Unconjugated Dienes Research Articles

Construction of remote cyano-substituted quaternary carbon centers via nickel-catalyzed migratory hydrocyanation of unconjugated dienes

Construction of remote cyano-substituted quaternary carbon centers via nickel-catalyzed migratory hydrocyanation of unconjugated dienes

Cover Picture

The cover picture shows polymer network trees grown from monomers’ grassland through photoinduced RAFT radical step‐growth polymerization between a series of unconjugated diene monomers and bifunctional xanthate. The obtained polymer network showed the ability of postfunctionalization through controlled way and degradation, which was benefitted from RAFT polymerization. More details are discussed in the article by Zhu et al. on page 503—508.image

Highly Enantioselective Nickel-Catalyzed Intramolecular Hydroalkenylation of N- and O-Tethered 1,6-Dienes To Form Six-Membered Heterocycles.

A highly enantioselective nickel-catalyzed intramolecular hydroalkenylation of N- or O-tethered 1,6-dienes was developed by using monodentate chiral spiro phosphoramidite ligands. The reaction provides an efficient and straightforward method for preparing very useful six-membered N- and O-heterocycles with high regioselectivity as well as excellent stereoselectivity from easily accessible starting materials under mild reaction conditions. The chiral spiro nickel catalyst developed in this study represents one of the few catalysts for highly enantioselective cyclization of unconjugated dienes.

Short-term peripheral sensitization by brief exposure to pheromone components in Spodoptera littoralis.

In insects, the olfactory system displays a high degree of plasticity. In Spodoptera littoralis, pre-exposure of males to the sex pheromone has been shown to increase the sensitivity of the olfactory sensory neurons at peripheral level. In this study, we have investigated this sensitization effect by recording the electroantennographic responses of male antennae to the major sex pheromone component (Z,E)-9,11-tetradecadienyl acetate and to the minor components (Z,E)-9,12-tetradecadienyl acetate and (Z)-9-tetradecenyl acetate. Responses to the conjugated diene acetate at 1 and 10µg and to the unconjugated ester at 10µg at three different times (11, 22 and 33min) after pre-exposure (T=0min) were significantly higher than those at T=0, whereas no increase of sensitivity to the pheromone was elicited by any dose of the minor monoene acetate. In addition, pre-exposed antennae to sub-threshold amounts (0.1, 1 and 10ng) of the major pheromone component also induced an increased response to the chemical at different times (5 and 15min) after exposure. Our results revealed that pre-exposed isolated antennae display a short-term higher sensitivity at the peripheral level when compared to naive antennae. In addition, we provide evidence of a peripheral sensitization mediated not only by the major pheromone component, but also by the minor unconjugated diene acetate, and the induction of this sensitivity appears to be dependent on the pre-exposure dose and the time span between pre-exposure and subsequent recordings. Possible implications of the sensitization effect displayed by the minor component for a more effective discrimination of the pheromone bouquets of other closely related species are highlighted.

Chirality Induced by the Interaction of C═C and C═X Bonds (X═CH2, NH, NH2+, O, and S) Separated by a Methylene Group.

The chirality derived from the interaction between two double bonds (C═C and C═X where X ═ CH2, NH, NH2+, O and S) across a methylene group has been examined in some detail at the B3LYP/aug-cc-pVTZ level. The rotamers of these formally achiral molecules that lead to large calculated specific rotations are those that allow overlap between the pair of double bonds, and the rotation is increased when the distance between them is decreased. Although the large specific rotation of unconjugated enones such as norbornenone is usually attributed to a magnetic transition dipole arising from an n-π* interaction of the carbonyl group, it has been found that large rotations may also be found with some conformations of unconjugated dienes such as 1,4-pentadiene. In the relative orientations of the double bonds that lead to large optical rotations, the pair of p-π orbitals are oriented so that they can interact leading to an electric transition dipole, while at the same time they are somewhat twisted with respect to each other allowing a significant magnetic transition dipole Other information was obtained by studying 2-propene-1-imine and its conjugate acid. The former gives only a small increase in optical rotation as compared to pentadiene. However, protonation at N leads to a large increase in optical rotation. This suggests that lone pairs have little effect on rotation, whereas the change in electronegativity has a large effect.

C-H Polyaddition of Dimethoxyarenes to Unconjugated Dienes by Rare Earth Catalysts.

The C-H polyaddition of dimethoxyarenes such as 1,4-dimethoxybenzene and 4,4'-dimethoxybiphenyl to unconjugated dienes such as norbornadiene and 1,4-divinylbenzene has been achieved for the first time by using cationic half-sandwich rare earth alkyl catalysts. This protocol afforded novel polymer materials consisting of dimethoxyarene moieties and nonpolar hydrocarbon structure motifs (cyclic, linear, and aromatic) in perfectly alternating sequences that are otherwise difficult to make. The reaction proceeded via C═C double bond insertion into a C-H bond ortho to each of the two methoxy groups in a step-growth polymerization fashion.

Reaction of cyclopropenes with a trichloromethyl radical: unprecedented ring-opening reaction of cyclopropanes with migration.

The direct addition reaction of chloroform to cyclopropenes under triethylborane-mediated radical reaction conditions to provide trichloromethylcyclopropanes has been developed. In contrast, using dimethylzinc as a radical initiator led to the formation of unconjugated esters via a domino sequence involving the addition of the trichloromethyl radical, rearrangement and ring-opening reactions.

Concise syntheses of insect pheromones using Z-selective cross metathesis.

Very short synthetic routes to nine cis-olefin-containing pheromones containing a variety of functionality, including an unconjugated (E,Z) diene, are reported. These lepidopteran pheromones are used extensively for pest control, and were easily prepared using ruthenium-based Z-selective cross metathesis, highlighting the advantages of this method over less efficient ways to form Z olefins.

Homo‐Diels–Alder reaction of a very inactive diene, bicyclo[2,2,1]hepta‐2,5‐diene, with the most active dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione. Solvent, temperature, and high pressure influence on the reaction rate

Solvent, temperature, and high pressure influence on the rate constant of homo‐Diels–Alder cycloaddition reactions of the very active hetero‐dienophile, 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (1), with the very inactive unconjugated diene, bicyclo[2,2,1]hepta‐2,5‐diene (2), and of 1 with some substituted anthracenes have been studied. The rate constants change amounts to about seven orders of magnitude: from 3.95.10−3 for reaction (1+2) to 12200 L mol−1 s−1 for reaction of 1 with 9,10‐dimethylanthracene (4e) in toluene solution at 298 K. A comparison of the reactivity (ln k2) and the heat of reactions (∆r‐nH) of maleic anhydride, tetracyanoethylene and of 1 with several dienes has been performed. The heat of reaction (1+2) is −218 ± 2 kJ mol−1, of 1 with 9,10‐dimethylanthracene −117.8 ± 0.7 kJ mol−1, and of 1 with 9,10‐dimethoxyanthracene −91.6 ±0.2 kJ mol−1. From these data, it follows that the exothermicity of reaction (1+2) is higher than that with 1,3‐butadiene. However, the heat of reaction of 9,10‐dimethylanthracene with 1 (−117.8 kJ mol−1) is nearly the same as that found for the reaction with the structural C=C counterpart, N‐phenylmaleimide (−117.0 kJ mol−1). Since the energy of the N=N bond is considerably lower (418 kJ/bond) than that of the C=C bond (611 kJ/bond), it was proposed that this difference in the bond energy can generate a lower barrier of activation in the Diels–Alder cycloaddition reaction with 1. Linear correlation (R = 0.94) of the solvent effect on the rate constants of reaction (1+2) and on the heat of solution of 1 has been observed. The ratio of the volume of activation (∆V≠) and the volume of reaction (∆Vr‐n) of the homo‐Diels–Alder reaction (1+2) is considered as “normal”: ∆V≠/∆Vr‐n = −25.1/−30.95 = 0.81. Copyright © 2012 John Wiley & Sons, Ltd.

ChemInform Abstract: Carbon-Carbon Bond Formation Using Manganese(III) Acetate as an Electrochemical Mediator.

Abstract Anodic oxidation in a solution containing a variety of olefins and a small amount of Mn(OAc)2·4H2O brought about Mn+3-mediated carbon—carbon bond formation, such as efficient carboxymethylation of styrene derivatives to the corresponding γ-aryl-γ-butyrolactones, and selective coupling of active methylene compounds with non-activated monoolefins, unconjugated dienes or 5-arylpent-1-enes.

ChemInform Abstract: Stereoselective Synthesis of Alcohols Containing (Z)- and (E)-Olefins, Dienes, Enynes and Styrenes: Cyclic β-Halogeno Ether Scissions Using Samarium Diiodide as the Electron-Transfer Agent.

In contrast to the sodium-mediated ring scission of 2-substituted 3-chloro ethers of the tetrahydrofuran series, samarium diiodide gives olefins of high (E)-stereoselectivity and provides (E)-conjugated and unconjugated dienes, styrenes and enynes in good yield without appreciable over-reduction. Whilst the SmI2 scission of 3-chloro-2-alkyltetrahydropyrans gives(Z)-rich (Z)/(E) olefin mixtures, the 2-(alk-1′-ynyl) members give (Z)-enyne alcohols with high stereoselectivity, providing a valuable complement to the (E)-enyne synthesis employing the tetrahydrofuran series.In electron-transfer scissions using sodium, the stereochemistry of the product alcohols is related to the ground-state conformation of the cis- and trans-pyrans and -furans. The slow SmI2-mediated reactions appear to involve samarium-complexed intermediates aving structures independent of the original conformation, or of the cis- or trans-geometry of the furan or pyran, and it is the transition states from these intermediates that determine the stereochemical outcome.Scissions in the tetrahydrofuran series can be accelerated by addition of HMPA or DMPU with only a little deterioration in stereoselectivity, but in the tetrahydropyran series there are drastic changes in product stereochemistry when DMPU is added. Brief comment is made on the synthesis of tetrahydro-furan and -pyran precursors.

Intramolecular Cycloaddition of Fluorinated 1,3,4‐Oxadiazoles to Dienes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Titanacyclobutenes or Titanium Vinyl Carbene Complexes? Reactivity of Organotitanium Species Generated by the Reaction of γ‐Chloroallyl Sulfides with a Titanocene(II) Reagent

The reactivity of the organotitanium species generated by the reductive titanation of gamma-chloroallyl sulfides with the titanocene(II) reagent [Cp(2)Ti{P(OEt)(3)}(2)] was studied. The organotitanium species formed from alpha-monosubstituted gamma-chloroallyl sulfides reacted with 1,5-diphenylpentan-3-one and styrene to produce conjugated dienes and vinyl cyclopropanes as major products, thus suggesting the formation of vinyl carbene complexes as intermediates. On the contrary, the organotitanium species generated from acyclic beta,gamma-disubstituted gamma-chloroallyl sulfides revealed titanacyclobutene-like reactivity, and their reaction with 1,5-diphenylpentan-3-one produced homoallyl alcohols. These organotitanium species did not react with styrene, but did react with dichlorophenylphosphine to afford phosphacyclobutenes. In the case of beta-monosubstituted, gamma-monosubstituted, and alpha,gamma-disubstituted gamma-chloroallyl sulfides, the organotitanium species reacted with both 1,5-diphenylpentan-3-one and styrene. The former reaction produced homoallyl alcohols and the latter gave vinyl cyclopropanes or unconjugated dienes. These results suggest that titanacyclobutenes and/or titanium vinyl carbene complexes are produced by the reductive titanation of gamma-chloroallyl sulfides depending on their substitution patterns.

Intramolecular cycloaddition of fluorinated 1,3,4-oxadiazoles to dienes

Cycloaddition reactions of fluorinated 1,3,4-oxadiazoles with conjugated and unconjugated dienes was studied. The reactions resulted in the formation of products of double cycloaddition (7-oxabicycloheptane type compounds), along with products of intramolecular cycloaddition (oxatricyclic and oxatetracyclic compounds). The structure of 4-(trifluoromethyl)-2-ethoxycarbonyl-1,6-dimethyl-3-oxatricyclo[2.2.1.0 2,6]heptane was confirmed by single crystal X-ray diffraction analysis.

Cyclopolymerization, 30. Design of an Unconjugated Diene with High Polymerizability Using Functional Groups with No Homopolymerization Tendency, and Synthesis of Completely Cyclized Polymers therefrom: Radical Polymerizations of N-Phenyl-N-2-(methoxycarbonyl)allyl(meth)acrylamide

Cyclopolymerizabilities of N-phenyl-N-2-(methoxycarbonyl)allylmethacrylamide (1 a) and N-phenyl-N-–2-(methoxycarbonyl)allylacrylamide (1 b) were compared to see the validity of the concept proposed previously for the design of 1,6-dienes with both a high cyclization tendency and a high polymerizability. It states that the use of functional groups with a higher conjugative nature together with a no homopolymerization tendency is essential for the purpose. Of the four monofunctional counterparts of these dienes, only N-phenyl-N-2-(methoxycarbonyl)propylacrylamide, one of the monoene counterparts of 1 b, is assumed to have high homopolymerization tendency, judging from the polymerizabilities of compounds with similar structure. α-Substituted acryloyl groups of 1 a and 1 b have higher conjugative natures. This indicates that both the dienes have high polymerizability but their cyclization tendency is essentially different; i. e., 1 a yields highly cyclized polymers, while polymers with lower degrees of cyclization are obtained from 1 b. The results obtained were in good accordance with this consideration. Repeat cyclic units of poly(1 a) and poly(1 b) consist mainly of five-membered rings. Both the double bonds of 1 b were pendant unsaturations in poly(1 b). Mechanism of the polymerizations was discussed based on the results obtained.

Cyclopolymerization XXVIII. Radical Polymerizations of N-Substituted N-Methallyl-2-(methoxycarbonyl)allylamines: Polymerizability of Unconjugated Dienes with Functional Groups with Low Homopolymerization Tendency

Radical cyclopolymerizations of N-substituted-N-methallyl-2-(methoxycarbonyl) allylamines (1) were studied to compare their cyclopolymerizabilities with those of N-substituted-N-allyl-2-(methoxycarbonyl) allylamines (2). Monomers 1 with a phenyl(1a) and a t-butyl(1b) group as an N-substituent were employed. The phenyl group was chosen, since 2 with an N-phenyl group(2a) was reported to have exceptionally low polymerization tendency among 2. Monomer 1b was polymerized to see whether the bulky N-t-butyl group enhances the cyclization tendency of 1 or not, since 1 with an N-methyl group(1c) was reported to yield polymers with pendant unsaturations, though their content is low. It was found that polymerizations of 1a proceed very slowly like 2a, but the reason for their slow polymerizations was left unsolved. Polymers with high degree of cyclization, 96% for poly(1a) and 100% for poly(1b), were obtained even in their bulk polymerizations. This could be an additional support for the proposal made previously. It states that unconjugated dienes, for which monofunctional counterparts do not have homopolymerization tendency yield highly cyclized polymers. This is because both the monofunctional counterparts of 1 are considered to have essentially no homopolymerization tendency. The bulky t-butyl group was found to be effective to enhance cyclization tendency also in 1. Structural studies showed that poly(1a) and poly(1b) contain both six- and five-membered rings as repeat cyclic units. Mechanism for intramolecular cyclization was discussed.

Cyclopolymerization. Part XXVII. Cyclopolymerizability of an unconjugated diene with functional groups with no homopolymerization tendency: radical polymerization of N-methyl- N-methallyl-2-(methoxycarbonyl)allylamine and structure of the polymers derived therefrom

Radical cyclopolymerizations of N-methyl- N-methallyl-2-(methoxycarbonyl)allylamine ( 1) were studied to see the validity of the proposal made previously. It states that the use of functional groups with a higher conjugative nature together with no homopolymerization tendency is essential for the design of 1,6-dienes with not only a high cyclization tendency but also high polymerizability. Monomer 1 was designed, since non-homopolymerizability of both the monofunctional counterparts of 1 could be assumed reasonably based on the reported polymerization behavior of compounds with similar structures. The α-substituted acryloyl group of 1 was found to have high conjugative nature and polymerizations of 1 proceeded rapidly to yield polymers with degree of cyclization of 97% even in its bulk polymerizations. The results thus obtained were fundamentally in accordance with what had been expected from the proposal. Structural studies showed that poly( 1) consists almost exclusively of six-membered rings as repeat cyclic units. Mechanism for intramolecular cyclization during the cyclopolymerization of 1 was discussed based on the structural characteristics of poly( 1) along with those reported for the polymers obtained from diallyl monomers.

Theoretical spectroscopy of organic systems

The complete active space (CAS) SCF method in conjunction with the multiconfigurational second-order perturbation theory (CASPT2) has been applied to study the electronically excited states of basic organic compounds. As shown in the lecture with a number of examples, the CASPT2 method is capable of yielding accurate results for relative energies and other properties of excited states, provided that flexible one-electron basis sets are employed. The applications comprise an ample range of systems and problems, including polyenes, conjugated and unconjugated dienes, alternant and nonalternant hydrocarbons, polyenals, etc. As a whole these studies enable both qualitative and quantitative understanding of electronic spectra of organic molecules of fundamental importance.

Orientational and Stereochemical Preferences in [Hydridotris(3,5-dimethyl-1-pyrazolyl)borato](CO)2W(η3-allyl) Complexes

Irradiation of Tp‘(CO)3WH in the presence of alkynes or unconjugated dienes generates η3-allyl complexes, Tp‘(CO)2W(η3-CHRCHCHR‘). A kinetic preference for anti-alkyl substitution due to η2-vinyl intermediates exists for the reactions with terminal alkyne substrates. The monoalkyl-substituted allyl complexes are configurationally stable on the NMR time scale but show a thermodynamic preference for syn-substitution upon heating in solution. Separate crystal structures of the syn and anti isomers of the 1-methylallyl complex, Tp‘(CO)2W(η3-CH2CHCHCH3), have revealed isomers which differ by approximately 90° in allyl orientation (θ). The term meso is introduced to emphasize the orthogonal relationship between the anti (θ = 30°, exo) and the syn (θ = 120°, meso) isomers. The change in orientation of the allyl is accompanied by a change in the OC−W−CO angle from acute to obtuse in order to maximize donation from the π-nonbonding orbital of the allyl into the dπ metal orbitals. EHMO (extended Huckel molecular or...

Reaction of Unconjugated Dienes with [Fe(R2P(CH2)nPR2)] Species

The effect of varying the bidentate ligand upon the reaction of unconjugated dienes with (R2P(CH2)nPR2)Fe0 species has been investigated. Depending upon the nature of the substituents at phosphorus and upon the length of the hydrocarbon chain joining the phosphorus atoms, either (η2:η2-diene)Fe(R2P(CH2)nPR2) or (η5-dienyl)Fe(R2P(CH2)nPR2)H species are formed. Extended Huckel MO-calculations have been used to assess the importance of electronic factors in influencing the course of reaction, and it can be shown that distortion of the tetrahedral geometry of the (diene)Fe species causes a destabilization.