Levandowski Brian J, Abularrage Nile S, Raines Ronald T
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States.
J Phys Org Chem. 2023 Apr;36(4). doi: 10.1002/poc.4478. Epub 2022 Dec 13.
The Diels-Alder reactivity of 5-membered dienes is tunable through spirocyclization at the saturated center. As the size of the spirocycle decreases, the Diels-Alder reactivity increases with the cyclobutane spirocycle, spiro[3.4]octa-5,7-diene, being the most reactive. Density functional theory calculations suggest that spiro[3.4]octa-5,7-diene dimerizes 220,000-fold faster than 5,5-dimethylcyclopentadiene and undergoes a Diels-Alder reaction with ethylene 1,200-fold faster than 5,5-dimethylcyclopentadiene. These findings show that spirocyclization is an effective way to enhance the Diels-Alder reactivity of geminally substituted 5-membered dienes.
五元二烯的狄尔斯-阿尔德反应活性可通过饱和中心的螺环化作用进行调节。随着螺环尺寸减小，狄尔斯-阿尔德反应活性增加，其中环丁烷螺环的螺[3.4]辛-5,7-二烯反应活性最高。密度泛函理论计算表明，螺[3.4]辛-5,7-二烯二聚化的速度比5,5-二甲基环戊二烯快220,000倍，与乙烯发生狄尔斯-阿尔德反应的速度比5,5-二甲基环戊二烯快1200倍。这些发现表明，螺环化是增强偕二取代五元二烯狄尔斯-阿尔德反应活性的有效方法。
