Classical Versus NonstatisticalBehavior in the C²-C6/EneCyclization of Enyne-Allenes: IntramolecularKinetic Isotope Effects and Radical Clock Reactions
Classical Versus NonstatisticalBehavior in the C²-C6/EneCyclization of Enyne-Allenes: IntramolecularKinetic Isotope Effects and Radical Clock Reactions
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烯炔-联烯的 C²-C6/Ene 环化中的经典与非统计行为：分子内动力学同位素效应和自由基时钟反应
DOI：
10.1055/s-0029-1218799
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
M. Schmittel
中科院分区：
文献类型：
--
作者：
C. Vavilala;J. W. Bats;M. Schmittel
通过原子钟打开和分子内动力学同位素效应研究了芳基对烯丙烯C²-C 6/烯环化机理的影响。只要在炔端或烯端连接一个芳基，热反应就会逐步进行，并显示出显著的非统计动力学效应。尽管如此，我们还是能够利用超快的二苯基环丙基原子钟反应在分子内拦截中间的二自由基。当芳基同时存在于炔端和烯端时，分子内动力学同位素效应符合经典的逐步机制。因此，本研究证明了反应机理从非统计逐步机理向经典逐步行为的转变，这取决于取代基。
The effects of aryl groups on the mechanism of the C ²-C 6/ene cyclization of enyne-allenes were studied by means of radical clock openings and intramolecular kinetic isotope effects. Upon attachment of a single aryl group at either the alkyne or the allene terminus, the thermal reaction proceeds by a stepwise mechanism that shows significant nonstatistical dynamic effects. Despite this, we were able to intercept the intermediate diradical intramolecularly by using the ultrafast diphenylcyclopropyl radical clock reaction. When aryl groups were present at both the alkyne and allene termini, the intramolecular kinetic isotope effects were consistent with a classical stepwise mechanism. The present study thus demonstrates the shift in reaction mechanism from a nonstatistical stepwise mechanism to a classical stepwise behavior, depending on the substituents.