Department of Chemistry and Biochemistry , University of California, Los Angeles , Los Angeles , California 90095 , United States.
Institute of Applied Synthetic Chemistry , TU Wien , 1110 Vienna , Austria.
J Am Chem Soc. 2019 Feb 13;141(6):2224-2227. doi: 10.1021/jacs.8b13088. Epub 2019 Jan 31.
We have investigated the inverse electron-demand Diels-Alder reactions of trans-cyclooctene (TCO) and endo-bicyclo[6.1.0]nonyne (BCN) with a 1,2,4,5-tetrazine, a cyclopentadienone, and an ortho-benzoquinone. Tetrazines react significantly faster with TCO compared to BCN because the highest occupied molecular orbital (HOMO) of TCO is significantly higher in energy than the HOMO of BCN and there is less distortion of the tetrazine. Despite the different HOMO energies, TCO and BCN have similar reactivities toward cyclopentadienones, while BCN is significantly more reactive than TCO in the cycloaddition with ortho-benzoquinone. We find that the higher reactivity of BCN compared to TCO with ortho-benzoquinone is due to secondary orbital interactions of the BCN HOMO-1 with the diene LUMO.
我们研究了反电子需求 Diels-Alder 反应中环辛烯（TCO）和endo-双环[6.1.0]壬炔（BCN）与 1,2,4,5-四嗪、环戊二烯酮和邻苯醌的反应。四嗪与 TCO 的反应速度明显快于 BCN，因为 TCO 的最高占据分子轨道（HOMO）的能量明显高于 BCN 的 HOMO，并且四嗪的变形较小。尽管 HOMO 能量不同，但 TCO 和 BCN 对环戊二烯酮的反应活性相似，而 BCN 与邻苯醌的环加成反应活性明显高于 TCO。我们发现，与邻苯醌相比，BCN 与 TCO 的反应活性更高，这是由于 BCN HOMO-1 与二烯 LUMO 的次级轨道相互作用所致。
