Intramolecular and intermolecular kinetic isotope effects (KIE) in the nitrosoarene ene reaction: Experimental evidence for reversible intermediate formation
Intramolecular and intermolecular kinetic isotope effects (KIE) in the nitrosoarene ene reaction: Experimental evidence for reversible intermediate formation
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DOI：
10.1021/jo0266240
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发表时间：
2003-03-21
影响因子：
3.6
通讯作者：
Vougioukalakis, GC
中科院分区：
文献类型：
--
作者：
Adam, W;Krebs, O;Vougioukalakis, GC
研究了氘立体标记的2，3-二甲基-2-丁烯（TME）与亚硝基芳烃烯反应的分子内和分子间动力学同位素效应（KIE）。tract-TME-d（6）（k（H）/k（D）= 3.0）和gem-TME-d（6）（k（H）/k（D）= 4.0）显示出较大的分子内原生同位素效应。相反，顺式-TME-d（6）中的分子内竞争（k（H）/k（D）= 1.5）和TME-d（0）/TME-d（12）对的分子间竞争（k（H）/k（D）= 1.98）显示出相当小的、但机械上显著的动力学同位素效应。后一个事实是合理的，在可逆形成的三元环中间体，即氮丙啶N-氧化物，或类似的不对称，极化的双自由基在第一步的反应。这种可逆性也已经暗示了较早的三唑啉二酮（ArNO）和单线态氧（O-1（2））与氘立体标记的2-丁烯，但三个亲烯体，ArNO是最敏感的可逆性，这是由于其温和的反应性和高的空间需求。
The intramolecular and intermolecular kinetic isotope effects (KIE) have been determined for the nitrosoarene ene reaction with deuterium-stereolabeled 2,3-dimethyl-2-butenes (TME). tracts-TME-d(6) (k(H)/k(D) = 3.0) and gem-TME-d(6) (k(H)/k(D) = 4.0) show large intramolecular primary isotope effects. In contrast, the intramolecular competition in cis-TME-d(6) (k(H)/k(D) = 1.5) and the intermolecular competition for the TME-d(0)/TME-d(12) pair (k(H)/k(D) = 1.98) show considerably smaller, but mechanistically significant kinetic isotope effects. The latter fact is rationalized in terms of reversible formation of a three-membered-ring intermediate, namely the aziridine N-oxide, or a similar unsymmetrical, polarized diradical in the first step of the reaction. Such reversibility has also been implied earlier for triazolinedione (TAD) and singlet oxygen (O-1(2)) with deuterium-stereolabeled 2-butenes, but of the three enophiles, ArNO is the most sensitive toward reversibility, which is due to its moderate reactivity and its high steric demand.