Non-conjugated Olefins Research Articles

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.

Extraction and Characterization of Cellulosic Fiber from Banana, Sugarcane, and Napier Grass

Cellulosic fibers are one of the trend studies being conducted from the recent research due to their cost-effectiveness and abundance as biomass waste products from different plantations. The study aims to fabricate a dew extractor machine and analyze and characterize fibers based on their physical, mechanical, and chemical properties. The machine achieved the required torque, which is 370.645 N.m, and a speed of 28.82 rpm for the initial process for the sources of fiber by using a chain drive. Among the three fibers, the banana shows greater tensile strength with 221.225 MPa - 418.59 7MPa for untreated and 191.376 MPa – 715.428 MPa for treated. Napier has the smallest value of tensile strength with 77.944 MPa – 146.731 MPa for untreated and 76.048 MPa – 287.689 MPa for treated. The chemical properties of the fibers were analyzed using Fourier Transform Infrared Spectroscopy shows all three fibers have a similar single-, triple- and double-bond, namely a secondary aliphatic alcohol, alkene, and a non-conjugated alkene functional group. It can be concluded that treated fibers can withstand more stress, stretch even more, and therefore are more elastic than untreated fibers.

Machine learning models for binary molecular classification using VUV absorption spectra

Machine learning methods were combined with differential absorption spectroscopy measurements in the vacuum-ultraviolet region (5.167 – 9.920 eV) in order to develop predictive capabilities for inferring molecular structure from the spectra. Several types of species were analyzed and, for modeling purposes, were defined using a single classification: (1) alkane, (2) conjugation with oxygen (e.g. diacetyl, ethyl vinyl ether), (3) non-conjugated alkene (e.g. 1-butene, 1,4-cyclohexadiene), (4) oxygen-containing (e.g. 1-butanol, tetrahydrofuran), or (5) cyclic (e.g. cyclopentane, cyclohexanone). The latter molecular classification excluded cyclic ethers. Several modeling methods were employed in the analysis of 102 absorption spectra, 24 of which were measured for the first time.The primary objective was to identify suitable methods that enable accurate predictions of molecular structure classifications with minimized statistical uncertainties. Rather than identifying a single, unifying method to reliably predict molecular structure contributions to VUV absorption spectra, coordination is required among a particular method, the type of molecular structure detail (e.g. conjugation), and absorption region of interest. The latter is accomplished using a binning approach, wherein absorption regions of ∼0.5 eV were utilized rather than the entire ∼4.8 eV range. Photon energy binning enabled analysis of region-specific predictions of accuracy, precision, and recall. The outcome from the binning approach is that, rather than utilizing the entire spectrum, optimal determination of molecular structure using machine learning methods depends on the absorption region. The present work provides separate machine learning models for each molecular classification, which enables the identification of multi-functional species relevant to atmospheric chemistry and combustion chemistry, where isomer-resolved speciation is critical to understanding complex reaction networks.

Mapping Ambiphile Reactivity Trends in the Anti-(Hetero)annulation of Non-Conjugated Alkenes via PdII /PdIV Catalysis.

In this study, we systematically evaluate different ambiphilic organohalides for their ability to participate in anti-selective carbo- or heteroannulation with non-conjugated alkenyl amides under PdII /PdIV catalysis. Detailed optimization of the reaction conditions has led to protocols for synthesizing tetrahydropyridines, tetralins, pyrrolidines, and other carbo/heterocyclic cores via [n+2] (n=3-5) (hetero)annulation. Expansion of scope to otherwise unreactive ambiphilic haloketones through PdII /amine co-catalysis is also demonstrated. Compared to other annulation processes, this method proceeds via a distinct PdII /PdIV mechanism involving Wacker-type directed nucleopalladation. This difference results in unique reactivity and selectivity patterns, as revealed through assessment of reaction scope and competition experiments.

Mechanistic Studies of Pd(II)-Catalyzed E/Z Isomerization of Unactivated Alkenes: Evidence for a Monometallic Nucleopalladation Pathway.

Pd(II)-catalyzed E/Z isomerization of alkenes is a common process-yet its mechanism remains largely uncharacterized, particularly with non-conjugated alkenes. In this work, the mechanism of Pd(II)-catalyzed E/Z isomerization of unactivated olefins containing an aminoquinoline-based amide directing group is probed using in situ kinetic analysis, spectroscopic studies, kinetic modeling, and DFT calculations. The directing group allows for stabilization and monitoring of previously undetectable intermediates. Collectively, the data are consistent with isomerization occurring through a monometallic nucleopalladation mechanism.

Olefin Epoxidation Catalyzed by Titanium–Salalen Complexes: Synergistic H2O2 Activation by Dinuclear Ti Sites, Ligand H-Bonding, and π-Acidity

Titanium–salalen complexes have recently solved a long-standing problem in homogeneous epoxidation catalysis by enabling the selective catalytic epoxidation of terminal, nonconjugated olefins with ...

Directed Markovnikov hydroarylation and hydroalkenylation of alkenes under nickel catalysis.

We report a full account of our research on nickel-catalyzed Markovnikov-selective hydroarylation and hydroalkenylation of non-conjugated alkenes, which has yielded a toolkit of methods that proceed under mild conditions with alkenyl sulfonamide, ketone, and amide substrates. Regioselectivity is controlled through catalyst coordination to the native Lewis basic functional groups contained within these substrates. To maximize product yield, reaction conditions were fine-tuned for each substrate class, reflecting the different coordination properties of the directing functionality. Detailed kinetic and computational studies shed light on the mechanism of this family of transformations, pointing to transmetalation as the turnover-limiting step.

Anti-selective [3+2] (Hetero)annulation of non-conjugated alkenes via directed nucleopalladation

2,3-Dihydrobenzofurans and indolines are common substructures in medicines and natural products. Herein, we describe a method that enables direct access to these core structures from non-conjugated alkenyl amides and ortho-iodoanilines/phenols. Under palladium(II) catalysis this [3 + 2] heteroannulation proceeds in an anti-selective fashion and tolerates a wide variety of functional groups. N-Acetyl, -tosyl, and -alkyl substituted ortho-iodoanilines, as well as free –NH2 variants, are all effective. Preliminary results with carbon-based coupling partners also demonstrate the viability of forming indane core structures using this approach. Experimental and computational studies on reactions with phenols support a mechanism involving turnover-limiting, endergonic directed oxypalladation, followed by intramolecular oxidative addition and reductive elimination.

Integrating Allyl Electrophiles into Nickel-Catalyzed Conjunctive Cross-Coupling.

Allylation and conjunctive cross-coupling represent two useful, yet largely distinct, reactivity paradigms in catalysis. The union of these two processes would offer exciting possibilities in organic synthesis but remains largely unknown. Herein, we report the use of allyl electrophiles in nickel-catalyzed conjunctive cross-coupling with a non-conjugated alkene and dimethylzinc. The transformation is enabled by weakly coordinating, monodentate aza-heterocycle directing groups that are useful building blocks in synthesis, including saccharin, pyridones, pyrazoles, and triazoles. The reaction occurs under mild conditions and is compatible with a wide range of allyl electrophiles. High chemoselectivity through substrate directivity is demonstrated by the facile reactivity of the β-γ alkene of the starting material, whereas the ϵ-ζ alkene of the product is preserved. The generality of this approach is further illustrated through the development of an analogous method with alkyne substrates. Mechanistic studies reveal the importance of the dissociation of the weakly coordinating directing group to allow the allyl moiety to bind and facilitate C(sp3 )-C(sp3 ) reductive elimination.

Trifluoromethylations of Alkenes Using PhICF3Cl as Bifunctional Reagent.

We described a trifluoromethylation of alkenes using PhICF3Cl as bifunctional reagent. Chlorotrifluoromethylated products were obtained when nonconjugated alkenes were treated with PhICF3Cl in 1,4-dioxane at 60 °C, while vinyl C-H trifluoromethylated products were obtained by further elimination of hydrochloride in the case of those conjugated alkene substrates in DMF. Broad substrate scope, especially including complex alkenes bearing biological active motifs, suggests that this mild reaction is feasible for late-stage modification in drug discovery.

Lithium–Olefin π-Complexes and the Mechanism of Carbolithiation: Synthesis, Solution Behavior, and Crystal Structure of (2,2-Dimethylpent-4-en-1-yl)lithium

We describe the first crystallographically characterized example of a nonconjugated olefin bound in a simple dihapto fashion to a lithium center, as part of a study of two alkyllithium compounds that contain C═C double bonds at the alkyl chain terminus: (2,2-dimethylbut-3-en-1-yl)lithium (1) and the related pentenyl compound (2,2-dimethylpent-4-en-1-yl)lithium (2). The Li–olefin interactions in the crystal structure of 2 serve as a model for those proposed to be present in the [RLi···olefin] intermediate in olefin carbolithiation reactions. As seen in other systems, the Li–olefin interaction is correlated with deshielding of the 1H NMR resonances of the olefinic hydrogen atoms. DOSY and NOE measurements show that 1 and 2 remain tetrameric in cyclohexane and that the lithium–olefin interactions persist in solution. Addition of a Lewis base such as THF to these ω-alkenyllithium species has two effects: the THF displaces the lithium–olefin interactions while accelerating the rate of carbolithiation. A deuteration experiment shows that compound 2 undergoes reversible carbolithiation to the corresponding cyclobutylmethyllithium species in the presence of Lewis bases, but this transformation is thermodynamically uphill owing to ring strain. In comparison, the longer chain hexenyl species (2,2-dimethylhex-5-en-1-yl)lithium is thermodynamically unstable with respect to the intramolecular carbolithiation product [(3,3-dimethylcyclopentyl)methyl]lithium (3). We suggest that rate-determining step in carbolithiation reactions may not always be formation of the C–C bond, as is often assumed, but in some cases may be formation of the lithium–olefin complex; the coordination of the olefin to lithium may occur in a concerted fashion with disaggregation of lithium clusters. Finally, we point out that activation enthalpies can be obtained solely from NMR line shapes above the coalescence point.

Catalytic, Enantioselective α-Alkylation of Azlactones with Nonconjugated Alkenes by Directed Nucleopalladation.

A palladium(II)-catalyzed enantioselective α-alkylation of azlactones with nonconjugated alkenes is described. The reaction employs a chiral BINOL-derived phosphoric acid as the source of stereoinduction, and a cleavable bidentate directing group appended to the alkene to control the regioselectivity and stabilize the nucleopalladated alkylpalladium(II) intermediate in the catalytic cycle. A wide range of azlactones were found to be compatible under the optimal reaction conditions to afford products bearing α,α-disubstituted α-amino-acid derivatives with high yields and high enantioselectivity.

Catalytic, Enantioselective α‐Alkylation of Azlactones with Nonconjugated Alkenes by Directed Nucleopalladation

AbstractA palladium(II)‐catalyzed enantioselective α‐alkylation of azlactones with nonconjugated alkenes is described. The reaction employs a chiral BINOL‐derived phosphoric acid as the source of stereoinduction, and a cleavable bidentate directing group appended to the alkene to control the regioselectivity and stabilize the nucleopalladated alkylpalladium(II) intermediate in the catalytic cycle. A wide range of azlactones were found to be compatible under the optimal reaction conditions to afford products bearing α,α‐disubstituted α‐amino‐acid derivatives with high yields and high enantioselectivity.

Noble-Metal Substitution in Hemoproteins: An Emerging Strategy for Abiological Catalysis.

Enzymes have evolved to catalyze a range of biochemical transformations with high efficiencies and unparalleled selectivities, including stereoselectivities, regioselectivities, chemoselectivities, and substrate selectivities, while typically operating under mild aqueous conditions. These properties have motivated extensive research to identify or create enzymes with reactivity that complements or even surpasses the reactivity of small-molecule catalysts for chemical reactions. One of the limitations preventing the wider use of enzymes in chemical synthesis, however, is the narrow range of bond constructions catalyzed by native enzymes. One strategy to overcome this limitation is to create artificial metalloenzymes (ArMs) that combine the molecular recognition of nature with the reactivity discovered by chemists. This Account describes a new approach for generating ArMs by the formal replacement of the natural iron found in the porphyrin IX (PIX) of hemoproteins with noble metals. Analytical techniques coupled with studies of chemical reactivity have demonstrated that expression of apomyoglobins and apocytochrome P450s (for which "apo-" denotes the cofactor-free protein) followed by reconstitution with metal-PIX cofactors in vitro creates proteins with little perturbation of the native structure, suggesting that the cofactors likely reside within the native active site. By means of this metal substitution strategy, a large number of ArMs have been constructed that contain varying metalloporphyrins and mutations of the protein. The studies discussed in this Account encompass the use of ArMs containing noble metals to catalyze a range of abiological transformations with high chemoselectivity, enantioselectivity, diastereoselectivity, and regioselectivity. These transformations include intramolecular and intermolecular insertion of carbenes into C-H, N-H, and S-H bonds, cyclopropanation of vinylarenes and of internal and nonconjugated alkenes, and intramolecular insertions of nitrenes into C-H bonds. The rates of intramolecular insertions into C-H bonds catalyzed by thermophilic P450 enzymes reconstituted with an Ir(Me)-PIX cofactor are now comparable to the rates of reactions catalyzed by native enzymes and, to date, 1000 times greater than those of any previously reported ArM. This reactivity also encompasses the selective intermolecular insertion of the carbene from ethyl diazoacetate into C-H bonds over dimerization of the carbene to form alkenes, a class of carbene insertion or selectivity not reported to occur with small-molecule catalysts. These combined results highlight the potential of well-designed ArMs to catalyze abiological transformations that have been challenging to achieve with any type of catalyst. The metal substitution strategy described herein should complement the reactivity of native enzymes and expand the scope of enzyme-catalyzed reactions.

Three-component vicinal-diarylation of alkenes via direct transmetalation of arylboronic acids.

Herein, we report three-component vicinal-diarylation of non-conjugated alkenes initiated by transmetalation of arylboronic acids, which provides complementary access to β,γ-diaryl carbonyl compounds. We have also screened a large number of chiral ligands for developing an enantioselective version of this reaction and obtained the preliminary results (up to 79 : 21 e.r.). Notably, the methodology developed herein represents the first three component syn-vicinal-dicarbofunctionalization of non-conjugated alkenes involving palladium catalysis.

Visible-Light-Driven Epoxyacylation and Hydroacylation of Olefins Using Methylene Blue/Persulfate System in Water.

A visible-light-driven strategy for hydroacylation and epoxyacylation of olefins in water using methylene blue as photoredox catalyst and persulfate as oxidant is reported. In this unprecedented unified approach, two different transformations are accomplished using only one set of reagents. The method has a broad scope spanning a range of aromatic and aliphatic aldehydes as well as conjugated and nonconjugated olefins to deliver ketones and epoxyketones from abundant and inexpensive chemical feedstocks.

Direct Access to Versatile Electrophiles via Catalytic Oxidative Cyanation of Alkenes.

Nucleophilic attack on carbon-based electrophiles is a central reactivity paradigm in chemistry and biology. The steric and electronic properties of the electrophile dictate its reactivity with different nucleophiles of interest, allowing the opportunity to fine-tune electrophiles for use as coupling partners in multistep organic synthesis or for covalent modification of proteins in drug discovery. Reactions that directly transform inexpensive chemical feedstocks into versatile carbon electrophiles would therefore be highly enabling. Herein, we report the catalytic, regioselective oxidative cyanation of conjugated and nonconjugated alkenes using a homogeneous copper catalyst and a bystanding N-F oxidant to furnish branched alkenyl nitriles that are difficult to prepare using existing methods. We show that the alkenyl nitrile products serve as electrophilic reaction partners for both organic synthesis and the chemical proteomic discovery of covalent protein ligands.

C(alkenyl)-H Activation via Six-Membered Palladacycles: Catalytic 1,3-Diene Synthesis.

A catalytic method to prepare highly substituted 1,3-dienes from two different alkenes is described using a directed, palladium(II)-mediated C(alkenyl)-H activation strategy. The transformation exhibits broad scope across three synthetically useful substrate classes masked with suitable bidentate auxiliaries (4-pentenoic acids, allylic alcohols, and bishomoallylic amines) and tolerates internal nonconjugated alkenes, which have traditionally been a challenging class of substrates in this type of chemistry. Catalytic turnover is enabled by either MnO2 as the stoichiometric oxidant or co-catalytic Co(OAc)2 and O2 (1 atm). Experimental and computational studies were performed to elucidate the preference for C(alkenyl)-H activation over other potential pathways. As part of this effort, a structurally unique alkenylpalladium(II) dimer was isolated and characterized.

Directed nickel-catalyzed 1,2-dialkylation of alkenyl carbonyl compounds.

A nickel-catalyzed conjunctive cross-coupling of non-conjugated alkenes, alkyl halides, and alkylzinc reagents is reported. Regioselectivity is controlled by chelation of a removable bidentate 8-aminoquinoline directing group. Under optimized conditions, a wide range of 1,2-dialkylated products can be accessed in moderate to excellent yields. To the best of our knowledge, this report represents the first example of three-component 1,2-dialkylation of non-conjugated alkenes to introduce differentiated alkyl fragments.

Regioselective Hydroamination Using a Directed Nucleopalladation/Protodepalladation Strategy

Alkene hydroamination is an attractive approach for converting alkenes into structurally complex amine products. Several different strategies have been pursued over the past few decades to achieve this historically challenging reaction. One of the key issues associated with this transformation is control of regioselectivity, which is particularly difficult for internal non-conjugated alkenes. Our group has recently found success using a removable bidentate auxiliary to control regioselectivity and stabilize the key nucleopalladated intermediate in a palladium(II)-catalyzed alkene hydroamination with N–H nucleophiles. This article describes the historical context for this work, the underlying conceptual logic, our results to date, and the future outlook.