Vinylation Reaction Research Articles

Synthesis of the C38–C54 spiroketal segment of halichondrin B

Stereoselective synthesis of the C38–C54 segment of a marine metabolite halichondrin B comprising KLM and N rings with a C44 spiroketal including 10 chiral centers is described. The salient features of the synthesis are Carreira’s addition, Sharpless asymmetric dihydroxylation and double alkylation of TosMIC strategy and double vinyl coupling reactions.

Synthesis and Singlet Oxygen Reactivity of 1,2‐Diaryloxyethenes and Selected Sulfur and Nitrogen Analogs

1,2-Diaryloxyethene has recently been proposed as a linker in singlet oxygen-mediated drug release. Even though 1,2-diaryloxyethenes look very simple, their synthesis was not an easy task. Previous methods are limited to symmetric molecules, lengthy step and low yield. We report on a facile synthetic method not only for 1,2-diaryloxyethenes but also their sulfur and nitrogen analogs in yields ranging from 40 to 90% with more than 90% purity at the vinylation reaction.

N-Heterocyclic carbene-catalyzed cascade annulation reaction of o-vinylarylaldehydes with nitrosoarenes: one-step assembly of functionalized 2,3-benzoxazin-4-ones

The NHC-catalyzed reactions of ortho electron-deficient vinyl substituted arylaldehydes with nitrosoarenes were studied. The reactions produced multifunctional 2,3-benzoxazin-4-ones in good to excellent yields via a cascade aza-benzoin reaction between aldehyde and nitroso groups followed by an intramolecular oxo-Michael addition. The resulting 1-acetate substituted 2,3-benzoxazinones were transformed into a new type of β-hydroxycarboxylate derivatives or 3-oxo-1-isobenzofuranacetates, respectively, under different reductive conditions. This work not only provides a simple and efficient method for the construction of multifunctional 2,3-benzoxazin-4-ones of potential pharmacological interest, but also expands the application of NHC-catalyzed cascade reactions in the formation of carbon-heteroatom and heteroatom-heteroatom bonds.

Fe3O4@mesoporous SBA-15: a robust and magnetically recoverable catalyst for one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones via the Biginelli reaction

A magnetic nanoparticle conjugated mesoporous nanocatalyst (Fe(3)O(4)@mesoporous SBA-15) with a high surface area has been synthesized by chemical conjugation of magnetite (Fe(3)O(4)) nanoparticles with functionalized mesoporous SBA-15. Functionalized mesoporous SBA-15 containing surface carboxyl and amino groups was synthesized via the thiol-ene click reaction of cysteine hydrochloride and vinyl functionalized SBA-15. The catalytic activity of the robust, safe and magnetically recoverable Fe(3)O(4)@mesoporous SBA-15 nanocatalyst was evaluated in the Biginelli reaction under mild conditions for the synthesis of a diverse range of 3,4-dihydropyrimidin-2(1H)-ones. The separation and reuse of the Fe(3)O(4)@mesoporous SBA-15 nanocatalyst were simple, effective and economical.

Validation and analysis of detailed kinetic models for ethylene combustion

Present work aims at evaluation of contemporary comprehensive detailed kinetic mechanisms for ethylene combustion, including the Konnov mechanism, LLNL nButane mechanism, San Diego (UCSD) mechanism and USC mechanism. These models have been validated by extensive comparison with available experimental data on ethylene ignition and flame propagation. The experimental data from the literature have been carefully examined to accurately assess the models’ predicting performance. Noticeable differences in the predictions of ethylene ignition and flame propagation under a variety of conditions have been observed. Moreover, sensitivity analysis has been conducted to identify important reactions for the prediction of ethylene ignition and flames. For ethylene ignition, it was found that C2H4 consumption reactions with radicals OH, O and subsequent reactions of vinyl with oxygen have dominant effect on predicted ignition delays. The pathway analysis has also been performed for each mechanism to identify different reaction pathways in ethylene ignition process. For ethylene flames, sensitivity analysis shows that H–O and C1 chemistry reactions significantly influence the laminar burning velocity in lean ethylene/air flames, while C2 chemistry reactions become of increasing importance in fuel-rich flames. Furthermore, to better understand the models’ predicting behavior, the differences in the reaction rate constants and routes of C2H4 and vinyl chemistry have been analyzed and discussed.

Synthetic Exploitation of Halogenated Alkenes Containing EWG: Polysubstituted Sulfanyl Dinitro Butadienes from Sequential Nucleophilic Substitutions

Our novel approach starts from a 1,1,3,4-tetrachloro-2,4-dinitrobuta-1,3-diene (5) being one of the most prominent members of this relatively new class of synthetic building blocks. Because of its multifunctional chemical behavior, polyhalogenated nitrobuta-1,3- dienes proved to be versatile reagents in the synthesis of a large variety of sulfurated, (hetero)cyclic, and acyclic derivatives. We describe our studies concerning successive nucleophilic vinylic substitution reactions of dinitrobuta-1,3-diene in order to establish the reactivity profile of this precursor and determine whether this precursor could be used for the synthesis of many dinitrodiene analogues offering new methodology for the synthesis of polyfunctional precursors that are difficult to access. Some of the resulting perfunctionalized 2,4- dinitrobuta-1,3-dienes are subjected to further transformations to give promising candidates with respect to biological activity. Keywords: Click chemistry, Dienes, Nitro compounds, Nitroalkenes, Persulfurated Alkenes, Polyhalogenated Compounds, Polysulfanyl Buta-1,3-dienes, Sulfides

Allylsilanes in “Tin‐free” Oximation, Alkenylation, and Allylation of Alkyl Halides

Tin-free oximation, vinylation, and allylation of alkyl halides have been developed by using allylsilanes as di-tin surrogates. Initiation of the radical process with a peroxide provides the silyl radical, which can abstract a halogen from the corresponding alkyl halide. The resulting carbon-centered radical then adds to various acceptors, including a sulfonyloxime, a vinylsulfone, and an allylsulfone, leading to formation of the desired products along with the corresponding allylsulfone resulting from the reaction of the PhSO(2) radical with the allylsilane precursor. Better results were generally obtained with methallylsilane 1b than with 1a. This observation was rationalized by invoking the higher nucleophilicity of 1b and the faster β-fragmentation of the corresponding β-silyl radical intermediate. Calculation of the energy barrier for the β-fragmentation of a series of β-silyl radicals at the DFT level supported this hypothesis. Finally, a second version of these oximation and vinylation reactions, based on the utilization of 3-tris(trimethylsilyl)silylthiopropene, was devised, affording the desired oximes and olefins in reasonable yields. This strategy allowed the title reaction to be performed under milder conditions (AIBN, benzene, 80 °C), as a result of the easier β-fragmentation of the C-S bond as compared with the C-Si bond.

Iridium-Catalyzed Allylic Vinylation and Asymmetric Allylic Amination Reactions with o-Aminostyrenes

An Ir-catalyzed allylic vinylation reaction of allyl carbonates with o-aminostyrene derivatives has been realized, providing skipped (Z,E)-diene derivatives. With (E)-but-2-ene-1,4-diyl dimethyl dicarbonate as the substrate, an efficient enantioselective synthesis of 1-benzazepine derivatives via an Ir-catalyzed domino allylic vinylation/intramolecular allylic amination reaction has been developed. Mechanistic studies of the allylic vinylation reaction have been carried out, and the results suggest that the leaving group of the allylic precursor plays a key role in directing the reaction pathway. Screening of various allylic precursors showed that Ir-catalyzed reactions of allyl diethyl phosphates with o-aminostyrene derivatives proceed via an allylic amination pathway. A subsequent ring-closing metathesis (RCM) reaction of the amination products led to a series of enantiomerically enriched 1,2-dihydroquinoline derivatives. Their utility is indicated by an asymmetric total synthesis of (-)-angustureine.

Concise One-step Synthesis of 4-Arylidene-1,3-oxazolidin-2-ones with Internal Propargylic Alcohols and Isocyanates

Oxazolidinones and their derivatives are widely used, as chiral synthons or chiral auxiliaries and as bioactive scaffolds in numerous natural products. Due to the importance of their structures, several methods for the synthesis of 1,3oxazolidin-2-ones have been reported. Classical methods for formation of these heterocyclic rings involve condensation reactions between corresponding amino alcohols and carbonyl precursors such as phosgene, chloroformate and dialkyl carbonates. An alternative approach is the cyclization reaction of vinyl or propargyl carbamate catalyzed by base or transition metal catalyst, in which a variety of substituted oxazolidinones are obtained under milder conditions. Tamaru, Gagosz, and Schmalz reported the synthesis of 4-alkylidene1,3-oxazolidin-2-one from O-propargyl carbamates using Cu(I) and Au(I) catalyst, whereas Chandrasekaran reported LiOH-catalyzed reaction method with DMF solvent. However, these procedures were mostly applied to the construction of 4-methylene-1,3-oxazolidin-2-one, and only a few 4-substituted methylene ones have been reported. Another method using CO2 as a carbonyl source has also been developed, 5

Highly Regioselective Synthesis of 3′-O-Acyl-Trifluridines Catalyzed by Pseudomonas cepacia Lipase

3'-O-Acyl-trifluridines were prepared successfully through an enzymatic approach for the first time. Among the ten commercially available lipases tested, Pseudomonas cepacia lipase displayed the highest regioselectivity towards the acylation of 3'-hydroxyl of trifluridine. Furthermore, the effects of some crucial factors on the enzymatic myristoylation of trifluridine were examined. The optimal reaction medium, molar ratio of trifluridine to vinyl myristate and reaction temperature were found to be anhydrous THF, 1:7 and 50 °C, under which the reaction rate, substrate conversion, and 3'-regioselectivity were 63.9 mM/h, >99.0%, and 99%, respectively. Additionally, the enzyme recognition of the chain length of the acyl donors was investigated. The results showed that 3'-regioselectivity of the enzyme maintained 99% with the increment of acyl chain length (C6, C10, and C14). The reason might derive from the strong hydrophobic interaction between 5-CF(3) group of the base moiety and Leu 287 located in the medium-sized pocket of the active site.

Halogenophilic and classical Ad N E mechanisms in nucleophilic vinylic substitution reactions involving the anions of transition metal carbonyls

The mechanism of the reaction of carbonylate anions ([M(CO) n L]–) with highly activated vinyl halides (Hal = Cl, Br, I) was investigated by the method of “anion traps” – the effect of proton donors on the composition of the reaction products. It was demonstrated that the reactions with PhCHal=C(Z)2 (Hal = Br, I;Z=CN, CO2Et) and PhCN=CClI take place through initial attack by the carbonylate at the halogen atom, the reactions with PhCCl=C(CO2Et)2 and PhCOCH=CHHal (Hal = Cl, I) take place through attack by the carbonylate at the π bond (AdNE mechanism), and in the case of E-and Z-PhCN=CHI the two mechanisms operate concurrently. The main laws determining the reaction mechanisms are analyzed.

Functionalization of Single-Walled Carbon Nanotubes with Poly(methyl methacrylate) by Emulsion Polymerization

Covalent grafting of acrylate-functionalized single-walled carbon nanotubes (SWCNTs) with poly(methyl methacrylate) was accomplished by emulsion polymerization using sodium dodecylbenzene sulfonate (SDBS) as an emulsifying agent. The acrylate-functionalized SWCNTs with polymerizable vinyl groups on their surfaces were prepared by a reaction sequence involving oxidation, hydroxylation, and vinylation reactions. The as-prepared acrylate-functionalized SWCNTs were then dispersed in water in the presence of SDBS, resulting in the exfoliation of SWCNTs into small bundles of approximately 2−6 tubes and the simultaneous formation of SWCNT micelles. Subsequent addition of methyl methacrylate resulted in its absorption into the SWCNT micelles due to the interactions between the monomer and the nanotube surface. Grafting copolymerization of methyl methacrylate with the vinyl groups on the SWCNT surface was subsequently performed in the micelles to produce poly(methyl methacrylate)-functionalized SWCNTs. Thermogravimetric analysis indicated that the average polymer content in the functionalized SWCNTs ranged from 42 to 63 wt %, depending on the time of monomer pre-emulsion.

Transition-Metal-Catalyzed Regioselective Arylation and Vinylation of Carboxylic Acids

Arene and heteroarene carboxylic acids undergo regioselectivearylation and vinylation reactions at the positions ORTHO ( CINE)and IPSO to their carboxyl function undertransition-metal catalysis; these reactions are accompanied by carbon-hydrogenand carbon-carbon bond cleavages, respectively. Recentprogress in this area is summarized in this article. 1 Introduction 2 ORTHO- ( CINE-)Arylation 3 ORTHO- ( CINE-)Vinylation 4 IPSO-Arylation 5 IPSO-Vinylation 6 Conclusions

ChemInform Abstract: Chemical Reactions Induced and Probed by Positive Muons

The application of μ+ science, collectively called μSR, but encompassing a variety of methods including muon spin rotation, muon spin relaxation, muon spin repolarization, muon spin resonance and level-crossing resonance, to chemistry is introduced emphasizing the special aspects of processes which are “induced and probed” by the μ+ itself. After giving a general introduction to the nature and methods of muon science and a short history of muon chemistry, selected topics are given. One concerns the usefulness of muonium as hydrogen-like probes of chemical reactions taking polymerization of vinyl monomers and reaction with thiosulphate as examples. Probing solitons in polyacetylene induced and probed by μ+ is also an important example which shows the unique nature of muonium. Another important topic is “lost polarization”. Although this term is particular to muon chemistry, the chemistry underlining the phenomenon of lost polarization has an importance to both radiation and hot atom chemistries.

ChemInform Abstract: Photochemical Reactions of Vinyl-, Styryl-, and Benzyl-Substituted Digermanes.

Photochemical reactions of vinyl-, styryl-, and benzyl-substituted digermanes were investigated by chemical trapping experiments. Photolysis of vinylpentamethyldigermane afforded 1-trimethyl-2-(pentamethyldigermyl)ethane as a major product, and styrylpentamethyldigermanes gave mainly styryltrimethylgermane. On the other hand, photolysis of benzyl-substituted digermanes (benzylpentamethyldigermane and 1,2-dibenzyltetramethyldigermane) gave hydrogermanes and hydrodigermanes as main products, respectively. These products were derived from germyl radicals generated by photoinduced homolysis of the germanium–germanium bond. In carbon tetrachloride (CCl4), these germyl radicals were converted to the corresponding chlorogermanes by abstraction of a chlorine atom. Germylene species were also to be evolved from such photolyses.

ChemInform Abstract: An Efficient Palladium-Catalyzed Reaction of Vinyl and Aryl Halides or Triflates with Terminal Alkynes.

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ChemInform Abstract: Ni(0)-Catalyzed Reactions of Aryl and Vinyl Halides with Alkenes and Alkynes.

Ni(P(OPh)3)4 and Ni(P(OEt)3)4 catalyze tile reaction of aryl and vinyl halides with olefins (l-leck reaction) and alkynes. © 1997 Elsevier Science Ltd. The formation of C-C bonds by the reaction of aryl halides with olefins (Heck reaction) in presence of palladium catalysts is a well studied reaction) We have been investigating the use of other metal catalysts for this reaction based on the known mechanism of the Pd catalyzed vinylation reaction. The key step in the reaction mechanism is the oxidative addition of a low valent coordinatively unsaturated metal complex to the aryl halide followed by olefin coordination, migratory insertion and reductive elimination. We have reported the use of Co(1), Rh (I) (Wilkinson's Catalyst) and Ir(1) (Vaska's complex) successfully based on this rationale, 2 We decided to investigate other new catalysts for the Heck reaction based on the reaction mechanism viz. a metal complex capable of oxidative addition reductive elimination and undergoing ligand dissociation and association. NiCI2(PPh3)2 is known to catalyze the reaction of aryl and aliphatic halides with olefins in the presence of Zn dust to give mixtures of addition and substitution products) But it is not a very useful catalyst for the Heck reaction because it gives different types of products with ethylacrylate (addition product) and styrene (substitution product). The highly active and air sensitive complex, Ni(PPh3)4, generated in situ by the action of Et3AI on Ni(acac)2, has been used for the intramolecular reaction of aryl halides with olefins to form indoles: Ni(P(OPh)3)4 and Ni(P(OEt)3)4 are stable metal complexes of Ni(0) and are well known to undergo ligand dissociation, oxidative addition and reductive elimination reactions and have been used to catalyze the reaction of allyl acetates with nucleophiles, s We report here, the first use of these stable Ni(0) metal complexes, for the activation of aryl halides for reaction with olefins (Heck reaction) and alkynes.

An ab initio quantum chemical study of reaction mechanisms in the C2H2/CH3OH/KOH/DMSO system

An ab initio quantum chemical study (MP2/6-311++G**//B3LYP/6-31+G*) of a number of possible interactions is performed for the gas phase system of acetylene—potassium hydroxide-dimethylsulfoxide(DMSO)—methanol and with regard to the solvent effect within the continuum model. Key structures in the vinylation reaction are shown to be methoxide ion complexes with the alkali metal hydroxide and acetylene molecules. The formation of these complexes results in the activation of the acetylene molecule and an increase in the nucleophilicity of the methoxide ion. In the C2H2/CH3OH/KOH/DMSO reaction system, a proton exchange between the acetylene molecule and the anionic nucleophile ([OH]- and [CH3O]-) is freely performed with the formation of systems with ethynideions, whereas the thermodynamically preferable formation of vinyl alcohol or methyl vinyl ether is determined by a barrier of 20 kcal/mol.

Effects of stereochemistry and β-substituents on the rates of vinylic S N2 reaction of hypervalent vinyl(phenyl)-λ 3-iodanes with tetrabutylammonium halides

Both stereoisomers of β-(2-phenylethoxy)vinyl-λ 3-iodane and ( Z)-β-aroyloxyvinyl-λ 3-iodane were prepared stereoselectively. These substituted vinyl-λ 3-iodanes undergo nucleophilic vinylic substitutions with n-Bu 4NX (X=Cl, Br, I) under mild conditions, yielding vinyl halides. The observed inversion of configuration at the ipso vinylic carbon atom is compatible with a concerted vinylic S N2 mechanism. Kinetic measurements indicated that the rates for vinylic S N2 reaction of ( Z)-vinyl-λ 3-iodane are greater than those of the E-isomer, probably because of the higher ground state energy of the Z-isomer. Electronic effects of β-substituents of vinyl-λ 3-iodanes in the vinylic S N2 reaction are also discussed.

Pd‐Promoted Homocoupling Reactions of Unsaturated Silanes in Aqueous Micelles

AbstractPalladium‐promoted homocoupling reaction of vinyl‐ andpolyenylsilanes in aqueous conditions has been investigated. The reaction is catalyzed by PdCl2 in the presence of the reoxidizing system CuCl2/LiCl and occurs at room temperature in aqueous solutions containing nonionic amphiphiles. Symmetrically α,ω‐disubstituted stereodefined all‐trans polyenes have been obtained in mild conditions and in good yields (65–87 %), higher than those previously reported for the same reactions carried out in methanol or HMPA. A comparison between two commercially available surfactants, Triton X‐100 and PTS, has been performed.