Olefin Isomerization Research Articles

Enantioselective Synthesis of α-Hydroxy Allyl Ketones via BINAP-CuH-Catalyzed Hydroacylation.

Catalytic hydrocupration of unsaturated carbon-carbon bonds to generate organometallic nucleophiles has recently become an attractive alternative to conventional stoichiometric reagents in the stereoselective synthesis. Herein, we have developed an efficient and economical method to synthesize enantiopure α-hydroxy allyl ketones via a copper hydride (CuH)-catalyzed hydroacylation of alkoxyallenes, a significant advancement given the scarcity of reports on such scaffolds in the literature. DFT calculations reveal that this reaction proceeds through the nucleophilic attack of a kinetically favourable Z-selective allyl-copper intermediate on acid anhydrides via a six-membered chair-like transition state, stabilized by strongly attractive non-covalent interactions that ultimately leads to high level of enantioselectivities using the simple BINAP ligand. This method successfully overcomes the challenges of over-reduction of carbonyl functionality in the presence of CuH-complex, olefin isomerization and the presence of a highly enolizable α-stereocenter, which can lead to erosion in enantioselectivities, making our strategy highly desirable. The reaction exhibits a wide range of substrate scope including symmetrical as well as carbonic anhydrides with both aromatic, and aliphatic substitutions. In addition, α-substituted acid anhydrides provide exclusive syn-selective α,α'-disubstituted allyl ketones in excellent enantiomeric ratios, where the nucleophilic allylation occurs on one of the carbonyls containing the matched α-stereocenter, confirmed with mechanistic studies.

An open-shell Ir(II)/Ir(IV) redox couple outperforms an Ir(I)/Ir(III) pair in olefin isomerization.

Open-shell systems based on first-row transition metals and their involvement in various catalytic processes are well explored. By comparison, mononuclear open-shell complexes of precious transition metals remain underdeveloped. This is particularly true for IrII complexes, as there is very limited information available regarding their application in catalysis. Here we show that a family of IrII metalloradicals, featuring a C6H3-2,6-(OP(tBu)2)2 (POCOP) pincer ligand, effectively catalyses olefin isomerization-a key step in alkane metathesis-exhibiting up to 20 times higher activity than their IrI counterparts. Computational studies reveal that the IrII/IrIV redox cycling enables faster kinetics than the traditional IrI/IrIII pathway owing to reduced barriers for the oxidative addition and reductive elimination steps. Thus, this study presents a redox catalyst involving an IrII/IrIV pair, highlighting the capabilites of precious-metal systems that extend beyond traditional redox cycles. These findings emphasize the need for expanding catalytic design principles, especially for platinum-group metals.

Iterative synthesis of stereodefined polyacetals and their domino-Coates-Claisen rearrangement.

We report a fully stereocontrolled synthesis of previously unknown unsaturated polyacetals through an iteration of two steps: (1) Pd-catalyzed hydroalkoxylation of alkoxyallenes; and (2) base-mediated isomerization of propargyl ethers into alkoxyallenes. Site- and stereoselective alkene isomerization of the capping allyl group initiates a domino-Coates-Claisen rearrangement, which completely rearranges the iteratively assembled backbone with the stereochemistry of the newly formed stereocentres controlled by the configuration of the acetal centres in the starting materials. The resulting products feature multiple stereocentres in a 1,3-relationship, which map onto a broad range of bioactive natural products, including deoxypropionates.

Borenium-Catalyzed "Boron Walking" for Remote Site-Selective Hydroboration.

Remote functionalization through progressive olefin isomerization enables site-selective modification at a distal position, diversifying the synthetic approaches. However, the developed protocols have long relied on transition metal catalysis. Transition metal catalysts are deemed irreplaceable, albeit facing challenges in metal residue and catalyst poisoning. In this work, we present a pioneering approach that employs a borenium ion as a catalyst for site-selective, remote borylation, eliminating the need for metal catalysts. As the reaction progresses, borylation isomers at different positions emerge, gradually and ultimately converging into the predominant α-borylation product. This process is akin to a "walking" of a boron moiety along a carbon skeleton toward an aryl terminus. Detailed mechanistic studies and DFT calculations substantiate the borenium-catalyzed, stepwise migration via a reversible B-H insertion/elimination sequence. This remote borylation exhibits good functional group compatibility, complementing those methods reliant on transition metals. Furthermore, this metal-free protocol permits the convenient synthesis of silyl-remote-boryl compounds, demonstrating an opposite regioselectivity to that observed in transition-metal-catalyzed tandem silylation-borylation reactions. This discovery therefore contributes to site-selective, remote difunctionalization via sequential C-B and C-Si derivatizations, exemplified by the synthesis of amino-remote-alcohol bioactive molecules.

Phenanthrolines as Energy Transfer Photocatalysts for the E → Z Isomerization of Alkenes

Phenanthrolines have been widely employed as chelating ligands for transition metals. Herein, this study investigates the utility of substituted o-phenanthrolines as independent photosensitizers for the E → Z isomerization of alkenes. Our findings underscore the versatility of o-phenanthrolines, providing a straightforward, metal-free, and cost-effective method for synthesizing Z-alkenes.

Conversion of Phenols and Anilines to trans-Olefins via Oxidation, Wittig Olefination, and Stereoselective Olefin Isomerization.

Development of metal-free conversion of naturally abundant phenols and anilines to the corresponding olefins remains a formidable challenge. The current state of the art relies on the TM-catalyzed Heck coupling of activated phenols (triflates, tosylates, and more) with the olefins. While these advancements are promising, the reaction suffers from branch vs linear selectivity and requires an expensive TM-ligand combination, hazardous organotin reagents, and very high reaction temperature. Herein, we reported a one-pot conversion of phenol and anilines to the corresponding E-olefins, which goes via oxidation, Wittig olefination, and stereoselective olefin isomerization.

Palladium-catalyzed remote internal C(sp3)−H bond chlorination of alkenes

C(sp3)–Cl bonds are present in numerous biologically active molecules and can also be used as a site for diversification by substitution or cross-coupling reactions. Herein, we report a remote internal site-selective C(sp3)–H bond chlorination of alkenes through sequential alkene isomerization and hydrochlorination, enabling the synthesis of both benzylic and tertiary chlorides with excellent site-selectivity. This transformation offers exciting possibilities for the late-stage chlorination of derivatives of natural products and pharmaceuticals. We also demonstrate the regioconvergent synthesis of a single alkyl chloride from unrefined mixtures of isomeric alkenes, which can be extracted directly from petrochemical sources.

Stereo- and Enantioselective Syntheses of 1,2-Oxaborinan-3-enes and δ-Boryl-Substituted Homoallylic Alcohols.

Stereo- and enantioselective syntheses of 1,2-oxaborinan-3-enes and δ-boryl-substituted homoallylic alcohols are reported. We developed a practical approach to synthesize α-boryl-substituted allylboronate. This reagent was utilized to generate α,α-disubstituted allylboronates, and such reagents cannot be accessed via the Pd-catalyzed alkene isomerization approach. Chiral Brønsted-acid-catalyzed aldehyde addition with these reagents gave 1,2-oxaborinan-3-enes with excellent stereo- and enantioselectivities. Lewis-acid-catalyzed aldehyde addition also worked well, affording δ-boryl-substituted homoallylic alcohols with high stereoselectivities. The enantioselective variant of the reaction was achieved via a chiral Brønsted-acid-catalyzed aldehyde addition and Pd-catalyzed alkene isomerization approach.

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 3-aza-Cope rearrangement and alkene isomerization. Density functional theory studies detailed the reasons of achieving the high chemoselectivity, regioselectivity, stereoselectivity and stereospecificity, respectively.

Stereospecific 3‐Aza‐Cope Rearrangement Interrupted Asymmetric Allylic Substitution‐Isomerization

AbstractTransition‐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 3‐aza‐Cope rearrangement and alkene isomerization. Density functional theory studies detailed the reasons of achieving the high chemoselectivity, regioselectivity, stereoselectivity and stereospecificity, respectively.

Isomerization of alkanes on domestic bentonite

Изучено превращение н-бутана на активированном Кынгракском бентоните, содержащем нанесенный рутений. Совместное присутствие водяного пара с н-бутаном в реакционной зоне уменьшает коксообразование на поверхности катализатора и способствует увеличению выхода изооктана. В данной статье приведены исследования изомеризации н-бутана на рутениевых катализаторах, нанесенных на Кынгракский бентонит, где преобладающим минералом является монтмориллонит. Совместное присутствие водяного пара с н-бутаном в реакционной зоне снижает коксообразование на поверхности катализатора и способствует увеличению выхода изооктана. Изомеризация н-бутана и н-пентана в соответствующий изобутан и изопентан является значимой реакцией в получении алкилбензинов и оксигенатов Қ-бутанның құрамында рутений бар белсендірілген Қынғырақ бентонитіне айналуы зерттелді. Реакция аймағында су буының қ-бутанмен бірге болуы катализатор бетіндегі кокстың түзілуін азайтады және изооктан шығымдылығының артуына ықпал етеді. Бұл мақалада монтмориллонит басым минерал болып табылатын Қынғырақ бентонитіне қолданылатын рутений катализаторларындағы қ-бутанның изомерленуі туралы зерттеулер келтірілген. Реакция аймағында су буының қ-бутанмен бірге болуы катализатор бетіндегі кокстың түзілуін азайтады және изооктан шығымдылығының артуына ықпал етеді. Қ-бутан мен н-пентанның сәйкес изобутан мен изопентанға изомерленуі алкилбензиндер мен оксигенаттарды өндіруде маңызды реакциялар болып табылады The transformation of n-butane on activated Kyngrak bentonite containing deposited ruthenium has been studied. The combined presence of water vapor with n-butane in the reaction zone reduces coke formation on the surface of the catalyst and increases the yield of isooctane. This article presents studies of the isomerization of n-butane on ruthenium catalysts deposited on Kyngrak bentonite, where montmorillonite is the predominant mineral. The combined presence of water vapor with n-butane in the reaction zone reduces coke formation on the surface of the catalyst and increases the yield of isooctane. The isomerization of n-butane and n-pentane into the corresponding isobutane and isopentane are significant reactions in the production of alkylbenzenes and oxygenates

Application of Hydroxyaromatic Aldehydes in Ultra-Efficient and Metal-Free Photocatalytic E→Z Isomerization of Olefin.

The strategy of photocatalyzed E→Z isomerization of olefins to access thermodynamically less stable Z-alkenes has recently received considerable attention. Here, we have discovered a sensitizer of hydroxyaromatic aldehyde that can rapidly achieve olefin E→Z isomerization under blue light irradiation. Notably, 2-hydroxybenzene-1,3,5-tricarbaldehyde, when assisted by blue light, can achieve efficient and selective conversion within just 5 minutes (Z/E=92 : 8). The reaction can be successfully scaled up to gram scale, and exhibits remarkable reactivity toward various derivatives of ethyl cinnamate (27 examples) and other olefins. Furthermore, the former can be directly cyclized by a hydroxyl derivative to produce 4-substituted coumarin. The prominent preponderance of this method includes being metal-free, efficient, convenient, no by-products and achieving high selectivity. Correlation of sensitizer triplet energy (ET) and preliminary mechanistic experiments indicate that the accomplishment of this reaction is based on the selective excitation mechanism.

Tandem Hydrocyanation and Nitrile/Amide Cyclization of Propiolamides: A Rapid Access to 5‐Iminopyrrolones

AbstractA Pd‐catalyzed synthesis of 5‐iminopyrrolones from propiolamides was developed, which featured wide substrate scope and good yields. This efficient conversion involved a tandem hydrocyanation, E to Z isomerization of alkenes, and nitrile/amide cyclization. Control experiments show the intermediacy of β‐cyanation products, and the Z‐isomers was efficiently converted to the target products by Pd/L2 catalysis only after the cyanation reagent was completely consumed.

Hydrodesulfurization and isomerization performance of model FCC naphtha over sulfided Co(Ni)–Mo/Y catalysts

The process of deep hydrodesulfurization (HDS) in gasoline typically results in the saturation of olefins, leading to significant reductions in octane number. In this work, Y-supported Co(Ni)–Mo catalysts that with different Ni–Co content were prepared by the incipient wetness impregnation method, the structure and properties were characterized and analyzed using HRTEM, XPS, H2-TPR, and NH3-TPD. The isomerization of 1-hexene and 1-octene as well as the HDS of thiophene were studied by using model FCC naphtha. The incorporation of Ni was found to enhance the number of MoS2 stacking layers, thereby improving the degree of sulfurization in Mo and subsequently increasing the desulfurization rate, with a maximum achieved desulfurization rate of 94.7%. When employing a Ni/Co ratio of 3:2, optimal synergy between Ni and Co is achieved, resulting in a greater presence of multi-layer stacked II-Co(Ni)MoS active phases. Additionally, appropriate Brønsted acidity levels are maintained to facilitate efficient olefin isomerization while preserving high HDS activity. As a result, the current isomerization yield stands at 58.2%(mass). These understandings shed light on the development of highly HDS and olefin isomerization catalysts.

Oxidative Organic Transformations Photocatalyzed by NDI in Visible Light.

In this work, we report the synthesis and photocatalytic properties of N,N-bis(n-hexyl)-2-bromo-6-(n-hexylamino)-1,4,5,8-naphthalenetetracarboxylic diimide photocatalyst, NDI-PC, in visible light. In the presence of air or oxidant, NDI-PC efficiently enables multiple photooxygenations of isoquinolines, thiocyanation of phenylimidazopyridines, functionalization of quinolinones by allowing regioselective installation of an SCN, SeCN, SPh, SePh, Cl, Br, or I group at the C-3 position, and isomerization of alkenes. Mechanistic investigations suggest an oxidative photoredox process for oxygenation and C-H functionalization, while isomerization is believed to proceed through a photosensitization pathway.

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 Isomerisation Catalysed by a Superbasic Sodium Amide.

Typically 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.

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.

Iron in Organometallic Transformations: A Sustainable Substitute for Noble Metals

AbstractTransition metal catalysis plays a pivotal role in chemical synthesis. Noble metals often grab significant attention in organometallic catalysis due to their high reactivity. However, the serious issues associated with these metals such as low abundance, toxicity, geopolitical limitations, and volatile prices are driving the scientific community to discover sustainable alternatives. In this context, iron appears to be the first choice as an alternative metal due to its unique properties, including a range of stable oxidation states, Lewis acidity, high abundance in the earth‘s crust, and low toxicity. Over the past two decades, substantial progress has been made in iron catalysis. This overview examines the recent developments in iron‐catalyzed industrially relevant transformations such as hydroformylation, olefin isomerization, hydrosilylation, hydrophosphination, carbonylation, Wacker‐type oxidation, and plastic depolymerization. As witnessed throughout this review, the performance of iron can be significantly altered by suitable ligand selection and by tailoring the electronic and steric properties of the iron center. While noble metals remain the industry work‐horse, iron is inching closer and with extensive scientific understanding, it may replace noble metals in the near future.

Remote Functionalization by Pd-Catalyzed Isomerization of Alkynyl Alcohols.

In recent years, progress has been made in the development of catalytic methods that allow remote functionalizations based on alkene isomerization. In contrast, protocols based on alkyne isomerization are comparatively rare. Herein, we report a general Pd-catalyzed long-range isomerization of alkynyl alcohols. Starting from aryl-, heteroaryl-, or alkyl-substituted precursors, the optimized system provides access preferentially to the thermodynamically more stable α,β-unsaturated aldehydes and is compatible with potentially sensitive functional groups. We showed that the migration of both π-components of the carbon-carbon triple bond can be sustained over several methylene units. Computational investigations served to shed light on the key elementary steps responsible for the reactivity and selectivity. These include an unorthodox phosphine-assisted deprotonation rather than a more conventional β-hydride elimination in the final tautomerization event.