Cyclic Double Bond Research Articles

Manipulation of the cyanido-bridged Fe2W2 rhombus in the crystalline state: Co-crystallization, desolvation and thermal treatment

We present the new cyanido-bridged rhombus {[FeII(TPMA)]2[WV(CN)8]2}2– (Fe2W2) (TPMA = tris(2-pyridylmethyl)amine) cluster as a potential Secondary Building Block (SBB) for construction of polynuclear molecular materials. Fe2W2 is formed easily in self-assembly process between [FeII(TPMA)]Cl2 and TBA3[W(CN)8] in H2O/MeOH media, and was co-crystallized in (TBA)2{Fe2W2}⋅2H2O (1), and (TBA)2{Fe2W2}⋅mMeOH⋅nH2O (2) solvated salts, and in (TBA)2{Fe2W2}⋅H3PG⋅mMeOH⋅nH2O (3) (H3PG = phloroglucinol, 1,3,5-trihydroxybenzene; co-former) solvated co-crystal salt. Crystals of 1 undergo reversible SCSC transformation 1 ⇄ 1deh upon controlled dehydration and rehydration processes, whereas crystals of 2 reveal anisotropic thermal expansion during heating from 100 K to room temperature. Both processes involve changes of the selected intermolecular distances or local molecular reorientation involving intermolecular cation–anion and anion-anion contacts. [FeII(TPMA)(µ-NC)2] moieties reveal low-spin (LS) state in each case, however, conformation of the Fe2W2 rings varies from the “staggered” in 1, nearly “eclipsed” in 2 to fully “eclipsed” in 3, which is attributed to various hydrogen bond CNN⋅⋅⋅HO schemes involving the terminal cyanido ligands in [W(CN)8]3– and co-crystallizing molecules. In particular, the conformation of Fe2W2 in 3 is fully controlled by an unprecedented cyclic double hydrogen bond {Fe2W2}⋅⋅⋅H3PG synthon, H3PG forming a bridge over the Fe2W2 rhombus plane through binding the opposite [W(CN)8] corners. This arrangement is co-stabilized by close-to-parallel contacts of H3PG with TPMA walls protruding out of the rhombus plane. The Fe2W2 rhombus is stable in MeOH solution and shows notable affinity to H3PG in the gas phase, which was confirmed by ESI-MS data. UV–Vis-NIR spectroscopy discloses an optical FeII → WV MMCT transition and mixed-valence FeII//III-WV/IV electronic ground state.

The quantum chemical study of the mechanism of the epoxidation reaction of limonene and geraniol with peracetic and perbenzoic acids

Aim. To compare the mechanism of the epoxidation reaction of terpenes Geraniol and Limonene with peracetic acid and perbenzoic acid based on the quantum chemical study. Materials and methods . For the calculation the density functional theory (approximation UBH & HLYP/6-31G (d) Gaussian 09) method was applied. The specified density functional allows to correctly describing biradical structures; it is rather economic in terms of the computer time cost, which allows its use in the study of sufficiently complex organic compounds and reactions. Results and discussion . The quantum chemical study of mechanisms of the epoxidation reaction of such terpenes as Geraniol and Limonene with peracetic and perbenzonic acids using the density functional theory (approximation UBH & HLYP/6-31G (d) Gaussian 09 program) has been conducted. It has been shown that epoxidation of geraniol with both peroxyacids occurs preferably by the double bond C 6 =C 7 due to stabilization of the corresponding transition state as a result of formation of hydrogen bond between the allyl hydroxyl group and the oxygen atom of the peroxy acid. Epoxidation of Limonene with perbenzoic and peracetic acids occurs via the cyclic double bond characterized by the lowest activation barrier, and it is consistent with the regioselectivity of the process generally known and experimentally proven. Conclusions . The results obtained are consistent with the experimental data, confirming the correctness of the use of this UBH & HLYP/6-31G (d) approach to study the regiochemical pecularities of the epoxidation process of alkenes containing several isolated double bonds.

One pot, three component 1,3 dipolar cycloaddition: Regio and diastereoselective synthesis of spiropyrrolidinyl indenoquinoxaline derivatives

A competent and highly discriminating one-pot synthesis of highly diversified novel functionalized indenoquinoxalone grafted spiropyrrolidine linked chromene-3-carbonitrile conjugates accumulating three pharmocophoric cores, heterocyclic indenoquinoxalone, pyrrolidines and chromene-3-carbonitrile in a single molecular framework by means of 1,3-dipolar cycloaddition reaction between indenoquinoxalone, proline/benzyl amine and chromene-3-carbonitrile in ethanol under classical and microwave conditions is described. The three component 1,3-dipolar cycloaddition reaction proceeds via in situ generation of azomethine ylides by the decarboxylative condensation of indenoquinoxalone with proline/benzyl amine and their selectivity towards the endo cyclic double bonds of dipolarophile (chromene-3-carbonitrile) leading to the formation of highly functionalised regio- and diastereoselective molecular hybrids. This methodology exemplifies the green chemistry protocol such as mild reaction conditions, high yields, one-pot procedure and operational simplicity.

A general mixture equation of state for double bonding carboxylic acids with ≥2 association sites.

In this paper, we obtain the first general multi-component solution to Wertheim's thermodynamic perturbation theory for the case that molecules can participate in cyclic double bonds. In contrast to previous authors, we do not restrict double bonding molecules to a 2-site association scheme. Each molecule in a multi-component mixture can have an arbitrary number of donor and acceptor association sites. The one restriction on the theory is that molecules can have at most one pair of double bonding sites. We also incorporate the effect of hydrogen bond cooperativity in cyclic double bonds. We then apply this new association theory to 2-site and 3-site models for carboxylic acids within the polar perturbed chain statistical associating fluid theory equation of state. We demonstrate the accuracy of the approach by comparison to both pure and multi-component phase equilibria data. It is demonstrated that the 3-site association model gives substantially a different hydrogen bonding structure than a 2-site approach. We also demonstrate that inclusion of hydrogen bond cooperativity has a substantial effect on a liquid phase hydrogen bonding structure.

Highly regioselective homoallyl alcohol protection through ring opening of p-methoxybenzylidene acetal

A highly regioselective homoallylic alcohol protection was achieved in the reductive cleavage of anisylidene acetal with DIBAL-H during the selective protection of hydroxyl group in terminal unsaturated diols which was unlikely compare to the diols present adjacent to internal and cyclic double bond. Reductive cleavage of terminal olefenic diols protected as its acetals gave exclusively allyl alcohol product in good to excellent yield. Though the actual reason of such observation is not quite clear, the current reductive protocol can be applied as an efficient solution for indirect protection of less reactive hydroxy group in preference to that of more reactive allylic one as PMB-mono ether.

ChemInform Abstract: Nazarov Cyclization of Divinyl Ketones Bearing an Ester Group at the β‐Position: A Remarkable Effect of α‐Substitution and Alkene Geometry on Regioselectivity.

The Nazarov cyclization of divinyl ketones with an ester at the β-position was examined with particular reference to where the cyclic double bond forms. We observed unprecedented regioselectivity, dictated by the subtle substitution patterns at the α-position and alkene geometry of α,β and mostly, this selectivity is regardless of substitutions at α′- and β′-positions. The major implications of these observations are an aromatic group at the α-position with E-olefin geometry provides a cyclopentenone in which the double bond is not in conjugation with an ester, whereas Z-olefin provides a cyclopentenone in which the double bond is in conjugation with an ester; and divinyl ketones bearing an ester group at the β-position and an alkyl group at the α-position with E-olefin geometry provide a cyclopentenone in which the double bond is in conjugation with the ester.

Nazarov cyclization of divinyl ketones bearing an ester group at the β-position: a remarkable effect of α-substitution and alkene geometry on regioselectivity.

The Nazarov cyclization of divinyl ketones with an ester at the β-position was examined with particular reference to where the cyclic double bond forms. We observed unprecedented regioselectivity, dictated by the subtle substitution patterns at the α-position and alkene geometry of α,β and mostly, this selectivity is regardless of substitutions at α'- and β'-positions. The major implications of these observations are an aromatic group at the α-position with E-olefin geometry provides a cyclopentenone in which the double bond is not in conjugation with an ester, whereas Z-olefin provides a cyclopentenone in which the double bond is in conjugation with an ester; and divinyl ketones bearing an ester group at the β-position and an alkyl group at the α-position with E-olefin geometry provide a cyclopentenone in which the double bond is in conjugation with the ester.

Synthesis of Polyfluoroalkyl Cyclobutenes from 3-Aza-1,5-enynes via an Aza-Claisen Rearrangement/Cyclization Cascade

A facile synthetic route to access polyfluoroalkyl functionalized cyclobutenes bearing an exo cyclic double bond from 3-aza-1,5-enynes is reported. The reaction proceeds via a thermal aza-Claisen rearrangement to give an allene-imine intermediate; subsequent cyclization affords the cyclobutene core. The kinetics of the transformation of starting material and the intermediate was studied by (1)H NMR spectroscopy, where a consecutive reaction was revealed.

Synthesis and Characterization of New Heptalenes with Extended π‐Systems Attached to Them

AbstractMethyl heptalenecarboxylates of type A and B with π(1) and π(2) substituents in 1,4‐relation (Scheme 1) were synthetized starting with dimethyl 1‐methylheptalene‐4,5‐dicarboxylates 5b and 6b derived from 7‐isopropyl‐1,4‐dimethylazulene (=guaiazulene) and 1,4,6,8‐tetramethylazulene by thermal reaction with dimethyl acetylenedicarboxylate. The further general way of proceeding for the introduction of the π(1) and π(2) substituents is displayed in Scheme 3, and the thus obtained methyl heptalene‐5‐carboxylates of type A and B are listed in Table 1. The CC bonds of the 2‐arylethenyl and 4‐arylbuta‐1,3‐dien‐1‐yl groups of π(1) and π(2) were in all cases (E)‐configured and showed s‐trans conformation at the CC bonds (X‐ray and 1H‐NOE evidence) in the B‐type as well as in the A‐type heptalenes (cf. Figs. 5–12).All B‐type heptalenes showed a strongly enhanced heptalene band I in the wavelength region 440–490 nm in hexane/CH2Cl2 9 : 1 (cf. Table 4 and Figs. 13–20). The A‐type heptalenes showed in this region only weak absorption, recognizable as shoulders or simply tailing of the dominating heptalene bands II/III (Table 5). Absorption band I of the B‐type heptalenes appeared almost at the same wavelength as the longest wavelength absorption band of comparable open‐chain α,ω‐diarylpolyenes (cf. Fig. 21). The cyclic double bond shift (DBS) of the A‐ and B‐type heptalenes could be photochemically steered in one or the other direction by selective irradiation (cf. Fig. 22).

Application of thiol‐ene click chemistry to preparation of functional polyethylene with high molecular weight and high polar group content: Influence of thiol structure and vinyl type on reactivity

AbstractA series of functional polyethylenes have been simply and efficiently synthesized via the combination of regioselective ethylene/5‐vinyl‐2‐norbornene (VNB) copolymerization using [PhNC(CF3)CHCO(Ph)]2TiCl2 catalyst and following ultraviolet light initiated thiol‐ene click reaction. On treatment of ethylene/VNB copolymer with different thiols including mercaptoethanol, 1‐thioglycerol, methyl mercaptoacetate, methyl mercaptopropionate, 2‐mercaptoethylamine, mercaptoacetic acid, and mercaptopropanoic acid, various polar groups have been successfully introduced into the polyethylene. Except 2‐mercaptoethylamine, the functionalizations are quite efficient with the degree of functionalization higher than 94%, which is independent of thiol structure and double bond content. The content of polar group in functional polyethylene can be tuned in a wide range of 0–30 mol %. Gel permeation chromatography profiles indicate all functional polyethylenes that have very high molecular weights (160–336 kg/mol) with homogeneous formation. Besides, systematic investigation of the influence of vinyl type and thiol structure on reactivity has been also carried out. By treatment of mercaptoethanol with different copolymers (ethylene/VNB, ethylene/5‐ethylidene‐2‐norbornene, and ethylene/dicyclopentadiene copolymer), the order of vinyl reactivity can be summarized as terminal > internal > cyclic double bond. For different thiols, the reactivity has the sequence of SHCH2COOH > SHCH2COOCH3 > SHCH2CH2COOH > SHCH2CH2COOCH3 > SHCH2CH(OH)CH2OH > SHCH2CH2OH > SHCH2CH2NH2, which is depended on the solubility and the electron‐withdrawing inductive effect of polar group. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Metabolites of the Mangrove FungusXylariasp. BL321 from the South China Sea

Two new lactones, 1 and 2, together with five known compounds, 3-7, were isolated from the marine mangrove fungus Xylaria sp. BL321. Their structures were determined by comprehensive analysis of their MS and NMR spectroscopic data. The absolute configurations of 1 and 2 were established on the basis of electronic circular dichroism calculations. It was found that the exocyclic double bond of 1 rearranged into a cyclic double bond to form a new crystal compound (1a) in diluted NaOH solution. Compound 3 was isolated for the first time as a natural product; its absolute configuration was determined by single-crystal X-ray crystallography. Compounds 4-7 displayed cytotoxicity against human breast cancer cell lines MCF-7 and MDA-MB-435, while compounds 1- 3 were inactive (IC(50) > 50 µM).

Molecular Diversity of Tonghaosu Analogues, Selective Oxidation of the exo‐Cyclic Double Bond of Spiroacetal Enol Ethers and Diasteroselective Synthesis of Spiro‐Pyranone

AbstractTwo methods including NBS/AgNO3 system and MCPBA oxidation have been developed for the selective oxidations of the exo‐cyclic double bond of spiroacetal enol ethers 2 with multi reactive sites into spiro‐pyanones 3 and 4. In addition, possible mechanisms for these conversions are proposed.

Tungsten(II)-initiated ring-opening metathesis polymerization and other C–C bond forming reactions of 5-vinyl-2-norbornene

The trichloro-bridged tungsten(II) dimer [(CO) 4W(μ-Cl) 3W(GeCl 3)(CO) 3] ( 1) has been demonstrated to be a very effective catalyst for the ring-opening metathesis polymerization (ROMP) of 5-vinyl-2-norbornene (V-NBE). The selectivity of ROMP reaction depends very strongly on properties of solvent in which the reaction is carried out. In CCl 4 solution the ROMP reaction is accompanied by the formation of small amounts of (V-NBE)-(CCl 4) adducts, but in benzene solution 2,2′-bi(vinylnorbornylidene) (bi-(V-NBE)) and (V-NBE)-(C 6H 6) adducts were also detected. In dichloromethane or chloroform- d 1 solution the selectivity of ROMP reaction is low because it is accompanied by formation of bi-(V-NBE). The tungsten(II) compound activates the more strained cyclic double bond of V-NBE. As was shown by 1H and 13C NMR spectroscopy, the pendant vinyl group is left intact in poly-(vinylcyclopentylenevinylene) as well as in bi-(V-NBE). A mechanism involving C–H bond activation of olefin and the formation of tungsta-vinylnorbornylidene is proposed to explain those results. In dichloromethane and chloroform- d 1 solution a tungsta-vinylnorbornylidene species undergoes a carbene–carbene coupling reaction to give bi-(V-NBE). The reaction products are identified by means of chromatography (GC–MS) and 1H and 13C NMR spectroscopy.

Molecular interaction study of formohydroxamic acid (FHA) with water

Ab initio and dft theoretical methods have been used to study the hydrogen bonding in the complexes formed between formohydroxamic acid (FHA) and water molecules. Eight reasonable geometries on the potential energy surface of formohydroxamic acid and water systems have been considered; four structures with three water molecules FHA-(H 2O) 3 and four structures with two water molecules FHA-(H 2O) 2. In all the complexes, the formohydroxamic acid has cis-keto form. The most stable complexes were found with cyclic double hydrogen bonds. The results of chemical hardness indicate that it does not obey maximum hardness principle (MHP) for the above hydrogen bonded systems. Two-body, three-body interaction energies and relaxation energies have been calculated by applying many-body analysis to know their role in the total interaction energy of the molecule. The results of many body analysis indicate that two-body interaction energy contribute more to the total interaction energy when compared to three-body interaction energies. Topological analysis has been performed for the complexes using Bader's Atoms in molecule theory. The topological parameters electron density and Laplacian of electron density show excellent linear correlation with the hydrogen bond length. NBO analysis have been carried out to study the charge transfer between proton acceptor to the antibonding orbital of the X-H bond in the complexes.

Molecular Diversity from Tonghaosu Analogues, Selective Reduction of theendo-Cyclic Double Bond of Tonghaosu Analogues and the Synthesis of Cyclopentenone Derivatives

The endo-cyclic double bond of unique spiroketal dienol-ether compounds 1, 2, 3 could be selectively reduced and thus obtained products could be further converted to cyclopentenone derivatives.

Studies on olefin epoxidation with t-BuOOH catalysed by dioxomolybdenum(VI) complexes of a novel chiral pyridyl alcoholate ligand

The chiral dioxomolybdenum(VI) complexes [MoCl{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}(O)2(THF)] and [Mo{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}2(O)2] have been prepared in good yields by reaction of the solvent substituted complex [MoCl2O2(THF)2] with one or two equivalents of chiral 2′-pyridyl alcohol. The optically active aminoalcohol was obtained by reaction of 2-pyridyllithium with (−)-(2S,5S)-8-trimethylsilyloxymenthone. The complexes are active catalysts in the homogeneous epoxidation of cyclic and linear olefins, dienes and terpenes by t-BuOOH. They present remarkable activity and excellent product selectivity in cyclooctene epoxidation (cyclooctene oxide was obtained in quantitative yield). In the case of limonene, regioselectivity is high in favour of the epoxidation of the internal cyclic double bond. Ring opening activity was also observed for α-pinene oxide, producing campholenic aldehyde and epoxy campholenic aldehyde.

Copolymerization of ethylene with 5-vinyl-2-norbornene in the presence of the Ph2C(Flu)(Cp)ZrCl2 /MAO catalyst

Cycloolefin copolymer, poly[(ethylene)-co-(5-vinyl-2-norbornene)], was synthetized using the MAO activated ansa-metallocene Ph2C(Flu)(Cp)ZrCl2 as a catalyst. Formation of mostly isolated 5-vinyl-2-norbornene sequences was confirmed by NMR analysis. Comonomer incorporated selectively via cyclic double bond. No selectivity towards the reactivity of the particular isomer of 5-vinyl-2-norbornene (5-endo : 5-exo) was observed. The molar mass was found to decrease when the comonomer concentration in product increased. At low comonomer incorporation levels copolymers were insoluble, cross-linked elastomers. With high comonomer concentration in reaction medium copolymers were amorphous determined by means of DSC and X-ray diffraction and the vinyl group of the comonomer remained unreacted for further modification.

2D NMR characterization of poly(ethylene-co-5-vinyl-2-norbornene)

Unsaturated poly(ethylene-co-5-vinyl-2-norbornene) was synthetized using the [Ph2C(Flu)(Cp)]ZrCl2 metallocene/methylaluminoxane (MAO) catalyst system. 1H and 13C NMR spectra of the copolymer were assigned by means of DEPT, homonuclear 2D 1H-1H COSY, and heteronuclear 2D 1H-13C correlation NMR experiments. The used catalyst system produces mainly isolated 5-vinyl-2-norbornene (VNB) sequences. VNB is incorporated selectively via the cyclic double bond. The unreacted double bond of the copolymer exists in the 5-endo: 5-exo positions (3 : 1). Both isomers of VNB are polymerized with the same propability.

2D NMR characterization of poly(ethylene-co-5-vinyl-2-norbornene)

Unsaturated poly(ethylene-co-5-vinyl-2-norbornene) was synthetized using the [Ph2C(Flu)(Cp)]ZrCl2 metallocene/methylaluminoxane (MAO) catalyst system. 1H and 13C NMR spectra of the copolymer were assigned by means of DEPT, homonuclear 2D 1H-1H COSY, and heteronuclear 2D 1H-13C correlation NMR experiments. The used catalyst system produces mainly isolated 5-vinyl-2-norbornene (VNB) sequences. VNB is incorporated selectively via the cyclic double bond. The unreacted double bond of the copolymer exists in the 5-endo: 5-exo positions (3 : 1). Both isomers of VNB are polymerized with the same propability.

Synthesis and characterization of carbon-13 labelled 2-ethylidene-5-norbornene containing EPDM rubber. Observation of crosslinking and oxidation

[2, 8- 13C 2] ENB was synthesized from labelled acetic acid and terpolymerized in a batch reactor to [2, 8- 13C 2] ENB–EPDM rubber ( M w=4.8×10 5, d=3, ENB content ∼8 wt.%, ethene to propene ratio ∼1.8). Labelled ENB, its precursors and the EPDM were characterized by NMR spectroscopy. ENB is incorporated in the polymer chain through the endo cyclic double bond. Upon high temperature exposure to air of an NMR sample, the number of double bonds decreases due to crosslinking via addition of backbone radicals to double bonds. Some oxidation of double bonds occurs, giving rise to acetyl norbornene units. No significant cleavage of double bonds takes place. The labelling/NMR approach provides an excellent tool for studying (minor) chemical conversions in EPDM rubber.