Theoretical prediction of a perepoxide intermediate for the reaction of singlet oxygen with trans-cyclooctene contrasts with the two-step no-intermediate ene reaction for acyclic alkenes.
B3LYP/6-31G* and CASMP2 calculations have been employed to study the ene reaction of singlet oxygen with trans-cyclooctene. These methods predict that the reaction involves a perepoxide intermediate, whereas alkenes such as tetramethylethylene are predicted by the same methods to occur by a two-step no-intermediate mechanism, with no perepoxide intermediate. The change in mechanism arises because the trans-cyclooctene imposes a substantial strain in the transition state for hydrogen abstraction. The perepoxide is formed through a polarized diradical intermediate that can lead to the observation of alkene isomerization. The polarized diradical also becomes a minimum because of the barrier to abstraction.
Leach
Andrew G
AG
AstraZeneca Pharmaceuticals, Mereside, Alderley Park, Macclesfield, Cheshire, UK.
Houk
K N
KN
Foote
Christopher S
CS
D000475:Alkenes / Q000737:chemistry; D034242:Cyclooctanes / Q000737:chemistry; D004852:Epoxy Compounds / Q000737:chemistry*; D008956:Models, Chemical; D008962:Models, Theoretical; D026082:Singlet Oxygen / Q000737:chemistry*
D000475:Alkenes; D034242:Cyclooctanes; D004852:Epoxy Compounds; D026082:Singlet Oxygen