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1.
Density functional (B3LYP) calculations using the 6-31++g basis set have been employed to study the title reaction between the cationic 1,3-dipolar 1-aza-2-azoniaallene ion (H2C=N(+)=NH) and ethene. Our calculations confirmed that [3 + 2] cycloaddition reaction takes place via a three-membered ring intermediate. In addition, solvent effects and substituent effects were also studied. For the reactions involving tetrachloroethene, there are two attacking sites. One is on the NH group in the 1-aza-2-azoniaallene ion, another is on its terminal CH2 group, and they are competitive for both approaching positions. Electron-releasing methyl substituents on ethene favor the reaction, and the potential energy surface is quite different from the previous one. 相似文献
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Theoretical studies on cycloaddition reactions between 2-azoniaallene cations and olefins 总被引:6,自引:0,他引:6
The mechanisms of cycloaddition reactions between 2-azoniaallene cations and olefins have been explored at the B3LYP/6-31G level. It is found that the positive charge in 2-azoniaallene makes the reaction more complicated. For the reactions between olefins with Cl groups or CH(3) groups and 2-azoniaallene, the typical carboniums have been located along the reaction path. In addition, for the reactions between 1,1-dimethylethene and 1,3-dichrolo-2-azoniaallene, different paths and products have been rationalized and verified. 相似文献
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Theoretical studies on cycloaddition reactions between keteniminium cations and olefins 总被引:1,自引:0,他引:1
The mechanisms of seven reactions between keteniminium cations and olefins have been theoretically explored at BHandHLYP/6-31G level. It is found that these seven reactions always form a relatively stable hydrogen-bonded type of ion-molecule complex first except for reactions 1d+2a and 1e+2a, which have no hydrogen atom attached to nitrogen atom in keteniminium cations. Some reactions take place via a concerted but unsynchronous mechanism, and the others are stepwise processes. The substituent effects are also studied. The data reveal that the electron-pushing substituents on keteniminium cations disfavor the reaction, and the electron-attracting substituents on keteniminium cations favor the reactions. The substituent effects on ethene are contrary to the former case. 相似文献
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The 1,3-butadiene radical cation reacts with acrolein and methyl vinyl ketone to produce ‘stable’ adducts. The nature of the reaction and the structures of the adducts were investigated by collisional activation decomposition (CAD) combined with tandem mass spectrometry (MS/MS), and also by Fourier transform mass spectrometry. The CAD spectra of gas-phase adducts were compared with those of suitable model compounds. On that basis, it was determined that the 1,3-butadiene radical cation undergoes a cycloaddition with these α,β-unsaturated carbonyl compounds. The butadiene radical cation serves as the ‘ene’, and the acrolein and methyl vinyl ketone react as dienes, forming cycloadducts having 2-ethenyl-2,3-dihydropyran radical cation structures. 相似文献
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Diels-Alder cycloaddition of s-trans-1,3-butadiene (1) should yield trans-cyclohexene (7), just as reaction of the s-cis conformer gives cis-cyclohexene (9). Investigation of this long-overlooked process with Hartree-Fock, Moller-Plesset, CASSCF, and DFT methods yielded in every case a C(2)-symmetric concerted transition state. At the B3LYP/6-31G (+ZPVE) level, this structure is predicted to be 42.6 kcal/mol above reactants, while the overall reaction is endothermic by 16.7 kcal/mol. A stepwise diradical process has been studied by UBLYP/6-31G theory and found to have barriers of 35.5 and 17.7 kcal/mol for the two steps. Spin correction lowers these values to 30.1 and 13.0 kcal/mol. The barrier to pi-bond rotation in cis-cyclohexene (9) is predicted (B3LYP theory) to be 62.4 kcal/mol, with trans-cyclohexene (7) lying 53.3 kcal/mol above cis isomer 9. Results suggest that pi-bond isomerization and concerted reaction may provide competitive routes for Diels-Alder cycloreversion. It is concluded that full understanding of the Diels-Alder reaction requires consideration of both conformers of 1,3-butadiene. 相似文献
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M. Yu. Krysin I. K. Anokhina L. P. Zalukaev 《Chemistry of Heterocyclic Compounds》1987,23(11):1166-1169
A carbonyl ylid, which reacts with maleic anhydride, N-phenylmaleinimide, and -nitrostyrene to form adducts resulting from 1,3-dipolar cycloaddition, is formed reversibly when 2-benzylideneindan-1,3-dione -oxide is heated (80C). The reaction proceeds regio- and stereospecifically.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1463–1466, November, 1987. 相似文献
10.
The title fluorodiene (2) reacts with several dienophiles in moderate yields (20-65%, 0.5 h to 3d) when thermal activation is used. When 100 W microwave radiation is used the reaction yields (70-90%, 5-25 min) are greatly improved and the reaction times are much shorter. A microwave procedure is also used for the hydrolysis of vinyl ether cycloadducts to alpha-fluoroketones. 相似文献
11.
《Tetrahedron》1986,42(22):6235-6244
Mass spectrometric techniques are now used extensively for the study of gas-phase radical cation chemistry. The generation and structural properties, the unimolecular and bimolecular chemistry of some representative radical cation systems, and the methods of study are reviewed. The structure of the ionmolecule adduct produced in the reaction of the benzene radical cation and neutral 1,3-butadiene was investigated by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition spectrum. The CAD spectrum of the adduct changes dramatically as a function of the degree of collisional stabilization. This observation is interpreted in terms of two distinct structures for the adduct. The species that is stabilized at 0.7 Torr has a CAD spectrum similar to the 2-phenyl-2-butene radical cation. The second structure, stabilized at 0.1 Torr, has a CAD similar to that of 1-methylindan. The results of these experiments are interpreted in terms of a two-step cycloaddition mechanism for the formation of the 1-methylindan radical cation. 相似文献
12.
Bongkoch Tarnchompoo Chachanat Thebtaranonth Yodhathai Thebtaranonth 《Tetrahedron letters》1987,28(52):6671-6674
The preparation of 2,3-dicarbomethoxy-1,3-butadiene from flash vacuum pyrolysis of
(itself obtained from methylenation of
) is described. The diene's reactions with nucleophiles and dienophiles are also reported. 相似文献
13.
2-Trimethylsilylmethyl and 2-trimethylstannylmethyl-1,3-butadiene undergo facile cycloaddition with dienophiles, and show high regioselectivity with unsymmetrical dienophiles. 相似文献
14.
Dennis C. Van Landuyt Samuel F. Reed 《Journal of polymer science. Part A, Polymer chemistry》1971,9(2):523-529
The polymerization behavior of 1-ferrocenyl-1,3-butadiene has been investigated by using both free-radical and anionic initiation techniques. Polymerization occurred readily under the promoting action of butyllithium; however, no polymerization occurred when azobisisobutyronitrile (AIBN) or benzoyl peroxide was employed as initiator. Copolymerizations were carried out with methyl methacrylate and styrene. The behavior of 1-ferrocenyl-1,3-butadiene in the copolymerizations was followed by dilatometric rate measurements, solution viscosity determinations, and elemental analysis. The major effect observed was a severe reduction in the intrinsic viscosities of the copolymers. An explanation for the observed behavior of 1-ferrocenyl-1,3-butadiene in these reactions is advanced. 相似文献
15.
Dennis J. Bellville Ronald Chelsky Nathan L. Bauld 《Journal of computational chemistry》1982,3(4):548-551
The conversion of the cyclobutene cation radical to the 1,3-butadiene cation radical has been studied using MINDO /3 and ab initio SCF MO methods. Not only smooth electrocyclic but also stepwise, non-electrocyclic routes were considered. Both calculational methods agree that the preferred reaction path is a novel nonelectrocyclic one proceeding through an intermediate “cyclopropylcarbinyl cation radical.” The quantitative agreement in the activation parameters calculated by the two methods is excellent. The proposed intermediate also provides an attractive explanation for the mass spectrometric fragmentation patterns of the cyclobutene and butadiene cation radicals. 相似文献
16.
Adriana B. Pierini Mario G. Cardozo Aida A. Montiel Sem M. Albonico Maria T. Pizzorno 《Journal of heterocyclic chemistry》1989,26(4):1003-1008
We report a 1,3-dipolar cycloaddition reaction between a oxazolium 5-oxide derivative with chloroacrylonitrile or ethyl propiolate as dipolarophiles, in order to obtain substituted pyrrolizidines. Experimentally we found that the reaction is regiospecific with chloroacrylonitrile and regioselective with ethyl propiolate. The secondary attractive orbital interactions from the Frontier Molecular Orbital Theory, the differences in stability of the possible biradical intermediaries postulated for the reaction and some hindrance effects, explain the regioselectivity observed experimentally. 相似文献
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E. Malamidou-Xenikaki X. N. Stampelos E. Coutouli-Argyropoulou 《Journal of heterocyclic chemistry》1996,33(3):563-567
Reactions of the in situ prepared 1-methylindol-2-yl nitrile oxide ( 2a ) with dipolarophiles lead to isoxazolines 5 and isoxazoles 8 and to their chloro-derivatives 6 and 9 in good yields. Analogous reactions of the 1,3-dimethylindol-2-yl nitrile oxide ( 2b ) give the isoxazolines 10 and the isoxazoles 12 as main products as well as their oxidation products 11 and 13 in low yields. The mechanism of the reactions and the spectral elucidation of the cycloadducts are discussed. 相似文献