14926-88-6Relevant articles and documents
Thermal reactions of 8-methylbicyclo[4.2.0]oct-2-enes: Competitive diradical-mediated [1,3] sigmatropic, stereomutation, and fragmentation processes
Bogle, Xavier S.,Leber, Phyllis A.,McCullough, Lynne A.,Powers, David C.
, p. 8913 - 8918 (2007/10/03)
At 275 °C, 8-exo-methylbicyclo[4.2.0]oct-2-ene (1a) undergoes a [1,3] sigmatropic rearrangement to 5-methylbicyclo[2.2.2]oct-2-enes, of which the orbital symmetry-allowed si product is only marginally favored over the forbidden sr product; that is, silsr is 2.4. Accompanying the [1,3] shift are significant amounts of epimerization and fragmentation. The 8-endo epimer 1b, which yields no [1,3] product, experiences primarily direct fragmentation and secondarily epimerization. A diradical intermediate can account for all such observations.
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.
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.
