Leach Andrew G, Houk K N, Foote Christopher S
AstraZeneca Pharmaceuticals, Mereside, Alderley Park, Macclesfield, Cheshire, UK.
J Org Chem. 2008 Nov 7;73(21):8511-9. doi: 10.1021/jo8016154. Epub 2008 Oct 4.
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.
采用B3LYP/6-31G* 和CASMP2计算方法研究了单线态氧与反式环辛烯的烯反应。这些方法预测该反应涉及一个过氧环氧化物中间体，而对于诸如四甲基乙烯等烯烃，相同方法预测其反应通过两步无中间体机理进行，不存在过氧环氧化物中间体。机理的变化是因为反式环辛烯在氢提取的过渡态中施加了相当大的张力。过氧环氧化物是通过一个极化双自由基中间体形成的，这可能导致烯烃异构化的观察结果。由于提取的势垒，极化双自由基也成为一个极小值。
