Olefinic Substrates Research Articles

Electrochemically enabled (3+2) cycloaddition of unbiased alkenes and β-dicarbonyls.

A (3+2) cycloaddition between unbiased alkenes and 1,3-dicarbonyls is accomplished by judicious choice of electrode material and electrocatalyst to access dihydrofuran derivatives. A fluorinated porous carbon electrode with appropriate thickness governs unprecedented reactivity. This methodology eliminates the necessity for any stabilizing group within the alkene substrate. This is a rare example of the annulation of unbiased internal and terminal alkenes with cyclic and acyclic β-dicarbonyls.

NiH-catalyzed C-N bond formation: insights and advancements in hydroamination of unsaturated hydrocarbons.

The formation of C-N bonds is a fundamental aspect of organic synthesis, and hydroamination has emerged as a pivotal strategy for the synthesis of essential amine derivatives. In recent years, there has been a surge of interest in metal hydride-catalyzed hydroamination reactions of common alkenes and alkynes. This method avoids the need for stoichiometric organometallic reagents and overcomes problems associated with specific organometallic compounds that may impact functional group compatibility. Notably, recent developments have brought to the forefront olefinic hydroamination and hydroamidation reactions facilitated by nickel hydride (NiH) catalysis. The inclusion of suitable chiral ligands has paved the way for the realization of asymmetric hydroamination reactions in the realm of olefins. This review aims to provide an in-depth exploration of the latest achievements in C-N bond formation through intermolecular hydroamination catalyzed by nickel hydrides. Leveraging this innovative approach, a diverse range of alkene and alkyne substrates can be efficiently transformed into value-added compounds enriched with C-N bonds. The intricacies of C-N bond formation are succinctly elucidated, offering a concise overview of the underlying reaction mechanisms. It is our aspiration that this comprehensive review will stimulate further progress in NiH-catalytic techniques, fine-tune reaction systems, drive innovation in catalyst design, and foster a deeper understanding of the underlying mechanisms.

Direct access to furan and cyclopropane derivatives via palladium-catalyzed C-H activation/alkene insertion/annulation.

A practical and effective palladium-catalyzed C-H activation/alkene insertion/annulation has been reported for the synthesis of furans and cyclopropanes from cyclic 1,3-diketones or 1,3-indandione and diverse alkenes, resulting in moderate to good yields. This protocol demonstrates excellent selectivity and is well-compatible with a wide range of alkene substrates, exhibiting exceptional regioselectivities, high efficiency, and good functional group tolerance.

Hydroboration and hydrosilylation of alkenes catalyzed by an unsymmetrical magnesium methyl complex.

The hydroboration and hydrosilylation of alkenes catalyzed by the unsymmetrical β-diketiminate magnesium methyl complex [(DippXylNacnac)MgMe (THF)] (1) have been reported. When complex 1 was employed as a highly efficient catalyst in the hydroboration of various alkenes with HBpin, only the anti-Markovnikov hydroboration products were obtained in high yields and with high regioselectivities under mild reaction conditions (60 °C). To our surprise, it showed different regioselectivities in the hydrosilylation of a range of alkenes with PhSiH3. Aromatic alkene substrates afforded the corresponding branched Markovnikov hydrosilylation products in high yields and with high regioselectivities; conversely, aliphatic alkenes produced the linear anti-Markovnikov products in moderate yields. This is completely consistent with the corresponding density functional theory (DFT) calculations. In addition, the practical utility was demonstrated via scale-up reactions of boronate esters and a preliminary plausible mechanism of hydroboration and hydrosilylation have been investigated as well.

Substrate scope driven optimization of an encapsulated hydroformylation catalyst.

Caged complexes can provide impressive selective catalysts. Due to the complex shapes of such caged catalysts, however, the level of selectivity control of a single substrate cannot be extrapolated to other substrates. Herein, the substrate scope using 41 terminal alkene substrates is investigated in the hydroformylation reaction with an encapsulated rhodium catalyst [Rh(H)(CO)3(P(mPy3(ZnTPP)3))] (CAT1). For all substrates, the amount of branched products formed was higher with CAT1 than with the unencapsulated reference catalyst [Rh(H)(CO)2(P(mPy3))2] (CAT2) (linear/branched ratio between 2.14 and 0.12 for CAT1 and linear/branched ratio between 6.22 and 0.59 for CAT2). Interestingly, the level of cage induced selectivity depends strongly on the substrate structure that is converted. Analysis of the substrate scope combined with DFT calculations suggests that noncovalent interactions between the substrate moieties and cage walls play a key role in controlling the regioselectivity. Consequently, these supramolecular interactions were further optimized by replacing the ZnTPP building block with a zinc porphyrin analog that contained OiPr substituents on the meta position of the aryl rings. The resulting caged catalyst, CAT4, converted substrates with even higher branched selectivity.

Electrochemical N-olefination for the regio- and stereo-selective synthesis of vinyl azoles

A selenium-catalyzed electrosynthesis involving regio- and stereo-selective N-olefination of azoles was developed. The room-temperature reaction was efficient (up to 97 ​% yield) and compatible with various styrenes and azoles. Mechanistic study showed that the cascade reaction was triggered by the selenium-cation-mediated electrophilic trans-aminoselenation, and followed by an oxidative cis-elimination of selane. The electrosynthesis was also well compatible with the more challenging internal alkene substrates, giving the desired N-vinyl azoles in up to 88 ​% yield and >20:1 Z/E ratio.

The Synthesis of (E)‐Vinyl and Alkynyl Sulfones by the Formation of an Electron Donor‐Acceptor Complex Using Thiosulfonates and Sodium Iodide Under Visible Light

AbstractA method for the synthesis of (E)‐vinyl sulfones and alkynyl sulfones through the cleavage of thiosulfonate promoted by the formation of EDA complexes under visible light irradiation at room temperature without the need for other metal catalysts is described. The mechanism study shows that sodium iodide and thiosulfonate form EDA complexes under visible light irradiation, resulting in a single‐electron transfer cleavage to generate sulfonyl radicals, which then react with olefins or alkynes to produce (E)‐vinyl sulfones or alkynyl sulfones, respectively. This method is applicable to 44 olefin and alkyne substrates, with yields ranging from 38% to 90%, providing a radical synthesis approach for the preparation of sulfonylated compounds.

Asymmetric Photoaerobic Lactonization and Aza-Wacker Cyclization of Alkenes Enabled by Ternary Selenium-Sulfur Multicatalysis.

An adaptable, sulfur-accelerated photoaerobic selenium-π-acid ternary catalyst system for the enantioselective allylic redox functionalization of simple, nondirecting alkenes is reported. In contrast to related photoredox catalytic methods, which largely depend on olefinic substrates with heteroatomic directing groups to unfold high degrees of stereoinduction, the current protocol relies on chiral, spirocyclic selenium-π-acids that covalently bind to the alkene moiety. The performance of this ternary catalytic method is demonstrated in the asymmetric, photoaerobic lactonization and cycloamination of enoic acids and unsaturated sulfonamides, respectively, leading to an averaged enantiomeric ratio (er) of 92:8. Notably, this protocol provides for the first time an asymmetric, catalytic entryway to pharmaceutically relevant 3-pyrroline motifs, which was used as a platform to access a 3,4-dihydroxyproline derivative in only seven steps with a 92:8 er.

Ring‐Opening Coupling Reaction of Cyclopropanols with Electrophilic Alkenes Enabled by Decatungstate as Photoredox Catalyst

AbstractWe introduce a methodology for the photocatalytic generation of β‐ketoalkyl radicals from tertiary cyclopropanols, utilizing tetrabutylammonium decatungstate (TBADT) as a photoredox catalyst. The application is demonstrated by the synthesis of distantly functionalized ketones via the redox‐neutral addition of the cyclopropanol‐derived β‐ketoalkyl radicals to the double bond of electrophilic olefins. The transformation occurs under ambient temperature conditions and is suitable for coupling a wide range of cyclopropanol and alkene substrates. This was demonstrated by the preparation of 33 ketone products with 35–92% yield. The method's preparative robustness has been validated through upscaled preparations conducted under continuous flow conditions. Mechanistic investigations support the role of TBADT as a photoredox catalyst, which facilitates the single electron oxidation of cyclopropanols, followed by the electron transfer from the reduced form of decatungstate to the electrophilic double bond of alkene. Moreover, we found that electron‐rich aromatic cyclopropanols and electron‐deficient olefins form photoactive electron donor‐acceptor (EDA) complexes. This property allows the reaction to proceed under UV light irradiation via the photoinduced charge transfer in the absence of the photocatalyst.

Nickel-catalyzed direct stereoselective α-allylation of ketones with non-conjugated dienes

The development of efficient and sustainable methods for the construction of carbon-carbon bonds with the simultaneous stereoselective generation of vicinal stereogenic centers is a longstanding goal in organic chemistry. Low-valent nickel(0) complexes which promote α-functionalization of carbonyls leveraging its pro-nucleophilic character in conjunction with suitable olefin acceptors are scarce. We report a Ni(0)NHC catalyst which selectively converts ketones and non-conjugated dienes to synthetically highly valuable α-allylated products. The catalyst directly activates the α-hydrogen atom of the carbonyl substrate transferring it to the olefin acceptor. The transformation creates adjacent quaternary and tertiary stereogenic centers in a highly diastereoselective and enantioselective manner. Computational studies indicate the ability of the Ni(0)NHC catalyst to trigger a ligand-to-ligand hydrogen transfer process from the ketone α-hydrogen atom to the olefin substrate, setting the selectivity of the process. The shown selective functionalization of the α-C-H bond of carbonyl groups by the Ni(0)NHC catalyst opens up new opportunities to exploit sustainable 3d-metal catalysis for a stereoselective access to valuable chiral building blocks.

Surface Chain-Transfer Ring-Opening Metathesis Polymerization.

Ring-opening metathesis polymerization (ROMP) is a powerful method to graft various types of polymer chains to a given surface. While surface-initiated ROMP (SI-ROMP) serves as an efficient tool for surface modification and is therefore widely reported, the method requires grafting (1) the olefin substrate and (2) the metathesis catalyst to the surface prior to the polymerization with multiple synthetic and work up steps. To overcome this difficulty, we proposed the use of the chain-transfer reaction as an alternative method for surface modification. Terminal olefins are grafted to the surface without the need to graft the metathesis catalysts, and polymers with olefin backbones are polymerized and grafted simultaneously via both ROMP and chain transfer (cross-metathesis between olefins from backbones and surfaces). Compared to SI-ROMP, this surface-chain transfer ROMP (SC-ROMP) method avoids grafting the catalyst and growing polymer chains from the surface and could be achieved in a single step. Various types of surfaces like carbon nanotubes, carbon fibers, graphene nanosheets, and silica microspheres are used for demonstration. We envision that this work could bring a convenient and effective solution to surface modification via ROMP.

Room temperature electro-carboxylation of styrene and stilbene derivatives: A comparative study

The use of carbon dioxide as a comparatively cheap, abundant and non-toxic C-1 synthon is a topic of considerable interest and importance. The electrochemical addition of carbon dioxide across carbon–carbon double bonds is one of the more promising of such procedures, offering the possibility to convert a range of alkene substrates to valuable carboxylated products. However, much remains unknown about both the mechanism of reaction and how to influence product specificity during electro-carboxylation of alkenes. Herein, we explore the electrochemical addition of carbon dioxide (1 atm) to a range of olefinic substrates using nickel working electrodes and magnesium anodes at room temperature, producing the mono-substituted carboxylate derivatives preferentially (with no formation of the Markovnikov isomers of these mono-substituted carboxylate derivatives when the starting materials are non-symmetrical). These findings are rationalized using both experimental and computational methods, suggesting that the choice of Ni as a working electrode is critical in determining the reaction outcomes that are observed. Moreover, we also present direct evidence that a pathway whereby the alkene substrates are first reduced at the electrode surface and then react with dissolved CO2 is operating. Together, these results offer the potential for selective access to a range of valuable mono-carboxylic acids via the reduction of the corresponding alkene precursors in the presence of carbon dioxide.

Efficient Method for the Preparation of Ozonides Under Dry Conditions

Abstract An efficient method for the preparation of ozonides via the reaction of alkenes and ozone under dry conditions is described. The influx of a pre-dried ozone stream into a dichloromethane solution of the olefinic substrates in the presence of molecular sieve 4Å afforded the corresponding ozonides in good to high yields. The reaction in the absence of a molecular sieve gave poor results. The structure of the ozonide was unambiguously confirmed by XRD analysis.

Regioselective, catalytic 1,1-difluorination of enynes.

Fluorinated small molecules are prevalent across the functional small-molecule spectrum, but the scarcity of naturally occurring sources creates an opportunity for creative endeavour in developing routes to access these important materials. Iodine(I)/iodine(III) catalysis has proven to be particularly well-suited to this task, enabling abundant alkene substrates to be readily intercepted by in situ-generated λ3-iodanes and processed to high-value (di)fluorinated products. These organocatalysis paradigms often emulate metal-based processes by engaging the π bond and, in the case of styrenes, facilitating fluorinative phenonium-ion rearrangements to generate difluoromethylene units. Here we demonstrate that enynes are competent proxies for styrenes, thereby mitigating the recurrent need for aryl substituents, and enabling highly versatile homopropargylic difluorides to be generated in an operationally simple manner. The scope of the method is disclosed, together with application in target synthesis (>30 examples, up to >90% yield).

Nitrate radicals generated by TiO2 heterogeneous photocatalysis: Application to the cleavage of C=C double bond to carbonyl compounds

The oxidative cleavage of alkenes represents a relevant chemical process with immense potential for the synthesis of partially oxidized compounds. Several methodologies have been proposed for achieving oxidative cleavage of alkenes, aiming to obtain carbonyl products. However, none of these approaches have been successfully scaled up for industrial applications beyond the laboratory scale. In this study, we report the selective photocatalytic oxidative cleavage of limonene to limononaldehyde using irradiated TiO2 suspensions in the presence of silver nitrate under ambient conditions. Results demonstrate that within one hour of irradiation, a notable conversion and selectivity of 60% towards limononaldehyde can be achieved. The investigation reveals that the oxidation process is primarily driven by nitrate radicals, generated through hole-induced oxidation of nitrate ions. Notably, this selective photocatalytic approach shows potentials that bode well for its application to other olefinic substrates in addition to limonene. These results present a promising pathway for the scalable industrial synthesis of partially oxidized compounds through selective photocatalytic oxidation of alkenes.

HPW/MCM-41 catalytic Simmons-Smith cyclopropanation of olefins for synthesis of high-energy–density fuel

Simmons-Smith cyclopropanation commonly promoted by CF3COOH is one important method for transforming olefin into high-energy–density cyclopropyl fuel, but it brings problems such as high cost and harm to environment. In this work, a series of highly active solid acid catalysts HPW/MCM-41 is prepared by impregnation method for the cyclopropanation of dicyclopentadiene. The composition, structural and acidity of catalyst were characterized by TEM, XRD, NH3-TPD, etc. The 5 % HPW/MCM-41 contains more Dawson-type P2W18 (H6P2W18O62) and defective-type P2W21 (H6P2W21O71) that can provide the most abundant acid sites. This catalyst shows the best catalytic activity, the conversion and bicyclic product selectivity for cyclopropanation of dicyclopentadiene are 93.4 % and 55.7 %, respectively, both higher than that of CF3COOH. Moreover, such catalyst shows good catalytic activity for several olefin substrates, and can be recycled in several runs. This work provides a green and efficient catalyst for cyclopropanation reactions for synthesis of high-energy–density fuel, pesticide and medicine.

Effect of Solvent on the Rate of Ozonolysis: Development of a Homogeneous Flow Ozonolysis Protocol.

Herein, we describe the effect of organic solvents on ozone solubility and the rate of ozonolysis reactions using rapid injection NMR spectroscopy. The tabulated solubility and kinetic data allowed for the design of a homogeneous ozonolysis flow reactor capable of delivering precise quantities of dissolved ozone to various olefin substrates.

Pd-Catalyzed Tandem Pathway for Stereoselective Synthesis of (E)-1,3-Enyne from β-Nitroalkenes by Using a Sacrificial Directing Group.

The involvement of nitroalkenes instead of minimal one alkyne motif for (E)-1,3-enynes synthesis through a palladium catalyzed stereoselective bond forming pathway at room temperature is presented. Implication of nitro group as a sacrificial directing group, formation of magical alkyne on a newly developed Csp 3 -Csp 3 bond with initial palladium-MBH adduct make this methodology distinctive. This protocol features an unprecedented sequential acetate addition, carbon-carbon bond formation, isomerization of double bond and nitromethane degradation in a tandem catalytic walk via dancing hybridization. Mechanistic understanding through identification of intermediates and computational calculations furnishes complete insight into the tandem catalytic pathway. Broad substrates scope and functional groups tolerance make this synthetic methodology magnificent and dynamic. This represents the first example of stereoselective 1,3-enyne synthesis exclusively from alkene substrates by introducing the concept of sacrificial directing group.

Synthetically Useful Transformations of Olefins via Cationic 1,2-Oxazetium Intermediates.

Nitrosyl triflate serves as a NO+ donor in reactions with many olefinic substrates to form reactive, cationic 1,2-oxazetium cycloadducts that can be converted selectively into a wide range of useful products depending on reagents and conditions.

Rh nanoparticles anchored on phosphorous-doped porous carbon for efficiently catalytic hydroformylation of alkenes

The hydroformylation of alkenes to prepare aldehydes using rhodium-based catalysts has been widely investigated, while homogeneous Rh catalysts always suffer from poor reusability. Herein, a promising solution was proposed to introduce phosphorous heteroatoms into a porous carbon support to fabricate a stable and efficient catalyst (Rh/P-mC). And the obtained Rh/P-mC had high hydroformylation activity under mild reaction conditions. The substrate expansion experiment using different alkene substrates and the catalyst cycling experiment demonstrated the universality and stability of this catalyst. The hydroformylation reaction mechanism was also proposed, and the effect of the interaction between phosphorus and rhodium on the hydroformylation reaction was verified. Thus, this work has great application prospects for the highly efficient catalytic hydroformylation of alkenes and provides an efficient method for the design of high-performance hydroformylation catalysts.