Showing papers on "Double bond published in 2020"
TL;DR: This review summarizes the advances in transition-metal-catalyzed cross-coupling via carbon-sulfur bond activation and cleavage since late 2012 as an update of the critical review on the same topic published in early 2013.
Abstract: Carbon-sulfur bond cross-coupling has become more and more attractive as an alternative protocol to establish carbon-carbon and carbon-heteroatom bonds. Diverse transformations through transition-metal-catalyzed C-S bond activation and cleavage have recently been developed. This review summarizes the advances in transition-metal-catalyzed cross-coupling via carbon-sulfur bond activation and cleavage since late 2012 as an update of the critical review on the same topic published in early 2013 (Chem. Soc. Rev., 2013, 42, 599-621), which is presented by the categories of organosulfur compounds, that is, thioesters, thioethers including heteroaryl, aryl, vinyl, alkyl, and alkynyl sulfides, ketene dithioacetals, sulfoxides including DMSO, sulfones, sulfonyl chlorides, sulfinates, thiocyanates, sulfonium salts, sulfonyl hydrazides, sulfonates, thiophene-based compounds, and C[double bond, length as m-dash]S functionality-bearing compounds such as thioureas, thioamides, and carbon disulfide, as well as the mechanistic insights. An overview of C-S bond cleavage reactions with stoichiometric transition-metal reagents is briefly given. Theoretical studies on the reactivity of carbon-sulfur bonds by DFT calculations are also discussed.
137 citations
01 Jan 2020
TL;DR: In this article, the authors demonstrate that the organization of the reacting species in microstructured, aqueous solutions allows generation of carbon-centred radicals from non-activated alkyl chlorides in the presence of double bonds via assembly-promoted single electron transfer.
Abstract: Photoredox catalysis has developed into a powerful tool for the synthesis of organic compounds with diverse structures. However, stable carbon–chloride bonds remain beyond the energetic limits of the outer-sphere photoreductive activation. Here, we demonstrate that the organization of the reacting species in microstructured, aqueous solutions allows generation of carbon-centred radicals from non-activated alkyl chlorides in the presence of double bonds via assembly-promoted single electron transfer. Photocatalytic systems consisting of a surfactant, organic substrates and additives have been designed, characterized and applied for radical dechlorination, addition and cyclization reactions. Cheap and commercially available blue light-emitting diodes are used as the irradiation source for the transformations. Mechanistic studies indicate the accumulation of the energy of two visible light photons in one catalytic cycle. Photocatalytic activation of alkyl carbon–chlorine bonds has constantly proven difficult due to the high energies needed to cleave this stable bond. Here a surfactant-based photocatalytic system is used, allowing for the radical dehalogenation and subsequent reactivity of unactivated alkyl chlorides.
128 citations
TL;DR: The rapid switch-on/off electro-epoxidation of a single sample, the low sample consumption, the demonstrated applicability to complex lipids containing multiple double bonds, and no need for any extra apparatus should allow this method to be widely used in lipid related biological studies.
Abstract: Reported here is the first on-demand electrochemical epoxidation incorporated into the standard nano-electrospray ionization mass spectrometry (nanoESI-MS) workflow for double-bond identification. The capability lies in a novel tunable electro-epoxidation of double bonds, where onset of the reaction can be controlled by simply tuning the spray voltage. On-demand formation of mono-/multiple epoxides is achieved at different voltages. The electro-epoxidized products are then fragmented by tandem MS to generate diagnostic ions, indicating the double bond position(s). The process is completed within seconds, holding great potential for high-throughput analysis. The rapid switch-on/off electro-epoxidation of a single sample, the low sample consumption, the demonstrated applicability to complex lipids containing multiple double bonds, and the advantage of not requiring extra apparatus make this method attractive for use in lipid-related biological studies.
75 citations
TL;DR: A novel reaction of diazo compounds utilizing a radical-mediated addition strategy to achieve difunctionalization of diverse alkenes is reported, which is highly complementary, proceed under mild reaction conditions, and show high functional group tolerance.
Abstract: One of the most common reactions of diazo compounds with alkenes is cyclopropanation, which occurs through metal carbene or free carbene intermediates. Alternative functionalization of alkenes with diazo compounds is limited, and a methodology for the addition of the elements of Z-CHR2 (with Z = H or heteroatom, and CHR2 originates from N2═CR2) across a carbon-carbon double bond has not been reported. Here we report a novel reaction of diazo compounds utilizing a radical-mediated addition strategy to achieve difunctionalization of diverse alkenes. Diazo compounds are transformed to carbon radicals with a photocatalyst or an iron catalyst through PCET processes. The carbon radical selectively adds to diverse alkenes, delivering new carbon radical species, and then forms products through hydroalkylation by thiol-assisted hydrogen atom transfer (HAT), or forms azidoalkylation products through an iron catalytic cycle. These two processes are highly complementary, proceed under mild reaction conditions, and show high functional group tolerance. Furthermore, both transformations are successfully performed on a gram-scale, and diverse γ-amino esters, γ-amino alcohols, and complex spirolactams are easily prepared with commercially available reagents. Mechanistic studies reveal the plausible pathways that link the two processes and explain the unique advantages of each.
63 citations
TL;DR: A highly selective nickel-catalyzed four-component carbocarbonylation of alkenes under one atmosphere (1 atm) of CO gas to efficiently achieve an array of complex carbonyl compounds, including fluorinated amino acids and oligopeptides of great interest in medicinal chemistry and chemical biology.
Abstract: Transition-metal-catalyzed carbonylation is one of the most straightforward strategies to prepare carbonyl compounds. However, compared to well-established noble-metal-catalyzed carbonylation reactions, analogue coupling via base-metal, nickel catalysis has received less attention because of the easy formation of highly toxic and unreactive Ni(CO)4 species between Ni(0) and CO. To date, the use of inexpensive and widely available carbon monoxide (CO) gas for nickel-catalyzed carbonylation reaction remains challenging, and nickel-catalyzed four-component carbonylative reaction has not been reported yet. Here, we report a highly selective nickel-catalyzed four-component carbocarbonylation of alkenes under 1 atm (1 atm) of CO gas to efficiently achieve an array of complex carbonyl compounds, including fluorinated amino acids and oligopeptides of great interest in medicinal chemistry and chemical biology. This reaction relies on a nickel-catalyzed one-pot cascade process to assemble CO, arylboronic acids, and difluoroalkyl electrophiles across the carbon-carbon double bond of alkenes, paving a new way for base-metal-catalyzed carbonylative cascade reaction.
62 citations
TL;DR: A cobalt-catalyzed chain-walking double hydroboration of 1,n-dienes to access gem-bis(boryl)alkanes with regioselective control is shown, which allows the selective production of a single organoboron product in particular, for a broad scope of dienes.
Abstract: Double hydroboration of dienes is the addition of a hydrogen and a boryl group to the two double bonds of a diene molecule and represents a straightforward and effective protocol to prepare synthetically versatile bis(boryl)alkanes, provided that this reaction occurs selectively. However, this reaction can potentially yield several isomeric organoboron products, and it still remains a challenge to control the regioselectivity of this reaction, which allows the selective production of a single organoboron product, in particular, for a broad scope of dienes. By employing a readily available cobalt catalyst, here we show that this double hydroboration yields synthetically useful gem-bis(boryl)alkanes with excellent regioselectivity. In addition, the scope of dienes for this reaction is broad and encompasses a wide range of conjugated and non-conjugated dienes. Furthermore, mechanistic studies indicate that this cobalt-catalyzed double hydroboration occurs through boryl-directed chain-walking hydroboration of alkenylboronates generated from anti-Markovnikov 1,2-hydroboration of 1,n-diene. Control of regioselectivity in the double hydroboration of dienes to obtain a single organoboron compound is a considerable synthetic challenge. Here, the authors show a cobalt-catalyzed chain-walking double hydroboration of 1,n-dienes to access gem-bis(boryl)alkanes with regioselective control.
48 citations
TL;DR: This review describes the additions of allylMagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents.
Abstract: This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reage...
45 citations
TL;DR: A top-down shotgun-MS method utilizing gas-phase ion/ion charge inversion chemistry that provides near-complete GPL structural identification and was applied to the analysis of targeted GPL extracted from human plasma, including several proposed plasma biomarkers.
Abstract: Shotgun lipidomics has recently gained popularity for lipid analysis. Conventionally, shotgun analysis of glycerophospholipids via direct electrospray ionization tandem mass spectrometry (ESI-MS/MS) provides glycerophospholipid (GPL) class (i.e., headgroup composition) and fatty acyl composition. Reliant on low-energy collision-induced dissociation (CID), traditional ESI-MS/MS fails to define fatty acyl regiochemistry along the glycerol backbone or carbon-carbon double bond position(s) in unsaturated fatty acyl substituents. Therefore, isomeric GPLs are often unresolved, representing a significant challenge for shotgun-MS approaches. We developed a top-down shotgun-MS method utilizing gas-phase ion/ion charge inversion chemistry that provides near-complete GPL structural identification. First, in negative ion mode, CID of mass-selected GPL anions generates fatty acyl carboxylate anions via fragmentation of ester bonds linking the fatty acyl substituents at the sn-1 and sn-2 positions of the glycerol backbone. Product anions, including fatty acyl carboxylate ions, were then derivatized in the mass spectrometer via an ion/ion charge inversion reaction with tris-phenanthroline magnesium dications. Subsequent CID of charge-inverted fatty acyl complex cations yielded isomer-specific product ion spectra that permit (i) unambiguous assignment of carbon-carbon double bond position(s) and (ii) relative quantitation of isomeric fatty acyl substituents. The outlined strategy was applied to the analysis of targeted GPLs extracted from human plasma, including several proposed plasma biomarkers. A single experiment thus facilitates assignment of the GPL headgroup, fatty acyl composition, carbon-carbon double bond position(s) in unsaturated fatty acyl chains, and, in some cases, fatty acyl sn-position and relative abundances for isomeric fatty acyl substituents. Ultimately, this MSn platform paired with ion/ion chemistry permitted identification of major, and some minor, isomeric contributors that are unresolved using conventional ESI-MS/MS.
45 citations
TL;DR: It is shown that catalytic amounts of an appropriate earth-abundant iron-based complex, a base and a boryl compound promote efficient and controllable alkene transposition, and regiodivergent access to different products from one substrate can be facilitated.
Abstract: The catalytic isomerization of C-C double bonds is an indispensable chemical transformation used to deliver higher-value analogues and has important utility in the chemical industry. Notwithstanding the advances reported in this field, there is compelling demand for a general catalytic solution that enables precise control of the C═C bond migration position, in both cyclic and acyclic systems, to furnish disubstituted and trisubstituted alkenes. Here, we show that catalytic amounts of an appropriate earth-abundant iron-based complex, a base and a boryl compound, promote efficient and controllable alkene transposition. Mechanistic investigations reveal that these processes likely involve in situ formation of an iron-hydride species which promotes olefin isomerization through sequential olefin insertion/β-hydride elimination. Through this strategy, regiodivergent access to different products from one substrate can be facilitated, isomeric olefin mixtures commonly found in petroleum-derived feedstock can be transformed to a single alkene product, and unsaturated moieties embedded within linear and heterocyclic biologically active entities can be obtained.
43 citations
TL;DR: This review article focuses on reactivity of the terminal imido complexes of Group 4-6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination,Alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.
41 citations
TL;DR: The Cα–Cβ bond in homoallylic alcohols can be activated under basic conditions, qualifying these nonstrained acyclic systems as radical allylation reagents, and the role of base in the C–C bond activation is studied by computation.
Abstract: The Cα-Cβ bond in homoallylic alcohols can be activated under basic conditions, qualifying these nonstrained acyclic systems as radical allylation reagents. This reactivity is exemplified by photoinitiated (with visible light and/or blue LEDs) allylation of perfluoroalkyl and alkyl radicals generated from perfluoroalkyl iodides and alkylpyridinium salts, respectively, with homoallylic alcohols. C-radical addition to the double bond of the title reagents and subsequent base-promoted homolytic Cα-Cβ cleavage leads to the formation of the corresponding allylated products along with ketyl radicals that act as single electron reductants to sustain the chain reactions. Substrate scope is documented and the role of base in the C-C bond activation is studied by computation.
TL;DR: The authors show an enantioselective Si-C coupling by hydrosilylation of activated alkenes using a palladium/phosphoramidite catalyst affording axially chiral succinimides.
Abstract: Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. However, catalytic asymmetric hydrosilylation of activated alkenes and internal alkenes has proven elusive, due to competing reduction of carbon-carbon double bond or isomerization processes. Herein, we report a highly enantioselective Si-C coupling by hydrosilylation of carbonyl-activated alkenes using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand, which inhibits O-hydrosilylation/olefin reduction. The stereospecific Si-C coupling/hydrosilylation of maleimides affords a series of silyl succinimides with up to 99% yield, >99:1 diastereoselectivity and >99:1 enantioselectivity. The high degree of stereoselectivity exerts remote control of axial chirality, leading to functionalized, axially chiral succinimides which are versatile building blocks. The product utility is highlighted by the enantioselective construction of N-heterocycles bearing up to three stereocenters.
TL;DR: Phosphagallenes featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (NacNac=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2).
Abstract: Phosphagallenes (1 a/1 b) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6-i-Pr2 C6 H3 )]2 ). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a, which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound (2) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H2 and forms a 1:1 adduct with CO2 .
TL;DR: In this article, a biphasic model was proposed for the vegetable oil epoxidation with peracetic acid formed in situ in the presence of an ion exchange resin, taking into account the influence of the oil fatty acid composition, as an important property of this renewable raw material, on the kinetics of the process.
TL;DR: An on-tissue ozonization protocol is introduced that enables a particular straightforward derivatization of unsaturated lipids in tissue sections and highlights the potential of the technique to expose local isomer-specific metabolism of PLs.
Abstract: Visualizing the differential distribution of carbon-carbon double bond (C═C db) positional isomers of unsaturated phospholipids (PL) in tissue sections by use of refined matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) technologies offers a high promise to deeper understand PL metabolism and isomer-specific functions in health and disease. Here we introduce an on-tissue ozonization protocol that enables a particular straightforward derivatization of unsaturated lipids in tissue sections. Collision-induced dissociation (CID) of MALDI-generated ozonide ions (with yields in the several ten percent range) produced the Criegee fragment ion pairs, which are indicative of C═C db position(s). We used our technique for visualizing the differential distribution of Δ9 and Δ11 isomers of phosphatidylcholines in mouse brain and in human colon samples with the desorption laser spot size 15 μm, emphasizing the potential of the technique to expose local isomer-specific metabolism of PLs.
TL;DR: In this article, the synthesis of s-block metal complexes with a double-bond has been reported, but no s block metal complexes have been identified with the double bond.
TL;DR: This work finds that the ring-opened α- and β-pinene isomers as well as isomers of limonene and terpinolene have unimolecular reactions that are fast enough to likely dominate their reactivity under most atmospheric conditions.
Abstract: Monoterpenes are a group of volatile organic compounds (VOCs) emitted to the atmosphere in large amounts. Studies have linked the autoxidation of monoterpenes to the formation of secondary organic aerosols, which impact Earth's climate and human health. Here, we study the hydroxy peroxy radicals formed by OH- and O2-addition to the six atmospherically relevant monoterpenes α-pinene, β-pinene, Δ3-carene, camphene, limonene, and terpinolene. The six monoterpenes all have a six-membered ring but differ in the binding pattern of the four remaining carbon atoms and the position of the double bond(s). We use a multiconformer transition state theory approach to calculate the rate coefficients of the peroxy radical hydrogen-shift (H-shift) and endoperoxide formation reactions of these peroxy radicals. Our results suggest that primarily the isomers with a carbon-carbon double bond remaining after OH- and O2-addition undergo unimolecular reactions with rate coefficients large enough to be of atmospheric importance. This greatly limits the number of potentially important unimolecular pathways. Specifically, we find that the ring-opened α- and β-pinene isomers as well as isomers of limonene and terpinolene have unimolecular reactions that are fast enough to likely dominate their reactivity under most atmospheric conditions.
01 Apr 2020
TL;DR: In this article, an electron-deficient ketone catalyst was used to transfer nitrogen to unactivated carbon-carbon double-bonded olefins preferentially over activated C=C bonds.
Abstract: Organocatalytic nitrogen transfer to C=C bonds provides straightforward access to aziridines under mild conditions with low financial and environmental impacts; however, previous methods were typically limited to conjugated C=C bonds (that is, activated olefins), whereas aziridination of isolated C=C bonds (that is, unactivated olefins) remains underexplored. Here we demonstrate a strategy for nitrogen transfer to unactivated olefins by utilizing electron-deficient ketones as catalysts. An oxaziridine intermediate, generated in situ from the ketone catalyst and a nitrogen source, transfers nitrogen to unactivated C=C bonds preferentially over activated C=C bonds. This ‘unusual’ chemoselectivity, as well as the enantioselectivity realized through the use of a chiral ketone catalyst, cannot be achieved by previously developed methods that are based on either organocatalysts or metal catalysts. Moreover, mechanistic studies through modified mass spectrometry allow capture and further investigation of the transient oxaziridine intermediate, establishing its essential role in this nitrogen transfer process. There are very few methods for the organocatalytic aziridination of unactivated olefins. Here the authors report a simple ketone catalyst for the transfer of nitrogen to isolated carbon–carbon double bonds, with good substrate scope and in high yields.
TL;DR: It is clarified that the metal-centering octahedral pentazolate framework was entrapped by dual ionic-covalent bonds, which can effectively enhance the chemical insensitivity and thermal stability, further preventing the autodecomposition of monatomic solid N5- anions into dinitrogen.
Abstract: Stabilization of the pentazole anion only by acidic circumstances entrapment impedes the realization of a full-nitrogen substance; however, compression of nitrogen-rich nitrides has been recommend as an alternative way that has more controllable advantages to acquire the atomic nitrogen states. Through the structure searches are in conjunction with first-principle calculations, moderate pressure stabilized nitrogen-rich zinc nitrides with abundant extended nitrogen structures, e.g., cyclo-N5, infinite -(N4)n- chains, three-point stars N(N3), and N2 dumbbells, are predicted. The resonance between alternating σ bonds and π bonds in poly nitrogen sublattices takes charge of the coexistence of single and double bonds. The Zn(N5)2 salt has a noteworthy energy density (6.57 kJ/g) among the reported binary metal nitrides and synthesized pentazolate hydrates. An excellent Vicker's hardness (34 GPa) and detonation performance is unraveled. Although Zn(N5)2 salt is not expected to be recoverable at ambient conditions, it is worth noting that Zn(N5)2 is found to be stable at a very low pressure of ∼30 GPa, which is only half of those pressures required to synthesize CsN5. We clarified that the metal-centering octahedral pentazolate framework was entrapped by dual ionic-covalent bonds. More importantly, the covalent bonding can effectively enhance the chemical insensitivity and thermal stability, further preventing the autodecomposition of monatomic solid N5- anions into dinitrogen. Meanwhile, a unique topological pseudogap that attached to a metastable phase of ZnN4 salt is exposed for the first time, due to the dual effects of strong covalent sp2 hybridization interaction and the origin of ionic states.
TL;DR: The practical application of 193 nm UVPD-MS/MS is demonstrated via characterization of changes in the ratios of fatty acid double bond positional isomers in isogenic colorectal cancer cell lines.
Abstract: Fatty acids are a major source of structural diversity within the lipidome due to variations in their acyl chain lengths, branching, and cyclization, as well as the number, position, and stereochemistry of double bonds within their mono- and poly-unsaturated species. Here, the utility of 193 nm UltraViolet PhotoDissociation tandem mass spectrometry (UVPD-MS/MS) has been evaluated for the detailed structural characterization of a series of unsaturated fatty acid lipid species. UVPD-MS/MS of unsaturated fatty acids is shown to yield pairs of unique diagnostic product ions resulting from cleavages adjacent to their C=C double bonds, enabling unambiguous localization of the site(s) of unsaturation within these lipids. The effect of several experimental variables on the observed fragmentation behaviour and UVPD-MS/MS efficiency, including the position and number of double bonds, the effect of conjugated versus non-conjugated double bonds, the number of laser pulses, and the influence of alkali metal cations (Li, Na, K) as the ionizing adducts, has been evaluated. Importantly, the abundance of the diagnostic ions is shown to enable relative quantitation of mixtures of fatty acid isomers across a range of molar ratios. Finally, the practical application of 193 nm UVPD-MS/MS is demonstrated via characterization of changes in the ratios of fatty acid double bond positional isomers in isogenic colorectal cancer cell lines. This study therefore demonstrates the practicality of UVPD-MS/MS for the structural characterization of fatty acid isomers in lipidome analysis workflows.
TL;DR: The first example of a dearomative palladium-catalysed isocyanide insertion reaction has been developed using functionalized isochenides as the reaction partner of N-(2-bromobenzoyl)indoles.
TL;DR: In this paper, the effect of the topology and chemical composition of the zeolite on the purification of α-olefins was investigated and an effective potential for the cations with the double bond of the olefins were developed.
TL;DR: The use of Lewis and protic acids in different solvents has been studied to investigate the possible modulation of the reactivity of CBD (cannabidiol) and the complete NMR spectroscopic characterizations of the four isomers are reported.
Abstract: The chemical reactivity of cannabidiol is based on its ability to undergo intramolecular cyclization driven by the addition of a phenolic group to one of its two double bonds. The main products of this cyclization are Δ9-THC (trans-Δ-9-tetrahydrocannabinol) and Δ8-THC (trans-Δ-8-tetrahydrocannabinol). These two cannabinoids are isomers, and the first one is a frequently investigated psychoactive compound and pharmaceutical agent. The isomers Δ8-iso-THC (trans-Δ-8-iso-tetrahydrocannabinol) and Δ4(8)-iso-THC (trans-Δ-4,8-iso-tetrahydrocannabinol) have been identified as additional products of intramolecular cyclization. The use of Lewis and protic acids in different solvents has been studied to investigate the possible modulation of the reactivity of CBD (cannabidiol). The complete NMR spectroscopic characterizations of the four isomers are reported. High-performance liquid chromatography analysis and 1H NMR spectra of the reaction mixture were used to assess the percentage ratio of the compounds formed.
TL;DR: T tandem alkyl-arylations and phosphonyl- Darylations of vinyl ureas are reported by way of a photocatalytic radical-polar crossover mechanism and the conformationally accelerated Truce-Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring.
Abstract: We report tandem alkyl-arylations and phosphonyl-arylations of vinyl ureas by way of a photocatalytic radical-polar crossover mechanism. Addition of photoredox-generated radicals to the alkene forms a new C-C or C-P bond and generates a product radical adjacent to the urea function. Reductive termination of the photocatalytic cycle generates an anion that undergoes a polar Truce-Smiles rearrangement, forming a C-C bond. The reaction is successful with a range of α-fluorinated alkyl sodium sulfinate salts and diarylphosphine oxides as radical precursors, and the conformationally accelerated Truce-Smiles rearrangement is not restricted by the electronic nature of the migrating aromatic ring. Formally the reaction constitutes an α,β-difuctionalisation of a carbon-carbon double bond, and proceeds under mild conditions with visible light and a readily available organic photocatalyst. The products are α,α-diaryl alkylureas typically functionalized with F or P substituents that may be readily converted into α,α-diaryl alkylamines.
TL;DR: In this article, the authors simulate the microscopic dynamic process of the CO2 reduction process in the framework of density functional theory and demonstrate that desorption of CO from MoS2 edges is in virtue of unique diffusion process for adsorbed CO atoms.
TL;DR: It was found that gem-hydrogenation also provides opportunities for C–H functionalization, and silylated alkynes are shown to participate well in hydrogenative metathesis, which opens a new entry into valuable allylsilane building blocks.
Abstract: The only recently discovered gem-hydrogenation of internal alkynes is a fundamentally new transformation, in which both H atoms of dihydrogen are transferred to the same C atom of a triple bond while the other position transforms into a discrete metal carbene complex. [Cp*RuCl]4 is presently the catalyst of choice: the resulting piano-stool ruthenium carbenes can engage a tethered alkene into either cyclopropanation or metathesis, and a prototypical example of such a reactive intermediate with an olefin ligated to the ruthenium center has been isolated and characterized by X-ray diffraction. It is the substitution pattern of the olefin that determines whether metathesis or cyclopropanation takes place: a systematic survey using alkenes of largely different character in combination with a computational study of the mechanism at the local coupled cluster level of theory allowed the preparative results to be sorted and an intuitive model with predictive power to be proposed. This model links the course of the reaction to the polarization of the double bond as well as to the stability of the secondary carbene complex formed, if metathesis were to take place. The first application of "hydrogenative metathesis" to the total synthesis of sinularones E and F concurred with this interpretation and allowed the proposed structure of these marine natural products to be confirmed. During this synthesis, it was found that gem-hydrogenation also provides opportunities for C-H functionalization. Moreover, silylated alkynes are shown to participate well in hydrogenative metathesis, which opens a new entry into valuable allylsilane building blocks. Crystallographic evidence suggests that the polarized [Ru-Cl] bond of the catalyst interacts with the neighboring R3Si group. Since attractive interligand Cl/R3Si contacts had already previously been invoked to explain the outcome of various ruthenium-catalyzed reactions, including trans-hydrosilylation, the experimental confirmation provided herein has implications beyond the present case.
TL;DR: In this paper, a novel sustainable access to carboxamides was achieved via direct C-O bond cleavage of a range of esters using glycerol or 2-MeTHF as a solvent, in air.
Abstract: Lithium amides constitute one of the most commonly used classes of reagents in synthetic chemistry. However, despite having many applications, their use is handicapped by the requirement of low temperatures, in order to control their reactivity, as well as the need for dry organic solvents and protective inert atmosphere protocols to prevent their fast decomposition. Advancing the development of air- and moisture-compatible polar organometallic chemistry, the chemoselective and ultrafast amidation of esters mediated by lithium amides is reported. Establishing a novel sustainable access to carboxamides, this has been accomplished via direct C-O bond cleavage of a range of esters using glycerol or 2-MeTHF as a solvent, in air. High yields and good selectivity are observed while operating at ambient temperature, without the need for transition-metal mediation, and the protocol extends to transamidation processes. Pre-coordination of the organic substrate to the reactive lithium amide as a key step in the amidation processes has been assessed, enabling the structural elucidation of the coordination adduct [{Li(NPh2)(O[double bond, length as m-dash]CPh(NMe2))}2] (8) when toluene is employed as a solvent. No evidence for formation of a complex of this type has been found when using donor THF as a solvent. Structural and spectroscopic insights into the constitution of selected lithium amides in 2-MeTHF are provided that support the involvement of small kinetically activated aggregates that can react rapidly with the organic substrates, favouring the C-O bond cleavage/C-N bond formation processes over competing hydrolysis/degradation of the lithium amides by moisture or air.
TL;DR: The carbon–carbon double bond of unsaturated carbonyl compounds was readily reduced by using a phosphetane oxide catalyst in the presence of a simple organosilane as the terminal reductant and water as the hydrogen source.
Abstract: The carbon-carbon double bond of unsaturated carbonyl compounds was readily reduced by using a phosphetane oxide catalyst in the presence of a simple organosilane as the terminal reductant and water as the hydrogen source. Quantitative hydrogenation was observed when 1.0 mol % of a methyl-substituted phosphetane oxide was employed as the catalyst. The procedure is highly selective towards activated double bonds, tolerating a variety of functional groups that are usually prone to reduction. In total, 25 alkenes and two alkynes were hydrogenated to the corresponding alkanes in excellent yields of up to 99 %. Notably, less active poly(methylhydrosiloxane) could also be utilized as the terminal reductant. Mechanistic investigations revealed the phosphane as the catalyst resting state and a protonation/deprotonation sequence as the crucial step in the catalytic cycle.
TL;DR: An operationally simple and efficient one-pot protocol for the synthesis of highly functionalized thiazolidin-4-ones and thiazolines has been devised via Rh(OAc)2-catalyzed annulative coupling of β-ketothioamides with diazo compounds under mild conditions for the first time.
Abstract: An operationally simple and efficient one-pot protocol for the synthesis of highly functionalized thiazolidin-4-ones and thiazolines has been devised via Rh(OAc)2-catalyzed annulative coupling of β-ketothioamides with diazo compounds under mild reaction conditions for the first time. This double functionalization of diazo compounds proceeds via selective S-alkylation followed by intramolecular N-cyclization enabling the formation of C-S and C-N bonds at moderate temperature. Notably, the products possess Z-stereochemistry with regard to the exocyclic C═C double bond at the 2-position of the ring. Further, the synthetic utility of the strategy has been revealed to access 2,3-dihydrobenzo[d]thiazoles. Remarkably, atom economy and tolerance of a wide range of functional groups are added characteristics to this strategy.