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.     

The π-Anisotropy of the Double Bond of a syn-11-Oxasesquinorbornene Derivative.. Stereoselectivity of the Diels–Alder additions of (2-norborneno)[c]furan. Crystal structure of 11-oxa-endo-tetracyclo[6.2.1.13,6.02,7]-dodec-2(7)-ene-9,10-exo-dicarboxylic anhydride

The reaction of (2-norborneno)[c]furan ( 4 ) with maleic anhydride gave 11-oxa-endo-tetracyclo[6.2.1.1^3,6.0^2,7]dodec-2(7)-ene-9,10-exo-dicarboxylic anhydride ( 5 ) and, with methyl acetylenedicarboxylate, methyl 11-oxa-endo-tetracyclo [6.2.1.1^3,6.0^2,7]dodeca-2(7),9-diene-9,10-dicarboxylate ( 7 ). The syn-11-oxa-sesquinorbornenes 5 and 7 could be equilibrated with their cycloaddents. They are at least 2 kcal/mol more stable than the corresponding anti-sesquinorbornenes 6 and 8 . The structure of 7 was deduced from its spectral data, by epoxidation with air or a peracid to give the exo-epoxide 13 and by catalytic hydrogenation to give 14 . The structure of 5 was established by single-crystal X-ray diffraction. A dihedral angle of 163° was measured between the C(1,2,7,8) and C(2,3,6,7) planes in 5 . This important deviation from planarity for the C(2,7) double bond is attributed to (π, ω)-repulsive interactions that make the π-electron density of 2-norbornene and 7-oxa-2-norbornene derivatives preferentially polarized toward the exo-face. This finding is discussed in relation with the relative stability of the syn- and anti- 11-oxasesquinorbornenes and with the endo-stereoselectivity of the cycloadditions of the norbornenofuran 4 .     

Nucleophilic addition to C,C?double bonds. Part IX. Kinetics and mechanism of the base-catalyzed intramolecular cyclization of olefinic alcohols

The base-catalyzed intramolecular cyclization of polycyclic olefinic alcohols of type a (10-endo-hydroxy-anti^9,10-tricyclo [4.2.1.1^2,5]dec-7-en-9-ones (type h ), anti^9,10-tricyclo[4.2.1.1^2,5] dec-3-en-9-endo-ols (type j ), and anti^10,11-tricyclo[4.3.1.1^2,5]undec-3-en-10-endo-ols (type 1 )) to the ethers d and f , resp., has been studied. A mechanism for the nucleophilic addition of the corresponding alkoxide anion b to the isolated C,C? double bond is discussed. It is proposed that b is formed (fast acid/base equilibrium) in the first step. For the subsequent reaction sequence, there are two well distinguishable pathways: (a) Compounds with an additional carbonyl group ( h ) cyclize via a homoenolate-like intermediate c , which is protonated stereoselectively on the exo-side by the hydroxylic solvent. (b) Compounds without a carbonyl group ( j and l ) cyclize 10²-10⁴ times slower, and the reaction proceeds via a carbanion-like transition state e . The proton transfer from the hydroxylic solvent is clearly coupled with the C,O? bond formation. Steric compression in the olefinic alcohols a influences the cyclization rate: (a) Alcohols with a smaller ring ( h , X = CH₂CH₂) cyclize 70–200 times faster than the ones with a larger ring ( 1 , X = CH₂CH₂CH₂). (b) Replacement of the H-atom at the carbinol C-atom by a CH₃ group enhances the rate of ether formation by a factor of 50–100. Due to through-bond interactions between the C,C-double bonds, olefinic alcohols with an additional endocyclic C,C-double bond ( h and j , X = CH?CH) cyclize 20–300 times faster than the corresponding monoolefinic ones ( h and j , X = CH₂CH₂).     

The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part IV. Hydride-ion abstraction in 1,2-exo-trimethylenenorbornane

In the AlBr₃-catalyzed adamantane rearrangement in CS₂ of 1,2-exo-trimethylenenorbornane ( 1 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ), hydride-ion abstraction occurs at C(6) from the exo-side. The k_H/k_D value for competition between 1 and 5 (D_exo-C(6)) was 1.58 ± 0.05, whereas no kinetic isotope effect was operative for competition between unlabeled 1 and 4 (D_endo-C(5)) and between 1 and 6 (D_endo-C(6)).     

Living Carbocationic Polymerization. LVII. Kinetic Treatment of Living Carbocationic Polymerization Mediated by the Common Ion Effect

Abstract

The effect of anion concentration on the apparent rate constant of polymerization k^A _p of isobutylene (IB) induced by the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system using the CH₂Cl₂/nC₆H₁₄ (60/40 v/v) solvent system at ?40 and ?80°C was studied by the use of nBu₄NCl. Computer simulation has shown that k^A _p decreases several orders of magnitude upon the addition of even a very small amount of common anion TiCl^?- ₅ to the charge. The rate of change is reduced in the concentration range of experimental interest. It was concluded that the decrease of k^A _p with increasing TiCl ^?- ₅ concentration is mainly due to the decreasing contribution of propagation by free ions. The contribution (%) of propagation by free ions to the apparent rate of propagation was calculated.     

A Cascade Synthesis of Hetero‐arylated Triarylmethanes Through a Double 5‐endo‐dig Cyclization Sequence

A sequential two‐step method for the synthesis of hetero‐arylated triarylmethanes through a Ag‐catalyzed sequential double cyclization–nucleophilic addition cascade is described. This methodology basically involves an initial 5‐endo‐dig cyclization of o‐alkynyl anilines to provide 2‐substituted indole derivatives, which then react with 2‐(2‐enynyl)‐pyridines to afford indolizine‐containing unsymmetrical triarylmethanes through another 5‐endo‐dig cyclization.     

A highly efficient radical clock as a probe of the mechanism of sulfone halogenation by perhaloalkanes

Halogenation of (endo)-5-(2-i-propylsulfonyl)-2-norbornene 5, a new highly efficient radical probe, shows that if an SET mechanism was occurring in the -α-halogenation of sulfones by perhaloalkanes, it would have to involve a reaction step in which a C-centered radical reacts with CX₄^$\text{.}$ at a rate greater than 10¹⁰ s^?1.     

Gold‐Catalyzed Cyclization of Diynes: Controlling the Mode of 5‐endo versus 6‐endo Cyclization—An Experimental and Theoretical Study by Utilizing Diethynylthiophenes

Herein, a dual‐gold catalyzed cyclization of 3,4‐diethynylthiophenes generating pentaleno[c]thiophenes through gold–vinylidenes and C?H bond activation is disclosed. Various new heteroaromatic compounds—substrate classes unexplored to date—exhibiting three five‐membered annulated ring systems could be synthesized in moderate to high yields. By comparison of the solid‐state structures of the corresponding gold–acetylides, it could be demonstrated that the cyclization mode (5‐endo versus 6‐endo) is controlled by the electronic and not steric nature of the diyne backbone. Depending on different backbones, we calculated thermodynamic stabilities and full potential‐energy surfaces giving insight into the crucial dual‐activation cyclization step. In the case of the 3,4‐thiophene backbone, in which the initial cyclization is rate and selectivity determining, two energetically distinct transition states could be localized explaining the observed 5‐endo cyclization mode by classical transition‐state theory. In the case of vinyl and 2,3‐thiophene backbones, the theoretical analysis of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition‐state theory is no longer valid to explain the high experimentally observed selectivity. Herein, for the first time, the influence of the backbone and the aromatic stabilization effect of the 6‐endo product in the crucial cyclization step could be visualized and quantified by calculating and comparing the full potential‐energy surfaces.     

Regioselective radical cyclization initiated by the reaction of allylic hydroperoxides with iron(II) sulfate

Treatment of 1-methyl-2-methylene-1-cyclohexyl hydroperoxide with a mixture of FeSO₄/CuCl₂ yielded 1-(1-chlorocyclohexyl)ethanone as the major product consistent with 6-endo-trig cyclization of the intermediate 5-acetylhex-5-enyl radical. This strategy was extended to the ring enlargement of a series of 1-isopropenylcycloalkyl hydroperoxides. Regioselective 7- or 8-endo-trig cyclization reactions could be achieved by treatment of the corresponding cyclopentyl or cyclohexyl hydroperoxides with either a mixture of FeSO₄/CuCl₂ or with FeSO₄ only. The influence of substituents on the efficiency of the 8-endo-trig cyclization process was also explored.     

Norbornanes. Part 18. Inductive Charge Dispersal in the Solvolyses of 4- and 5-Substituted 2-Norbornyl p-Toluenesulfonates

The solvolysis rates and products of 4- and 5-exo-substituted 2-exo- and 2-endo-norbornyl tosylates 9 and 10 , respectively, are reported. The logarithms of the rate constants (log k) correlate linearly with the inductive constants σ for the substituents. A comparison of the reaction constants p₁ for the 4-, 5-, 6-, and 7-substituted 2-exo- and 2-endo-tosylates 9 , 10 , 1 , and 2 respectively, indicates that inductivity is higher for 2-exo-ionization than for 2-endo-ionization in all series. This observation is attributed to the more favorable alignment of neighbouring C-atoms for dorsal participation in exo-ionization, especially, in the case of C(6).     

The preparation and structure of 1,4,5,6,7,7-hexachloro-2-endo-ferrocenylhydroxymethyl-3-endo-hydroxymethyl-5-norbornene

The crystal structure of a novel ferrocene derivative with potential flame-retardant/smoke-suppressant activity, 1,4,5,6,7,7-hexachloro-2-endo-ferrocenyl-hydroxymethyl-3-endo-hydroxymethyl-5-norbornene, has been determined. Some of the carbon–carbon bonds within the chlorendic residue are unusually long, and there is no interaction between the hydroxyl groups and the iron atom. There is evidence of intramolecular hydrogen bonding between the two hydroxyl groups.     

Mechanistic Insights about the Ligand-Enabled Oxy-arylation/vinylation of Alkenes via Au(I)/Au(III) Catalysis

The mechanism of oxy-arylation/vinylation of alkenes catalyzed by the (MeDalphos)AuCl complex was comprehensively investigated by DFT. (P,N)Au(Ph)²⁺ and (P,N)Au(vinyl)²⁺ are key intermediates accounting for the activation of the alkenols and for their cyclization by outer-sphere nucleophilic attack of oxygen. The 5-exo and 6-endo paths have been computed and compared, reproducing the peculiar regioselectivity difference observed experimentally between 4-penten-1-ol, (E) and (Z)-4-hexen-1-ols. Examining the way the alkenol coordinates to gold (more η² or η¹) can offer, in some cases, a simple way to predict the favored path of cyclization.     

The Novel Adamantane Isomer Tricyclo[4.4.0.03,9]decane (2-Homotwistbrendane)

Two synthetic approaches to the novel C₁₀H₁₆ hydrocarbon tricyclo[4.4.0.0^3,9]decane ( 1 ; 2-homotwistbrendane), one of the 19 members of the adamantaneland, and its Lewis-acid-catalyzed rearrangement are described. One route starts from tricyclo[4.3.0.0^3,8]nonan-2-one ( 2 ; 2-twistbrendanone). The missing tenth C-atom is introduced by ring enlargement (Tiffeneau-Demjanov method). Starting from methyl 8,9,10-trinorborn-5-ene-2-endo-carboxylate ( 8 ), ring enlargement by one C-atom, regio- and stereoselective introduction of a C₁ unit to a 2-endo,6-endo-disubstituted bicyclo[3.2.1]octane, and ring closure by acyloin condensation are the key steps in the second approach.     

Secondary Deuterium Isotope Effect in an Electrophilic Aromatic Substitution - Protodesilylation of Trimethylphenylsilane

Reaction rates for the protodesilylation of trimethylphenylsilane and of [2,4,6-²H₃]-trimethylphenylsilane by HCIO₄, were measured in aqueous methanol (2:5, v/v) and the secondary deuterium isotope effect for the reaction was found to be k_H/k_D3 = 0.79. The magnitude of the observed isotope effect supports a mechanism in which the rate-determining step is the proton transfer from the hydronium ion to the silane to form a σ-intermediate.     

Effects of Remote Substitution on the Photo-oxidation of Exocyclic s-cis-Butadienes Grafted onto Bicyclo [2.2.1]heptanes. Thermal and Rhodium Catalyzed Rearrangements of 3,6-Dihydro-1,2-dioxines

The rates of photo-oxidation of exocyclic S-cis-butadienes grafted onto bicyclo-[2.2.1]heptanes and 7-oxabicyclo[2.2.1]heptanes ( 1–6 ) are dependent upon remote modifications of the bicyclic skeletons. They correlate with the rates of Diels-Alder additions of these dienes to strong dienophiles. The 2,3-dimethylidenenorbornane ( 1 ), 5,6-dimethylidene-2-norbornene ( 2 ) and 2,3-dimethylidene-7-oxanorbornane ( 3 ) gave the corresponding endo-peroxides (3,6-dihydro-1,2-dioxines) 7–9 in good yield. The 2, 3, 5, 6-tetramethylidene-7-oxanorbornane ( 4 ) gave the mono-endo-pe-roxide 6 , the latter did not react with a second equivalent of oxygen. Similarly, 5, 6-dimethylidene-7-oxa-2-norbornene ( 5 ) was unreactive toward photo-oxidation. Thermal isomerization of the endo-peroxides 7 and 9 gave, the trans-diepoxides 10 and 14 , respectively, with high stereoselectivity. The endo-peroxides 6 , 7 and 9 were cleanly isomerized into the corresponding α, β-unsaturated γ-hydroxy aldehydes in the presence of catalytic amounts of Rh₂(CO)₄Cl₂.     

Influence of fluorine substitution on the molecular conformation of 3′‐deoxy‐3′‐fluoro‐5‐methyluridine

Fluorine substitutions on the furanose ring of nucleosides are known to strongly influence the conformational properties of oligonucleotides. In order to assess the effect of fluorine on the conformation of 3′‐deoxy‐3′‐fluoro‐5‐methyluridine (^RT^F), C₁₀H₁₃FN₂O₅, we studied its stereochemistry in the crystalline state using X‐ray crystallography. The compound crystallizes in the chiral orthorhombic space group P2₁2₁2₁ and contains two symmetry‐independent molecules (A and B) in the asymmetric unit. The furanose ring in molecules A and B adopts conformations between envelope (²E, 2′‐endo, P = 162°) and twisted (²T₃, 2′‐endo and 3′exo, P = 180°), with pseudorotation phase angles (P) of 164.3 and 170.2°, respectively. The maximum puckering amplitudes, ν_max, for molecules A and B are 38.8 and 36.1°, respectively. In contrast, for 5‐methyluridine (^RT^OH), the value of P is 21.2°, which is between the ³E (3′‐endo, P = 18.0°) and ³T₄ (3′‐endo and 4′‐exo, P = 36°) conformations. The value of ν_max for ^RT^OH is 41.29°. Molecules A and B of ^RT^F generate respective helical assemblies across the crystallographic 2₁‐screw axis through classical N—H…O aand O—H…O hydrogen bonds supplemented by C—H…O contacts. Adjacent parallel helices of both molecules are linked to each other via O—H…O and O…π interactions.     

自由基环化制备β-内酰胺的理论研究

使用密度泛函方法在UB3LYP/6-311＋＋G(3df, 2p)水平上对自由基环化合成β-内酰胺的四种反应途径进行理论研究. 结合Marcus理论对影响反应的热力学及动力学因素进行分析, 发现氨基甲酰基自由基4-exo环合反应是理想的动力学控制过程; 酰胺自由基的4-exo环合反应与5-endo环合反应相比是动力学有利的转化过程; 单取代的酰胺烷基自由基的4-exo环合反应是一类动力学和热力学都较为不利的反应; 羰基自由基加成亚胺N＝C双键的4-exo环合反应与5-endo环合反应相比动力学不利而热力学有利.     

Zur Konfiguration der 2,4,6,8-Tetrabrom-cyclooctan-1,5-dione Reduktion des β-Isomers durch Natrium-borhydrid

Of the two previously described 2,4,6,8-tetrabromo-cyclooctane-1,5-diones, the higher melting β-isomer, mp. 226°, was treated with sodium borohydride to give: (1) by a double reduction and an intramolecular S_N2-reaction two epimeric alcohols, namely the 2-exo-hydroxy- ( 6 ) and 2-endo-hydroxy- ( 7 ) isomers of 3-exo,5-exo,7-endo-tribromo-9-oxa-bicyclo[4.2.1]nonane, and (2) by a single step reduction a hemiketal, 1-hydroxy-2-exo,4-exo,6-endo,8-endo-tetrabromo-9-oxa-bicyclo[3.3.1]nonane ( 8 ). The structures of these three hydroxy-compounds ( 6, 7 and 8 ) were derived from their properties, especially from complete analyses of their NMR.-spectra, which led to deductions of all configurations and conformations. Of special interest is the preferred existence of the 9-oxa-bicyclo[3.3.1]norane derivative 8 in a chair-chair conformation. The derivation of the configurations of the three hydroxy-compounds 6, 7 and 8 is tantamount to establishing the 2,4-cis, 4,6-trans, 6,8-cis-configuration ( 5 ) of the β-isomer of 2,4,6,8-tetrabromocyclooctane-1,5-dione, mp. 226°.     

The analytical resolution of parallel first‐ and second‐order reaction mechanisms

Given the species A₁ and A₂, the competition among the three different elementary processes (1) (2) (3) is frequently found in thermal and photochemical reaction systems. In the present paper, an analytical resolution of the system (1)–(3), performed under plausible contour conditions, namely, finite initial molar concentrations for both reactants, [A₂]₀ and [A₁]₀, and nonzero reaction rate coefficients k₁, k₂, and k₃, leads to the equation [A₁] = ((δ[A₂]^γ ? [A₂])/β) ? α, where α = k₁/2k₃, γ = β + 1 = 2k₃/k₂, and δ = ([A₂]₀ + β[A₁]₀ + β α))/[A₂]₀^γ. The comparison with a numerical integration employing the fourth‐order Runge–Kutta algorithm for the well‐known case of the oxidation of organic compounds by ferrate ion is performed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 562–566, 2010     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Influence de la concentration en bromure et rôle du solvant sur la réactivité des anisoles au cours de la réaction de bromation

Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO₂, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br₂ and Br^?₃ present as the A⁺Br^?₃ form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br₂] [A⁺Br^?]_T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of k^o,p_g {1 + K′[A⁺Br^?]_T}VS[A⁺Br^?]_T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO₂ helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO₂ than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p⁺_p = ?7.83; p⁺_o= ?10.47).