Alkene Precursors Research Articles

(XantPhos)AgBr as a cheap and readily available catalyst for the bromofluorocyclopropanation of electron-rich alkenes

A silver phosphine complex (XantPhos)AgBr proved to be a cheap and readily accessible catalyst for bromofluoro- cyclopropanation of electron-rich alkenes with CFBr2CO2Na. Ozonolysis followed by treatment with NaHSO3 was shown to be an effective protocol to purify gem-bromofluoro- cyclopropanes from unreacted alkene precursors.

Manganese/Enzyme Sequential Catalytic Pathway for the Production of Optically Active γ-Functionalized Alcohols.

A brief, practical catalytic process for the production of optically active γ-functionalized alcohols from relevant alkenes has been developed by using a robust Mn(III)/air/(Me2SiH)2O catalytic system combined with lipase-catalyzed kinetic resolution. This approach demonstrates exceptional tolerance toward proximal functional groups present on alkenes, enabling the achievement of high yields and exclusive enantioselectivity. Under this sequential catalytic system, the chiral alkene precursors can also be converted into γ-functionalized alcohols and related acetates as separable single enantiomers.

Recent Synthesis of Nucleoside Phosphonate Analogs Using Olefin Cross-metathesis.

Nucleotide analogs known as acyclic and cyclic nucleoside phosphonates (ANPs and CNPs, respectively) have a variety of biological properties, including antibacterial, antiviral, antiparasitic, antineoplastic, and immunomodulatory. A strong reaction that has emerged in the last several decades has fundamentally changed our knowledge of the chemistry of nucleoside phosphonates. In particular, Olefin cross-metathesis (CM) has been a potent and practical synthesis route to produce functionalized olefins from essential alkene precursors. This review describes recent synthesis examples of ANPs and CNPs analogs using the Ru-catalyzed olefin cross-metathesis reactions. Olefin cross-metathesis reactions are performed in the olefinic parts of nucleoside and phosphonate produced by Grubbs, Hoveyda-Grubbs, and Nolan. This review presents a synthetic overview of a few chosen nucleosides with biological significance. Their biological activity results are briefly discussed.

Tetraethylammonium Salts as Solid, Easy to Handle Ethylene Precursors and Their Application in Mizoroki-Heck Coupling.

In this study, we introduce a convenient Heck vinylation protocol that eliminates the requirement for ethylene gas as a coupling partner. In contrast to traditional methodologies, quaternary ammonium salts can serve as solid olefin precursors under ambient atmosphere conditions. The practicality of this method, distinguished by its convenience and safety in a one-pot reaction, renders it appealing for applications in research and discovery context.

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.

Iridium complexes of acridine-based PNP-type pincer ligands: Synthesis, structure and reactivity

Acridine-based PNP-type pincer ligands (AcrPNP) have previously been used for the construction of a small number of Ru(II), Mn(I), Rh(III) and Ir(III) complexes, with most attention being given to the catalytically-active ruthenium complexes. In the present work, we significantly expand the scope of known AcrPNP complexes by introducing a series of new Ir(I) and Ir(III) complexes. These were synthesized from two AcrPNP ligands differing in their P-substituents (iPr vs Ph), in conjunction with various Ir(I)-olefin precursors, through different sequences of reactions that include intramolecular CH activations and additions of H2 and NaBEt3H. The new iridium complexes, with their observed structures and reactivities, reflect the unique properties of the acridine-based PNP ligands, i.e., their inherent structural flexibility and ability to support both metal-centered reactivity (CH and HH oxidative addition) and ligand-centered reactivity (hydride- and H2-induced dearomatization).

NiH-Catalyzed Functionalization of Remote and Proximal Olefins: New Reactions and Innovative Strategies.

Transition metal hydride catalyzed functionalization of remote and proximal olefins has many advantages over conventional cross-coupling reactions. It avoids the separate, prior generation of stoichiometric amounts of organometallic reagents and the use of preformed organometallic reagents, which are sometimes hard to access and may compromise functional group compatibility. The migratory insertion of metal hydride complexes generated in situ into readily available alkene starting materials, the hydrometalation process, provides an attractive and straightforward route to alkyl metal intermediates, which can undergo a variety of sequential cross-coupling reactions. In particular, with the synergistic combination of chain-walking and cross-coupling chemistry of nickel, NiH-catalyzed functionalization of remote and proximal olefins has undergone particularly intense development in the past few years. This Account aims to chronicle the progress made in this arena in terms of activation modes, diverse functionalizations, and chemo-, regio-, and enantioselectivity.We first provide a brief introduction to the general reaction mechanisms. Taking remote hydroarylation as an example, the four oxidation states of Ni have allowed us to develop two different reaction strategies to form the final product: a Ni(I)-H/X-Ni(II)-H platform that relies on stoichiometric reductants and a Ni(I/II/III) cycle and a redox-neutral functional group or FG-Ni(II)-H platform that reacts with an alkene substrate and forms the migratory products via a Ni(0/II) pathway. We also demonstrate that diverse functionalization, including general C-C bond-forming reactions and the more challenging C-N/C-S bond-forming reactions could be realized. Moreover, the employment of appropriate chiral ligands has allowed us to successfully realize the corresponding asymmetric hydrofunctionalization reactions of olefins, including hydroalkylation, hydroarylation, hydroalkenylation, hydroalkynylation, and hydroamination. Interestingly, the enantio-determining step could be enantioselective hydronickelation, selective oxidative addition, or selective reductive elimination. To realize more challenging asymmetric migratory hydrofunctionalization, we have developed a general ligand relay catalytic strategy with a combination of two simple ligands, the first for chain-walking and the second for asymmetric coupling. This novel strategy avoids the design of a single, possibly structurally complex chiral ligand to promote both steps of chain-walking and asymmetric coupling. In addition, the success of multicomponent hydrofunctionalization provides a convenient approach to gain simple access to complex molecules. Finally, alkyl halides could be used as olefin precursors to undergo a variety of reductive migratory cross-electrophile coupling reactions. Applications of these remote hydrofunctionalization reactions are also discussed. We hope this Account will inspire future development in the field to overcome key challenges, including conceptually new catalytic strategies, development of high-performance systems with enhanced reactivity and selectivity, cutting-edge catalyst design, and further mechanistic studies.

σ-Alkynyl Adsorption Enables Electrocatalytic Semihydrogenation of Terminal Alkynes with Easy-Reducible/Passivated Groups over Amorphous PdSx Nanocapsules.

Highly chemo- and regioselective semihydrogenation of alkynes is significant and challenging for the synthesis of functionalized alkenes. Here, a sequential self-template method is used to synthesize amorphous palladium sulfide nanocapsules (PdSx ANCs), which enables electrocatalytic semihydrogenation of terminal alkynes in H2O with excellent tolerance to easily reducible groups (e.g., C-I/Br/Cl, C═O) and the metal center deactivating skeletons (e.g., quinolyl, carboxyl, and nitrile). Mechanistic studies demonstrate that specific σ-alkynyl adsorption via terminal carbon and negligible alkene adsorption on isolated Pd2+ sites ensure successful synthesis of various alkenes with outstanding time-irrelevant selectivity in a wide potential range. The key hydrogen and carbon radical intermediates are validated by electron paramagnetic resonance and high-resolution mass spectrometry. Gram-scale synthesis of 4-bromostyrene and expedient preparation of deuterated alkene precursors and drugs with D2O show promising applications. Impressively, PdSx ANCs can be applied to the prevailing thermocatalytic semihydrogenation of functionalized alkyne using H2.

Selectfluor Mediated Difunctionalization of Olefins towards the Synthesis of Fluoromethylated Morpholines

A Selectfluor-mediated synthesis of monofluoromethylated morpholines has been developed via the oxyfluorination of N-allylated aminoalcohols. This olefin difunctionalization strategy provides an access to a new chemical space utilizing readily available starting materials, exhibits good functional group compatibility, and can be performed on a gram scale.

Development of an Operationally Simple, Scalable, and HCN-Free Transfer Hydrocyanation Protocol Using an Air-Stable Nickel Precatalyst

Hydrocyanation reactions enable access to synthetically valuable nitriles from readily available alkene precursors. However, hydrocyanation reactions using hydrogen cyanide (HCN) or similarly toxic reagents on laboratory scale can be particularly challenging due to their hazardous nature. In addition, such processes typically require air- and temperature-sensitive Ni(0) precatalysts, further reducing the operational simplicity of this transformation. Herein, we report a HCN-free transfer hydrocyanation of alkenes and alkynes that employs commercially available aliphatic nitriles as sacrificial HCN donors in combination with a catalytic amount of air-stable and inexpensive NiCl2 as a precatalyst and a cocatalytic Lewis acid. The scalability and robustness of the catalytic process were demonstrated by the hydrocyanation of α-methylstyrene on a 100 mmol scale (11.4 g of product obtained) using 1 mol % of the Ni catalyst. In addition, the feasibility of the dehydrocyanation protocol using the air-stable Ni(II) precatalyst and norbornadiene as a sacrificial acceptor was showcased by the selective conversion of an aliphatic nitrile into the corresponding alkene.

Synthesis and mesomorphic properties of new organosiloxane chiral calamitic liquid crystals

A new chiral calamitic compound consisting of a phenyl core that is connected through ester linkers to a benzoate carrying a chiral (S)-2-methylbutoxy group at one side and a biphenyl carboxylate with an undecenyloxy chain at other side has been synthesized. Additionally, the siloxane substituted derivatives and a dimer with these two identical chiral calamitics linked by a disiloxane spacer have been obtained via hydrosilylation reaction to study the effect of combining the chiral moiety and siloxane segments within the same structure on liquid crystalline properties. The chiral calamitic compound and derivatives with a siloxane end-group or a siloxane spacer have been characterized using classical spectroscopic methods (1H NMR, 13C NMR, 29Si NMR and MS) and elemental analysis (EA). The liquid crystalline properties of all new compounds were investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray scattering and electro-optic methods. With the introduction of a siloxane end-group to the vinyl-terminated calamitic compound exhibiting enantiotropic chiral nematic phase (N*) and chiral tilted smectic phase (SmC*), the occurrence of stable smectic phase was strongly promoted. In a similar way, the dimer with two identical calamitic mesogens connected by a disiloxane spacer exhibited a wider smectic mesophase interval in addition to the presence of N* mesophase. The new mesogens exhibit a ferroelectric switching with PS of around 200 nC cm−2 in their chiral tilted smectic (SmC*) mesophase range. The transition temperatures of organosiloxanes are considerably lower than that of olefinic precursor.

A Review on Olefin Metathesis Reactions as a Green Method for the Synthesis of Organic Compounds

Olefin metathesis is a metal-mediated C-C bond exchange by which the two fragments within the olefin precursor are redistributed as a result of breaking the double bond to obtain a new product. Currently, most of the synthetic organic compounds, polymers, drugs, plastics, and other synthetic materials are synthesized via the application of olefin metathesis reactions. In this review, different types of olefin metathesis reactions with their plausible mechanisms and their application in synthetic organic chemistry have been discussed.

A stable diazoalkene

Organic Chemistry Modern organic chemistry has produced such a large array of intricately complex products that it is easy to forget the simple motifs that have eluded bulk synthesis. One such case is the diazoalkene, an unsaturated variant of the more common diazoalkanes. Consisting of three adjacent double bonds (C=C=N=N), this fragment is of particular interest as a precursor to reactive vinylidenes. Antoni et al. report the preparation of an N-heterocycle–substituted diazoalkene by oxidation of an olefinic precursor with nitrous oxide. The compound is stable in solid and solution states under inert atmosphere and reacts cleanly with isocyanides. Nat. Chem. 13 , 587 (2021).

General Mechanism for Sulfate Radical Addition to Olefinic Volatile Organic Compounds in Secondary Organic Aerosol.

Previous laboratory studies have suggested that sulfate radical addition to olefinic biogenic volatile organic compounds (BVOCs) is a potential formation mechanism for some organosulfates detected in ambient secondary organic aerosol (SOA). However, these studies propose conflicting reaction products, possibly because laboratory dissolved oxygen levels did not accurately reflect atmospheric conditions. Additionally, these studies used analytical methods that could not definitively identify and quantify the structurally specific products. Here, we describe a method that allows for the study of the reaction of sulfate radicals and several olefinic precursors, including allyl alcohol (AA), methyl vinyl ketone (MVK), 2-methyl-3-buten-2-ol (MBO), and methacrolein (MA), with careful control of dissolved oxygen levels and using the isomer-specific nuclear magnetic resonance (NMR) method to definitively identify and quantify the reaction products. Specific mechanisms for each olefinic precursor were developed, as well as a generalized mechanism that can be used to predict the sulfate radical reaction pathways for any olefin. The product yield results indicate that this mechanism is dominated by carbon backbone fragmentation pathways: 61, 83, 79, and 100% for AA, MVK, MBO, and MA, respectively. Several of the observed organosulfate products have also been detected in field observations of SOA, which indicates the potential relevance of this mechanism in the atmosphere.

Visible-Light-Enabled Aerobic Denitrative C3-Alkenylation of Indoles with β-Nitrostyrenes

Herein, we unveil the first visible-light-mediated alkenylation reaction of indoles. The reaction follows a denitrative radical pathway where β-nitrostyrenes have been utilized as the alkene precursors for the C3-styrenylation of indoles under visible-light irradiation to afford biologically and synthetically important 3-alkenylindoles. High regioselectivity, absence of any photocatalyst, metal, external oxidant, acid or base, and the use of visible light and air as inexpensive clean reagents are the key highlights of the developed method.

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes.

This paper describes the synthesis of a series of organic liquid crystals (LCs) containing selectively fluorinated cyclopropanes at their termini. The syntheses used difluorocarbene additions to olefin precursors, an approach which proved straightforward such that these liquid crystal candidates could be efficiently prepared. Their physical and thermodynamic properties were evaluated and depending on individual structures, they either displayed positive or negative dielectric anisotropy. The study gives some guidance into effective structure–property relationships for the design of LCs containing selectively fluorinated cyclopropane motifs.

Indandione-Terminated Quinoids: Facile Synthesis by Alkoxide-Mediated Rearrangement Reaction and Semiconducting Properties.

A series of 1,3-indandione-terminated π-conjugated quinoids were synthesized by alkoxide-mediated rearrangement reaction of the respective alkene precursors, followed by air oxidation. This new protocol allows access to quinoidal compounds with variable termini and cores. The resulting quinoids all show LUMO levels below -4.0 eV and molar extinction coefficients above 105 L mol-1 cm-1 . The optoelectronic properties of these compounds can be regulated by tuning the central cores as well as the aryl termini ascribed to the delocalized frontier molecular orbitals over the entire molecular skeleton involving aryl termini. n-Channel organic thin-film transistors with electron mobility of up to 0.38 cm2 V-1 s-1 were fabricated, showing the potential of this new class of quinoids as organic semiconductors.

Indandione‐Terminated Quinoids: Facile Synthesis by Alkoxide‐Mediated Rearrangement Reaction and Semiconducting Properties

AbstractA series of 1,3‐indandione‐terminated π‐conjugated quinoids were synthesized by alkoxide‐mediated rearrangement reaction of the respective alkene precursors, followed by air oxidation. This new protocol allows access to quinoidal compounds with variable termini and cores. The resulting quinoids all show LUMO levels below −4.0 eV and molar extinction coefficients above 105 L mol−1 cm−1. The optoelectronic properties of these compounds can be regulated by tuning the central cores as well as the aryl termini ascribed to the delocalized frontier molecular orbitals over the entire molecular skeleton involving aryl termini. n‐Channel organic thin‐film transistors with electron mobility of up to 0.38 cm2 V−1 s−1 were fabricated, showing the potential of this new class of quinoids as organic semiconductors.

1,2-Boron Shifts of β-Boryl Radicals Generated from Bis-boronic Esters Using Photoredox Catalysis.

1,2-Bis-boronic esters are versatile intermediates that enable the rapid elaboration of simple alkene precursors. Previous reports on their selective mono-functionalization have targeted the most accessible position, retaining the more hindered secondary boronic ester. In contrast, we have found that photoredox-catalyzed mono-deboronation generates primary β-boryl radicals that undergo rapid 1,2-boron shift to form thermodynamically favored secondary radicals, allowing for selective transformation of the more hindered boronic ester. The pivotal 1,2-boron shift, which has been demonstrated to be stereoretentive, enables access to a wide range of functionalized boronic esters and has been applied to highly diastereoselective fragmentation and transannular cyclization reactions. Furthermore, its generality has been shown in a radical cascade reaction with an allylboronic ester.

Tunable Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbons by General One-Pot C-H Borylations.

Boron-doping has long been recognized as a promising LUMO energy-lowering modification of graphene and related polycyclic aromatic hydrocarbons (PAHs). Unfortunately, synthetic difficulties have been a significant bottleneck for the understanding, optimization, and application of precisely boron-doped PAHs for optoelectronic purposes. Herein, a facile one-pot hydroboration electrophilic borylation cascade/dehydrogenation approach from simple alkene precursors is coupled with postsynthetic B-substitution to give access to ten ambient-stable core- and periphery-tuned boron-doped PAHs. These include large hitherto unknown doubly boron-doped analogues of anthanthrene and triangulene. Crystallographic, optical, electrochemical, and computational studies were performed to clarify the effect of boron-doped PAH shape, size, and structure on optoelectronic properties. Our molecular tuning allowed the synthesis of molecules exhibiting visible-range absorption, near-unity fluorescence quantum yields, and, to our knowledge, the most facile electrochemical reductions of any reported ambient-stable boron-doped PAHs (corresponding to LUMO energy levels as low as fullerenes). Finally, our study describes the first implementation of a precise three-coordinate boron-substituted PAH as an acceptor material in organic solar cells with power conversion efficiencies (PCEs) of up to 3%.