Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, United States.
J Org Chem. 2011 Oct 7;76(19):7994-8002. doi: 10.1021/jo201606z. Epub 2011 Sep 13.
The effects of furan and maleimide substitution on the dynamic reversibility of their Diels-Alder reactivity have been investigated computationally and by (1)H NMR spectroscopy. Furan and furan derivatives bearing methoxy, methyl, or formyl groups at their 2- or 3-positions were investigated with maleimide and maleimide derivatives bearing N-methyl, N-allyl, and N-phenyl substituents. Computational predictions indicate that electronic and regiochemical effects of furan substitution significantly influence their Diels-Alder reactivity with maleimide, with reaction free energies of exo adduct formation ranging from ΔG = -9.4 to 0.9 kcal/mol and transition state barriers to exo adduct formation ranging from ΔG(‡) = 18.9 to 25.6 kcal/mol. Much less variation was observed for the reactivity of N-substituted maleimide derivatives and furan, with reaction and transition state free energies each falling within a range of 1.1 kcal/mol. Dynamic exchange experiments monitored by (1)H NMR spectroscopy support computational predictions. The results indicate the reactivity and reversibility of furan-maleimide cycloadditions can be tuned significantly through the addition of appropriate substituents and have implications in the use of furan and maleimide derivatives in the construction of thermally responsive organic materials.
通过计算和（1）H NMR 光谱研究了呋喃和马来酰亚胺取代对其 Diels-Alder 反应动态可逆性的影响。研究了在 2-或 3-位带有甲氧基、甲基或甲酰基的呋喃及其衍生物与带有 N-甲基、N-烯丙基和 N-苯基取代基的马来酰亚胺及其衍生物的反应性。计算预测表明，呋喃取代的电子和区域化学效应显著影响其与马来酰亚胺的 Diels-Alder 反应性，外加成物形成的反应自由能范围为 ΔG = -9.4 至 0.9 kcal/mol，外加成物形成的过渡态能垒范围为 ΔG(‡) = 18.9 至 25.6 kcal/mol。N-取代马来酰亚胺衍生物和呋喃的反应性变化较小，反应和过渡态自由能均在 1.1 kcal/mol 的范围内。（1）H NMR 光谱监测的动态交换实验支持计算预测。结果表明，通过添加适当的取代基，可以显著调节呋喃-马来酰亚胺环加成的反应性和可逆性，这对在热响应有机材料的构建中使用呋喃和马来酰亚胺衍生物具有重要意义。
