. This work demonstrates that polymuconates constitute a unique platform of bio-based polymers, easily modifiable in addition to being chemically degradable under user friendly experimental conditions.

Photoinduced Pd-Catalyzed Direct Sulfonylation of Allylic C-H Bonds.

Allylic sulfones are valuable motifs due to their medicinal and biological significance and their versatile chemical reactivities. While direct allylic C-H sulfonylation represents a straightforward and desirable approach, these methods are primarily restricted to terminal alkenes, leaving the engagement of the internal counterparts a formidable challenge. Herein we report a photocatalytic approach that accommodates both cyclic and acyclic internal alkenes with diverse substitution patterns and electronic properties. Importantly, the obtained allylic sulfones can be readily diversified into a wide range of products, thus enabling formal alkene transposition and all-carbon quaternary center formation through the sequential C-H functionalization.

Defluorinative Haloalkylation of Unactivated Alkenes Enabled by Dual Photoredox and Copper Catalysis.

A three-component defluorinative haloalkylation of alkenes with trifluoromethyl compounds and TBAX (X = Cl, Br) via dual photoredox/copper catalysis is reported. The mild conditions are compatible with a wide array of activated trifluoromethyl aromatics bearing diverse substituents, and various nonactivated terminal and internal alkenes, enabling straightforward access to synthetically valuable γ-gem-difluoroalkyl halides with high efficiency. Mechanistic studies indicate that the [Cu] complexes not only serve as XAT catalysts but also facilitate the SET reduction of trifluoromethyl groups by photocatalysts. Additionally, the resulting alkyl halide products can serve as versatile conversion intermediates for the synthesis of a diverse range of γ-gem-difluoroalkyl compounds.

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.

Anti-selective Cyclopropanation of Nonconjugated Alkenes with Diverse Pronucleophiles via Directed Nucleopalladation.

A facile approach to obtaining densely functionalized cyclopropanes is described. The reaction proceeds under mild conditions via the directed nucleopalladation of nonconjugated alkenes with readily available pronucleophiles and gives excellent yields and good anti-selectivity using I2 and TBHP as oxidants. Pronucleophiles bearing a diverse collection of electron-withdrawing groups, including -CN, -CO2R, -COR, -SO2Ph, -CONHR, and -NO2, are well tolerated. Internal alkenes, which are generally challenging substrates in other cyclopropanation methods, provide excellent yields and good diastereoselectivity in this methodology, allowing for controlled access to cyclopropanes substituted at all three C atoms. DFT calculations and mechanistic experiments reveal that the major mechanistic pathway involves the initial α-iodination of the nucleophile, followed by anti-carbopalladation and intramolecular C(sp3)-I oxidative addition. Strain-release-promoted C(sp3)-C(sp3) reductive elimination then furnishes the cyclopropanated product.

Copper-Catalyzed Asymmetric Hydroaminocarbonylation of Unactivated Internal Alkenes

Copper-Catalyzed Asymmetric Hydroaminocarbonylation of Unactivated Internal Alkenes

Synthesis and Characterization of Transition Metal Complexes Supported by Phosphorus Ligands Obtained Using Hydrophosphination of Cyclic Internal Alkenes.

The design and study of rich, bulky phosphorus ligands is a key area of research for homogeneous catalysis. Here, we describe an original strategy using a hydrophosphination reaction to produce phosphines of interest for coordination chemistry and homogenous catalysis. In particular, the phosphine obtained by reacting diphenylphosphine with acenaphthylene (ligand 2) gives a ligand that adopts an unusual spatial geometry. The coordination chemistry of the ligand has been investigated with Au(I), Ag(I), Cu(I), and Pd(II), for which a complete characterization could be made, particularly in X-ray diffraction studies. The reactivity of some of these complexes has been demonstrated, particularly in Pd-catalyzed cross-coupling reactions and Au-catalyzed hydroaminations and in the hydration of alkynes.

A highly active phosphine oxides-containing porous organic polymer supported Co catalyst for hydroformylation of 2-octene

The development of earth-abundant catalysts with high activity and selectivity is important yet challenging in hydroformylation. In this work, a stable and efficient phosphine-oxide group containing porous organic polymer was afforded, which served as a ligand and a support to fabricate a heterogeneous Co catalyst (Co/POL-POPh3) for hydroformylation of 2-octene under mild condition. A 2-octene conversion of 94.6 % and at least three recycles were achieved using Co/POL-POPh3 in the hydroformylation with a 51.1 % aldehyde selectivity under 423 K and 3.0 MPa. The experimental and characterization results elucidated that the highly dispersed Co ions was coordinated with the phosphine-oxide groups in the polymer, which was beneficial for the 2-octene isomerization and in turn led to the excellent performance for synthesis of oxygenates. Furthermore, a reaction mechanism was also suggested for 2-octene hydroformylation over the Co/POL-POPh3 catalyst. The current study delivers valuable insights into the adjustment of the catalytic efficiency of non-previous metal catalysts in the heterogeneous hydroformylation of internal olefins.

Alkene Isomerisation Catalysed by a Superbasic Sodium Amide

AbstractTypically catalysed by transition metals, alkene isomerisation is a powerful methodology for preparation of internal olefins. In contrast, the use of more earth abundant main group reagents is limited to activated substrates, requiring high temperatures and excess stoichiometric amounts. Opening a new avenue for progressing this field, here we report applications of bulky sodium amide NaTMP (TMP=2,2,6,6‐tetramethylpiperidide) when partnered with tridentate Lewis donor PMDETA (N,N,N′,N′′,N’’‐pentamethyldiethylenetriamine) in catalytic alkene isomerisation of terminal olefins under mild reaction conditions. An array of distinct olefins could successfully be isomerised, including unactivated olefins, allylamines, and allylethers, showing the high activity of this partnership. In‐depth mechanistic insights provided by X‐ray crystallography, real‐time nuclear magnetic resonance (NMR) monitoring, and density functional theory (DFT) calculations have unveiled the crucial role of in situ‐generated TMP(H) in facilitating efficient isomerisation, and the choice of alkali‐metal. Additionally, theoretical studies shed light on the observed E/Z selectivity, particularly accounting for the selective formation of Z‐vinyl ethers. The versatility of our method is further demonstrated through the isomerisation of unactivated cycloalkenes, which undergo hydrogen isotope exchange to produce deuterated compounds.

Unconventional Ligand‐to‐Catalyst Ratio for the Distal C−C Bond Formation via C−H Activation and Chain‐Walking

AbstractA mechanism‐navigated enantioselective alkylation of an indole C2 C−H bond with an internal alkene was developed. Under the unconventional ligand‐to‐metal catalyst ratio, a moderate enantiomeric ratio (er), ranging from 70:30 to 88:12, was achieved with our original ligand. We propose that chain‐walking and bond formation are mechanistically independent and suggest that hydridoiridium generated from the C−H source does not play a role in the chain‐walking process.

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.

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.