Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.
Angew Chem Int Ed Engl. 2016 Jul 11;55(29):8266-9. doi: 10.1002/anie.201601989. Epub 2016 May 4.
It is known that the fluoro group has only a small effect on the rates of electrophilic aromatic substitutions. Imagine instead a carbon-fluorine (C-F) bond positioned tightly over the π cloud of an aryl ring-such an orthogonal, noncovalent arrangement could instead stabilize a positively charged arene intermediate or transition state, giving rise to novel electrophilic aromatic substitution chemistry. Herein, we report the synthesis and study of molecule 1, containing a rigid C-F⋅⋅⋅Ar interaction that plays a prominent role in both its reaction chemistry and spectroscopy. For example, we established that the C-F⋅⋅⋅Ar interaction can bring about a >1500 fold increase in the relative rate of an aromatic nitration reaction, affording functionalization on the activated ring exclusively. Overall, these results establish fluoro as a through-space directing/activating group that complements the traditional role of fluorine as a slightly deactivating aryl substituent in nitrations.
已知氟基团对亲电芳香取代反应的速率只有很小的影响。相反，设想一个氟碳（C-F）键紧密地位于芳环的π云上方——这种正交的非共价排列可以稳定带正电荷的芳烃中间体或过渡态，从而产生新的亲电芳香取代反应化学。在这里，我们报告了分子 1 的合成和研究，该分子含有刚性的 C-F⋅⋅⋅Ar 相互作用，在其反应化学和光谱学中都起着重要作用。例如，我们确定 C-F⋅⋅⋅Ar 相互作用可以使芳香硝化反应的相对速率提高 1500 倍以上，仅在活化环上进行官能化。总的来说，这些结果确立了氟作为一种空间传递/激活基团，补充了氟作为硝化反应中略微失活的芳基取代基的传统作用。
