3008-13-7Relevant academic research and scientific papers
THE INFLUENCE OF CAPTODATIVE EFFECT ON THE DIENOPHILICITY OF OLEFINS. THE EASY DIELS-ALDER REACTION OF α-METHYLTHIOACRYLONITRILE WITH CYCLOHEXADIENE
Boucher, Jean-Luc,Stella, Lucien
, p. 5041 - 5044 (1985)
We show that the cycloaddition of α-methylthioacrylonitrile to cyclohexadiene is faster than that of acrylonitrile.This indicates that the captodative substitution exerts an accelerating effect on the Diels-Alder reaction despite the larger steric bulk of the methylthio group compared to hydrogen.
Orbital unsymmetrization of olefins arising from non-equivalent orbital interactions. σ-π Coupling in bicyclo[2.2.2]octenes
Ohwada, Tomohiko,Uchiyama, Masanobu,Tsuji, Motonori,Okamoto, Iwao,Shudo, Koichi
, p. 296 - 306 (2007/10/03)
We characterized experimentally the substituent effect of a 5-exo substituent on the π facial selectivities of bicyclo[2.2.2]octenes toward electrophilic oxidative reactions such as epoxidation and dihydroxylation, and we discuss the underlying orbital interactions of vicinal σ orbitals and the olefinic π orbital involved in bicyclo[2.2.2]octenes, and commonly in methylenenorbornanes. Of significance is the out-of-phase motif of these σ- π couplings. Electron-withdrawing substituents such as cyano and carboxylic acid groups unequalize the relevant σ-π coupling, leading to the observed syn-facial preference. Alkyl substituents exhibit an electron-donative perturbing effect, depending on the bicyclic ring system.
Evidence for 2-Hexene-1,6-diyl Diradicals Accompanying the Concerted Diels-Alder Cycloaddition of Acrylonitrile with Nonpolar 1,3-Dienes
Li, Yufei,Padias, Anne Buyle,Hall, H. K.
, p. 7049 - 7058 (2007/10/02)
The spontaneous reactions of a series of alkyl 1,3-dienes with acrylonitrile (AN) were investigated.Reproducible spontaneous copolymerizations were shown to compete with the expected concerted cycloadditions.For dienes which exist in s-cis/s-trans equilibrium, both copolymer and cycloadduct are formed.Kinetic measurements show that the alternating copolymerization and cycloaddition are two independent paralell second order reactions.With 1,3-cyclohexadiene and 1,2-dimethylenecyclohexane, for which s-gauche is in equilibrium with s-cis, copolymerization still competes with cycloaddition.The s-trans-locked verbenene forms only copolymer, while s-cis-locked cyclopentadiene and 1,2-dimethylenecyclopentane form only cycloadduct rapidly.Our explanation involves a 2-hexene-1,6-diradical, formed by combination between the terminal carbons of the s-gauche or s-trans diene and acrylonitrile.This does not cyclize but initiates copolymerization.Competitively s-cis conformer undergoes classical concerted addition.
216. Bicyclooctanes. Syntheses and Hydrolyses of 6-exo-substituted 2-exo- and 2-endo-Bicyclooctyl p-Toluenesulfonates. Part 9
Grob, Cyril A.,Sawlewicz, Pawel
, p. 1859 - 1867 (2007/10/02)
The synthesis of the title compounds and their hydrolysis products in 70percent dioxane are described.
222. Inductivity and Bridging in 2-Bicyclooctyl Cations. Polar Effects, Part II.
Grob, Cyril A.,Sawlewicz, Pawel
, p. 1906 - 1917 (2007/10/02)
The solvolysis rates and products of several 6-substituted 2-exo- and 2-endo-bicyclooctyl p-toluenesulfonates, 12 and 13, respectively, are reported.Inductivity, as measured by the reaction constants pI, is considerably less in the exo-series 12 (pI = -1.50) than in the corresponding 2-exo-norbornyl p-toluenesulfonates 1 (pI = -2.0).It is proposed that, for geometrical reasons, bridging of the cationic center C(2) by C(6) is not as strong in the bicyclooctane series 12 as it is in the norbornane series 1.On the other hand, inductivity is higher in the 2-endo-bicyclooctane series 13 (pI = -1.0) than in the corresponding 2-endo-norbornane series 3 (pI = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion.The relative yields of exo- and endo-substitution products from the series 12 and 13, are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations.But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2-endo-bicyclooctane series 13.Consequently, in the free unsubstituted bicyclooctane cation C(2) is bridged symmetrically by C(6) and C(7), in contrast to the current concept of 'non-classical' two-electron-three-center bonding.
