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Title: Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate

Abstract

The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.

Authors:
; ; ;
Publication Date:
Research Org.:
Univ. of Tennessee, Knoxville (USA)
OSTI Identifier:
7148548
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Am. Chem. Soc.; (United States); Journal Volume: 110:6
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CYCLOALKENES; CHEMICAL PREPARATION; DIENES; DEHYDROCYCLIZATION; CATIONS; ELECTRON SPIN RESONANCE; EXPERIMENTAL DATA; RADICALS; REACTION INTERMEDIATES; ALKENES; CHARGED PARTICLES; CHEMICAL REACTIONS; DATA; HYDROCARBONS; INFORMATION; IONS; MAGNETIC RESONANCE; NUMERICAL DATA; ORGANIC COMPOUNDS; POLYENES; RESONANCE; SYNTHESIS; 400201* - Chemical & Physicochemical Properties

Citation Formats

Guo, Q.X., Qin, X.Z., Wang, J.T., and Williams, F. Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate. United States: N. p., 1988. Web. doi:10.1021/ja00214a057.
Guo, Q.X., Qin, X.Z., Wang, J.T., & Williams, F. Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate. United States. doi:10.1021/ja00214a057.
Guo, Q.X., Qin, X.Z., Wang, J.T., and Williams, F. Wed . "Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate". United States. doi:10.1021/ja00214a057.
@article{osti_7148548,
title = {Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate},
author = {Guo, Q.X. and Qin, X.Z. and Wang, J.T. and Williams, F.},
abstractNote = {The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.},
doi = {10.1021/ja00214a057},
journal = {J. Am. Chem. Soc.; (United States)},
number = ,
volume = 110:6,
place = {United States},
year = {Wed Mar 16 00:00:00 EST 1988},
month = {Wed Mar 16 00:00:00 EST 1988}
}
  • Cyclooctatetraene (1) is well-known to have a tub-shaped (D{sub 2d}) geometry with alternating double bonds, and its radical cation (1{sup {sm bullet}+}) evidently also possesses a nonaromatic and nonplanar structure. Here the authors describe a novel photoisomerization in which 1{sup {sm bullet}+} undergoes homoaromatization by 1,5-closure to yield the bridged 1,4-bishomobenzene (bicyclo(3.3.0)octa-2,6-diene-4,8-diyl) radical cation 2{sup {sm bullet}+} at temperatures as low as 80 K, a symmetry-allowed reaction in which the excited state of 1{sup {sm bullet}+} correlates adiabatically with the ground state of 2{sup {sm bullet}+}. This photoisomerization is responsible for the previously reported photochromic effect in this system.
  • The chemistry of neutral 1,5-hexadiene (1) has been studied extensively. It undergoes the well-known (degenerate) Cope rearrangement under thermal conditions. Facile transformations occur upon irradiation, and depending on the photochemical conditions allylcyclopropane and bicyclo(2.1.1)- and (2.2.0)hexane may be formed. Isotopic separation of deuterated 1 in favor of deuterium situated in the external vinyl sites has been demonstrated with infrared laser; deuterium in the allylic positions, however, is favored under thermal conditions. In contrast, recent electron impact studies xDdicate a chemical inertness of the radical cation of 1 (1/sup +/.). It was shown by photodissociation spectroscopy that 1/sup +/in equilibrium remainsmore » as an unconjugated diene at low internal energies. Comparison of the heat of formation of C/sub 5/H/sub 7//sup +/ions formed by CH/sub 3/. loss from isomeric C/sub 6/H/sub 10/ radical cations (ions of m/z 67 give rise to base peak in the normal mass spectra of C/sub 6/H/sub 10/ isomers) and the kinetic energy release (T) associated therewith showed that 1/sup +/in equilibrium among its linear isomers forms the cyclopentenyl cation with the lowest excess energy and smallest T value. This result is in accord with the photodissociation results insofar as 1/sup +/in equilibrium among its linear isomers forms the cyclopentenyl cation with the lowest excess energy and smallest T value. This result is in accord with the photodissociation results insofar as 1/sup +/in equilibrium cannot isomerize to another linear diene prior to decomposition. The collisional activation mass spectra of C/sub 6/H/sub 10/ isomers confirmed that nondecomposing 1/sup +/in equilibrium has no or only little resemblance with the radical cations of 1,3-, 1,4-, and 2,4- hexadiene, cyclohexene, and 1-methylcyclopentene. In light of the apparent retention of structure of 1/sup +/in equilibrium, this work is concerned with how the cyclopentenyl cation is formed.« less
  • The electronic structure and the interconversion of the radical cations of the (CH){sub 8} group have recently attracted attention. Among the (CH){sub 8} hydrocarbons, cubane has high symmetry (O{sub h}) and the highest strain energy. Its physicochemical properties continue to attract experimental and theoretical interest. The cubane radical cation (1) was first studied in neon matrices at 4 K. Here we report isomerization of 1 to the bridged 1,4-bishomobenzene radical cation (2), which was first demonstrated to be formed by the ring-opening of the semibullvalence radical cation. We show here that radiolytic oxidation of cuneane also yields 2.
  • The remarkable fact that semibullvalene (1) undergoes a rapid degenerate Cope rearrangement on the NMR time scale at {minus}150{degree}C has prompted efforts to lower the activation energy of only 4.8 kcal mol{sup {minus}1} for the parent molecule to a negative value by appropriate substitution. This exciting goal where the expected 1,4-bishomobenzene transition structure would be stabilized relative to the localized semibullvalene structures has not hitherto been realized, however, even for purposely designed derivatives. In contrast, they now report that radiolytic oxidation of 1 in Freon matrices generates the delocalized bicyclo(3.3.0)octa-2,6-diene-4,8-diyl radical cation 2{sup {sm bullet}+} as a stable species.