Department of Chemistry, West Chester University of Pennsylvania , West Chester, Pennsylvania 19383, United States.
J Org Chem. 2017 Feb 3;82(3):1301-1315. doi: 10.1021/acs.joc.6b02025. Epub 2017 Jan 19.
In this Article, we present a new method for the synthesis of diarylnorbornadiene derivatives. Through the use of a two-step procedure consisting of a tandem alkene insertion-Suzuki coupling reaction followed by a DDQ dehydrogenation, we have been able to synthesize derivatives with a wide variety of substituents. We also present the results of UV-visible spectroscopy studies and kinetics experiments that show the effect of substituent on light absorption properties of the norbornadienes as well as the kinetic stability of the quadricyclanes that result from their photochemical conversion. While substitution on the aromatic rings had comparatively little effect on quadricyclane lability, substitution at a bridgehead position with a methyl group produced a quadricyclane that thermally reverted to the norbornadiene at a rate that was significantly slower than that for the quadricyclane without the methyl substituent. From the results of the kinetics experiments, we determined that the reversion of the quadricyclanes occurs via a free radical mechanism with very little contribution from polar effects. This observation led us to speculate as to whether our data may form the basis for a free radical substituent constant, σ•, analogous to the traditional Hammett σ parameter.
在这篇文章中，我们提出了一种合成二芳基降冰片二烯衍生物的新方法。通过使用包括串联烯烃插入-Suzuki 偶联反应和 DDQ 脱氢反应的两步法，我们已经能够合成具有各种取代基的衍生物。我们还介绍了紫外可见光谱研究和动力学实验的结果，这些结果表明取代基对降冰片二烯光吸收性质以及其光化学转化产生的双环[2.2.1]庚烷的动力学稳定性的影响。虽然芳环上的取代对双环[2.2.1]庚烷的不稳定性影响相对较小，但在桥头位置用甲基取代会产生一种双环[2.2.1]庚烷，其热回环至降冰片二烯的速率明显慢于没有甲基取代的双环[2.2.1]庚烷。根据动力学实验的结果，我们确定双环[2.2.1]庚烷的反转是通过自由基机制进行的，极性效应的贡献很小。这一观察结果促使我们推测，我们的数据是否可以作为类似于传统的 Hammett σ 参数的自由基取代常数 σ•的基础。
