Application of the semilocalized approach to chemical reactivity of butadiene

The semilocalized approach to chemical reactivity (J. Mol. Struct. (Theochem) 588 (2002) 99; Int. J. Quant. Chem. 94 (2003) 302) is applied to study the addition reaction of an electrophile or nucleophile to the butadiene molecule. In accordance with the classical concept of the reaction center and its neighborhood (substituent), only one of the two H₂C=CH-fragments of butadiene is supposed to be under a direct attack of the reagent, whereas the remaining H₂C=CH-group is assumed to play the role of the substituent and thereby to participate in the process indirectly by exerting certain electron-donating or accepting effect upon the former group and/or the reagent. The main aim of the study consists in revealing the role of the H₂C=CH-substituent in the formation of the known higher reactivity of the terminal carbon atom of the attacked C=C-bond (as compared to the internal atom) irrespective of the nature of the reagent. To this end, we seek to obtain an explicit algebraic representation of the interdependence between the direction and the extent of the total influence of the H₂C=CH-substituent, on the one hand, and the nature of the reagent, on the other hand. The expressions for electron density and bond order redistributions among separate fragments of contacting molecules derived previously in the form of power series are shown to yield the above-anticipated representation. On this basis, it is demonstrated that the electron-donating effect of the initially occupied (bonding) orbital of the substituent and the electron-accepting effect of its initially vacant (antibonding) orbital upon the remaining fragments of the whole reacting system may be considered independently whatever the nature of the reagent. However, a strong interdependence is established between the actual relative extents of these two components of the total effect of the H₂C=CH-group and the electron-donating (accepting) properties of the reagent. Moreover, this group of atoms is shown to manifest itself as an electron-donating (accepting) substituent under influence of an electrophilic (nucleophilic) attack. Using this principal result of the paper, the actual reactivity of butadiene with respect to electrophile (nucleophile) is interpreted by invoking a model system of a substituted ethene containing a simple (one-orbital) electron-donating (accepting) substituent, and a terminal addition easily follows for both types of the reagent.     

Hydrogen Effect on Coke Removal and Catalytic Performance in Pre-Carburization and Methane Dehydro-Aromatization Reaction on Mo/HZSM-5

1. Introduction As an effective utilization of methane, the methane dehydro-aromatization was focused in the last decade [1-28]. Over the Mo/HZSM-5 bi- functional catalyst at high reaction temperature, methane can be converted into light aromatics (ben- zene and naphthalene) and hydrogen. Mo active species can activate the C—H bond of methane; and HZSM-5 supplies the acid sites for the oligomeriza- tion and cyclization of hydrocarbons to form aromat- ics, and suppresses the deeper condens…     

Preparation of polyfluorinated cycloalk-1-enyl-, alk-1-enyl-, and alkyliodine tetrafluorides using XeF2 in the presence of appropriate Lewis acids as fluorooxidant

Previously unknown polyfluorocyclohexenyl, and acyclic perfluoroalkenyliodine tetrafluorides were prepared in high yields. Perfluorocyclohex-1-enyliodine tetrafluoride was obtained from pentafluoroiodobenzene using XeF₂-NbF₅ in aHF. The reaction of C₆F₅I with the weaker fluorooxidant XeF₂-BF₃ in 1,1,1,3,3-pentafluorobutane (PFB) yielded C₆F₅IF₂, perfluorocyclohexa-1,4-dienyliodine difluoride, C₆F₅IF₄, perfluorocyclohexa-1,4, and 1,3-dienyliodine tetrafluoride as intermediate products on parallel reaction routes. Both perfluoroalkenyl iodides, cis- and trans-(CF₃)₂CFCFCFI, reacted with XeF₂-BF₃ in PFB to give the corresponding perfluoroalkenyliodine tetrafluorides, cis- and trans-(CF₃)₂CFCFCFIF₄. Even perfluoroalkyl iodides can be fluorinated by this reagent as was demonstrated by the preparation of C₆F₁₃IF₄ from C₆F₁₃I. Generally, the CFCIF_n fragment (n = 0, 2, or 4) in cyclic or acyclic perfluoroalkenyliodine compounds R_FIF_n did not undergo a transformation to the corresponding perfluoroalkyliodine compound. Furthermore, no perfluoroorganoiodine hexafluorides were detected in reactions with the fluorooxidant XeF₂-aHF or BF₃ or NbF₅.     

The furan approach to oxacycles. Part 5: Synthesis of a chiral butenolide, building block towards biologically interesting natural products

We describe an efficient new approach for the synthesis of a chiral butenolide that is based on the oxidation of a chiral furan ring with singlet oxygen in the presence of Hünig’s base, followed by Luche reduction and in situ lactonization.     

Tandem asymmetric conjugate addition-enolacetates formation of enantiomerically enriched zinc and aluminium enolates

The metal enolates, resulting from the copper-catalyzed enantioselective conjugate addition of organometallic reagents (Et₂Zn or R₃Al) to cyclic and acyclic enones are quantitatively trapped as enolacetates with acetic anhydride.     

Stereoselective effects in the solid-phase hydrogenation of unsaturatedl-hydroxyproline derivatives

The solid-phase catalytic hydrogenation of (R-4tert-butoxy-Δ¹-pyrroline-2-carboxylic) acid under the action of hydrogen spillover was studied. The reaction proceeds stereoselectively with the predominant formation of thel-amino acid. The configuration of the asymmetric center formed is determined by that of the asymmetric C(4) atom. The major portion of the isotope label is incorporated into the allylic C(3) and C(5) positions, and the β-H atoms are more mobile. Using quantum-chemical calculations, the geometric structure of thel-hydroxyproline molecule was calculated, and the spin-spin coupling constants for this tritium-labeled amino acid were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1820–1823, October, 1997.     

Regio- and Stereocontrolled Nucleophilic Addition Reactions of An Unsymmetrically Disbustituted Butadiene η4-Molybdenum Cationic Complex

The reactions of a new cationic complex, [Cp(CO)₂Mo(η⁴-2-methyl-3-SPh-C₄H₄)]⁺ PF^?₆ (3), with carbon, hydride, and nitrogen nucleophiles were found to give only the C-1 addition products in good yield. The X-ray crystal structures of two of the addition products 4a and 4e confirm the regio- and stereochemistry of the nucleophilic additions.     

PS-b-P4VP两嵌段共聚物的合成及其自组装的研究

双硫酯 (PhC(S)SCH2 Ph)作为链转移剂 ,AIBN作为引发剂 ,用可逆的加成 断裂链转移 (RAFT)活性自由基聚合方法 ,合成了PS大分子链转移剂 .然后在AIBN引发下 ,利用制得的大分子链转移剂 ,以DMF为溶剂 ,80℃下采用RAFT方法 ,合成了PS b P4VP两嵌段共聚物 ,通过核磁共振谱及动力学的研究证明了其活性聚合的特征 .结果表明聚合反应在 2 4h内转化率可达 95 % .并用透射电子显微镜 (TEM )和扫描电子显微镜(SEM)研究了PS b P4VP两嵌段共聚物在选择性溶剂硝基苯 四氢呋喃中的自组装行为 ,研究结果表明改变聚合物的浓度以及选择性溶剂 ,可观察到自组装行为的变化 .     

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for Michael addition of mercaptans to α,β-unsaturated carbonyl compounds

Copper(II) tetrafluoroborate has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under solvent-free conditions and in H₂O at room temperature. The reactions are very fast and are completed in 2 min to 1 h affording high yields. The rate of thiol addition was dependent on the steric hindrance at the β-carbon of the α,β-unsaturated carbonyl substrate. In the case of chalcones, the reactions are best carried out in MeOH as solvent.     

Theoretical study of the reaction of alkynes with furan catalyzed by AuCl3 and AuCl

A general scheme for the endo‐ and exo‐cyclization of furan reactivity with [L ‐Au^{III, I}Cl_x] with (x = 3, 1 and L ‐acetylene and vinylidene) complexes is investigated using density functional theory (DFT) code. Two conceivable mechanisms via a [4 + 2] Diels–Alder process or carbene complex are analyzed. According to the activation energy values of the gold (III and I) catalyst, the first mechanism, which implies the Diels–Alder reaction of Au^III, is thermodynamically favored and gives more evidence of the intramolecular addition of the furan with the alkynes. The second mechanism, presumably assisted by the spontaneous formation of the exo‐vinylidene complexes and intermediates of gold (III, I) by forming the carbene complex, is kinetically favored. Additionally, we compare our results with other structures with intramolecular additions that exhibit the quasi‐similarity of gold analogue structures. Differences in activation energies are observed, according to the functional used. Finally, we probe the solvent effects, which decrease the energy barrier in the path. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007