Acyclic Olefins 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.

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.

Diastereoselective Hydrodifluoromethylation of Alkenyl N-Heterocycles via Photocatalytic Radical-Polar Crossover.

A diastereoselective hydrodifluoromethylation of N-heteroaryl alkenes was successfully established. This method was applicable to an array of N-heteroaryl substrates with both cyclic and acyclic alkenes while displaying tolerance to a variety of functional groups. The conditions were also expanded to obtain hydrotrifluoromethylated products with similar results. Initial mechanistic studies suggest that the final protonation step is accessed through a radical-polar crossover process.

Photoinduced Copper-Catalyzed Enantioselective Allylic C(sp3)-H Oxidation of Acyclic 1-Aryl-2-alkyl Alkenes as Limiting Substrates.

Herein, we disclose a simple copper-catalyzed method for enantioselective allylic C(sp3)-H oxidation of unsymmetrical acyclic alkenes, specifically 1-aryl-2-alkyl alkenes. The C-H substrates are used in limiting amounts, and the products are obtained with high enantioselectivity, E/Z-selectivity, and regioselectivity. The method exhibits broad functional group tolerance, and E/Z-alkene mixtures are suitable C-H substrates. The transformation is enabled by light irradiation, which sustains the enantioselective copper catalysis by photoinduced oxidant homolysis.

Photoinduced Copper‐Catalyzed Enantioselective Allylic C(sp3)−H Oxidation of Acyclic 1‐Aryl‐2‐alkyl Alkenes as Limiting Substrates

AbstractHerein, we disclose a simple copper‐catalyzed method for enantioselective allylic C(sp3)−H oxidation of unsymmetrical acyclic alkenes, specifically 1‐aryl‐2‐alkyl alkenes. The C−H substrates are used in limiting amounts, and the products are obtained with high enantioselectivity, E/Z‐selectivity, and regioselectivity. The method exhibits broad functional group tolerance, and E/Z‐alkene mixtures are suitable C−H substrates. The transformation is enabled by light irradiation, which sustains the enantioselective copper catalysis by photoinduced oxidant homolysis.

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.

Advances in the Intermolecular Asymmetric Allylic Functionalization of Unreactive Acyclic Alkenes

Allylic C(sp3)−H functionalized architectures are not only widely present in natural products, pharmaceuticals, and functional organic materials, but also serve as versatile building blocks to furnish important functionalized molecules in synthetic chemistry. Accordingly, various strategies to access allylic functionalized alkenes in a stereoselective manner have been developed. However, chemo-, regio- and stereoselective intermolecular asymmetric allylic functionalization (AAF) of unreactive acyclic alkene (UAA) from readily available materials, representing a highly atom- and step-economic approach toward the generation of structural complexity, remains elusive and challenging. Herein, we review all intermolecular asymmetric catalyzed methods, with emphasis on the construction of chiral allylic units by activation of allylic C-H bonds of UAAs. Our analysis serves to document the considerable and rapid progress within the field, while also highlighting the limitations of current methods.

Rhodium-Catalyzed Highly Enantioselective Hydroboration of Acyclic Tetrasubstituted Alkenes Directed by an Amide.

Although progress has been made in enantioselective hydroboration of di- and trisubstituted alkenes over the past decades, enantioselective hydroboration of tetrasubstituted alkenes with high diastereo- and enantioselectivities continues as an unmet challenge since the 1950s due to its extremely low reactivity and the difficulties to simultaneously control the regio- and stereoselectivity of a tetrasubstituted alkene. Here, we report highly regio-, diastereo-, and enantioselective catalytic hydroboration of diverse acyclic tetrasubstituted alkenes. The delicate interplay of an electron-rich rhodium complex and coordination-assistance forms a highly adaptive catalyst that effectively overcomes the low reactivity and controls the stereoselectivity. The generality of the catalyst system is exemplified by its efficacy across various tetrasubstituted alkenes with diverse steric and electronic properties.

Catalyst/Metal/Solvent-Free Markovnikov Hydrothiolation of Unactivated Alkenes with Dithiocarbamic Acids.

Catalyst-free Markovnikov-selective hydrothiolation of unactivated alkenes still remains a great challenge. Herein, we develop a catalyst/metal/solvent-free methodology for the Markovnikov hydrothiolation of unactivated alkenes with in situ prepared dithiocarbamic acids, providing a wide array of alkyl dithiocarbamates. A variety of terminal, internal, cyclic, and acyclic unactivated alkenes were applied successfully in this protocol. This three-component thiol-ene reaction can be considered as a new family of click reactions.

2,2'-Bipyridine-Enabled Photocatalytic Radical [4+2] Cyclization of N-Aryl-α-amino Acids for Synthesizing Polysubstituted Tetrahydroquinolines.

A facile photocatalytic radical [4+2] cyclization of N-aryl-α-amino acids with various alkenes to access structurally polysubstituted tetrahydroquinolines has been developed. Using a simple bipyridine as a catalyst, different N-aryl-α-amino acids could be utilized as the radical precursors to react with diverse electrophilic alkenes, including exocyclic terminal alkenes, acyclic terminal alkenes, and cycloalkenes, producing 10 types of nitrogen-containing heterocyclic compounds fused in multiple frameworks in generally moderate yields with good diastereoselectivities. Scale-up synthesis and transformations of the products further demonstrated the synthetic application of this protocol. Moreover, a decarboxylative radial pathway via a proton-coupled electron transfer process for illustration of this [4+2] cyclization was proposed on the basis of the control experiments. This process is highlighted by a simple bipyridine photocatalysis, mild reaction conditions, various N-aryl-α-amino acids and alkene materials, and application for the modification of natural products.

The Electrochemical trans-Chloroformyloxylation of Unactivated Alkenes

AbstractAn attempted aryl selenium-catalyzed formation of cis-chlorohydrins from alkenes was unsuccessful but led to an electrochemical investigation for the trans-selective chloroformyloxylation of cyclic and acyclic alkenes in moderate to good yields. Interestingly, when 1,1-disubstituted alkenes were used, the corresponding vinyl chloride derivatives were obtained, and the application of 1-phenylcyclohex-1-ene led to the formation of an allyl chloride derivative.

Atroposelective Construction of Tetrasubstituted Axially Chiral Alkene Frameworks

AbstractThe construction of axially chiral alkene frameworks is currently one of hottest topics in the field of organic synthetic chemistry. Compared to traditional axially chiral molecules, such as biaryls, heterobiaryls, and anilides, the synthesis of axially chiral alkenes is far more challenging, especially for acyclic tetrasubstituted alkene analogues. In this review, we summarized the development of strategies for the synthesis of tetrasubstituted axially chiral alkene analogues, including asymmetric difunctionalization, C–H functionalization, cross-coupling, (dynamic) kinetic resolution, and asymmetric allylic substitution-isomerization.1 Introduction2 Synthesis of Cyclic Tetrasubstituted Axially Chiral Alkenes3 Synthesis of Acyclic Tetrasubstituted Axially Chiral Alkenes4 Summary and Outlook

Recent Approaches in Transition Metal-Catalyzed Chalcogenative Heteroannulation of Alkenes and Alkynes

Organochalcogen-bearing heterocycles are important scaffolds in compounds under the spotlight of scientific interest in optoelectronic fields and for biological applications. The use of transition metals has been a versatile and reliable way to carry out the synthesis of these molecules efficiently, delivering products in high yields and with a wide functional diversity. In the last 10 years, many classes of heterocycles have been synthesized under the cyclization reaction of acyclic alkenes and alkynes with the incorporation of a chalcogen atom on its structure. Transition metal catalysts including Cu, Co, Pd, Ni, In, Ag, and Fe salts have been used in the development of new methodologies, the expansion of substrate scope, and mechanistic studies. This review provides an overview of these recent approaches with the aim of being a useful resource for interested researchers in this area.

Iodination-Group-Transfer Reactions to Generate Trisubstituted Iodoalkenes with Regio- and Stereochemical Control.

The regio- and stereodefined synthesis of trisubstituted alkenes remains a significant synthetic challenge. Herein, a method is developed for producing regio- and stereodefined trisubstituted iodoalkenes by diverting intermediates from an iodination-electrophilic-cyclization mechanism. Specifically, cyclized sulfonium ion-pair intermediates are diverted to alkenes by ring-opening with nucleophilic iodide. Alternatively, scavenging of the iodide by AgOTf prevents ring-opening, enabling isolation of the sulfonium ion-pair intermediate. Isolation of the ion pair enables access to complementary reactivity, including ring-opening by alternative nucleophiles (i.e., amines), yielding trisubstituted acyclic alkenes and an example acyclic tetrasubstituted alkene. X-ray crystallographic determination of reaction intermediates and products confirms that the initial electrophilic-cyclization step sets the stereo- and regiochemistry of the product. The products serve as synthetic building blocks by readily participating in downstream functionalization reactions, including oxidation, palladium-catalyzed cross-coupling, and nucleophilic displacement.

Gas Chromatography-Mass Spectroscopy(GC-MS) of Chloroform Extract of Ficus exasperata Vahl

Gas Chromatography-Mass Spectrometry (GCMS) analysis of chloroform leaves extract of Ficus exasperate Vahl was performed to identify the composition and percentage abundance of the various phytochemical constituents of Ficus exasperate Vahl. The extract was obtained by fractionating methanol crude leave extract of Ficus exasperate Vahl with in order of increasing polarity, n-Hexane then chloroform. GC-MS analysis was carried out on a GC system comprising a Gas Chromatograph interfaced to a Mass Spectrometer (GC-MS) instrument. The components were compared with the database of spectrum of known components stored in the gas chromatography-mass spectrometry library. Gas Chromatography-Mass Spectrometry analysis of the chloroform leave extract of Ficus exasperate revealed the presence of acyclic olefin which is used for tanning oils and in synthetic fatty acids, Isopryl myristate used in cosmetics, Dibutyl phthalate which is used in cosmetics, textile, safety glass additive, oleic acid used in pharmaceuticals, Cyclopropanecarboxylic acid, 3-(2,2-dichlor used in agrochemicals and pharmaceuticals. The presence of these compounds justifies the use of some parts of the plant for various elements in folklore and can be advised as a plant of phytopharmaceutical and industrial importance.

Asymmetric Epoxidation of Alkenes Catalyzed by a Cobalt Complex.

Asymmetric epoxidation of alkenes catalyzed by nonheme chiral Mn-O and Fe-O catalysts has been well established, but chiral Co-O catalysts for the purpose remain virtually undeveloped due to the oxo wall. Herein is first reported a chiral cobalt complex to realize the enantioselective epoxidation of cyclic and acyclic trisubstituted alkenes by using PhIO as the oxidant in acetone, wherein the tetra-oxygen-based chiral N,N'-dioxide with sterically hindered amide subunits plays a crucial role in supporting the formation of the Co-O intermediate and enantioselective electrophilic oxygen transfer. Mechanistic studies, including HRMS measurements, UV-vis absorption spectroscopy, magnetic susceptibility, as well as DFT calculations, were carried out, confirming the formation of Co-O species as a quartet Co(III)-oxyl tautomer. The mechanism and the origin of enantioselectivity were also elucidated based on control experiments, nonlinear effects, kinetic studies, and DFT calculations.

Synthesis of Functionalized Tetrahydroquinoline Containing Indole Scaffold via Chemoselective Annulation of Aza-ortho-quinone Methide Precursor.

The chemoselective annulation of aza-ortho-quinone methide generated by in situ o-chloromethyl sulfonamide has been achieved with bifunctional acyclic olefin. This efficient approach provides access to the diastereoselective synthesis of functionalized tetrahydroquinoline derivatives containing indole scaffolds through the inverse-electron-demand aza-Diels-Alder reaction under mild reaction conditions with excellent results (up to 93% yield, > 20:1 dr). Moreover, this article realized the cyclization of α-halogeno hydrazone with electron-deficient alkene affording the tetrahydropyridazine derivatives, which had never been reported.

Thermally Robust and Highly Active PCP Cobalt(II) Catalyst for Linear-Selective Hydroboration of Terminal and Internal Olefins

We report the design and synthesis of cobalt complexes of L2X-type ligands for olefin hydroboration guided by the consideration of catalyst stability. Among the series of PCP-ligated Co(II) and Co(III) pincer complexes, the complex with iPr phosphino substituents exhibits broad scope, high functional group tolerance, and high catalytic activity at ppm catalyst loadings (17 ppm, 0.001 mol %) in the hydroboration of terminal olefins with pinacolborane (HBpin), furnishing anti-Markovnikov addition products. We also show that linear-selective hydroboration occurs with internal acyclic olefins at elevated temperatures, including those conjugated with the arene or carbonyl groups that are difficult to be achieved by previous catalysts. Such a catalytic property makes this cobalt catalyst suitable for terminally selective formal borylation of arylalkane through the dehydrogenation–hydroboration sequence. Experimental mechanistic data provide evidence for the involvement of a Co(II) hydride intermediate. Deuterium-labeling experiments show that the formation of terminal alkylboronate ester from internal olefins likely proceeds via the initial generation of secondary alkyl species, followed by chain-walking to form primary alkyl species, which then reacts with HBpin to produce the linear product and regenerate the hydride species.

Stereospecific Synthesis of Unprotected, α,β-Disubstituted Tryptamines and Phenethylamines from 1,2-Disubstituted Alkenes via a One-Pot Reaction Sequence.

Unprotected, α,β-disubstituted tryptamines and phenethylamines are obtained by a one-pot, metal-free sequence that proceeds by the in situ formation of aziridinium salts followed by Friedel-Crafts reaction with electron-rich (hetero)arenes. Both steps are facilitated by hexafluoroisopropanol as the solvent. The one-pot sequence was effective for diversely substituted indoles and 1,3,5-trimethoxybenzene, for cyclic and acyclic alkenes, and proceeded in a stereospecific fashion for both (E)- and (Z)-1,2-disubstituted alkenes. Moreover, one-pot morpholine addition to an aziridinium salt provided a diamine.

Exploring the influence of rigid carbocycles on terpenoid copolymer properties

AbstractSynthesizing soft polymers with uncommon architectural elements is critical for enhancing our understanding of fundamental structure–property relationships in macromolecules. Terpenoid materials are interesting candidates for addressing this grand challenge, as their constituent monomers can exhibit a diverse array of structural and functional groups. Moreover, these biologically‐derived materials can potentially expand the sphere of knowledge surrounding trends in related petrochemically‐derived polymers. For example, vinyl‐addition copolymers of norbornene and acyclic olefins can exhibit predictable properties (e.g., linear changes in Tg as a function of composition). Due to synthetic limitations, however, it is not well understood if other rigid carbocycles engender similar behavior in a range of copolymers. As numerous terpene scaffolds display rigid motifs (such as pinane systems), terpenoid polymers are uniquely positioned to address this deficiency. Here, we report the synthesis and characterization of terpenoid copolymers (both statistical and block) with systematically tailored compositions of pinene‐based comonomers. We found that the pinane core (which is a constitutional isomer of norbornene) appears to promote ideal behavior with regard to bulk thermal properties of statistical copolymers, which mirrors the behavior of norbornene‐based systems. We also found that block copolymers exhibited thermomechanical properties that were highly tunable (and apparently correlated to carbocycle composition).