Competing Thermal Electrocyclic Ring-Closure Reactions of (2<i>Z</i>)-Hexa-2,4,5-trienals and Their Schiff Bases. Structural, Kinetic, and Computational Studies
作者:José A. Souto、Martín Pérez、Carlos Silva López、Rosana Álvarez、Alicia Torrado、Angel R. de Lera
DOI:10.1021/jo100558p
日期:2010.7.2
substituents of moderate size at C6. The reaction rates were indirectly derived from the empirical observations using a global optimization study based on differential evolution. The cyclizations are torquoselective, and the kinetically favored (E)-alkylidene heterocycles evolve by electrocyclic ring opening/ring closure toward the thermodynamic Z isomers upon extended reaction times. Density functional theory
(2 Z)-六-2,4,5-三烯醛(乙烯基烯醛)与亚烷基-2 H-吡喃和相应的席夫碱衍生物与亚烷基吡啶的电环闭合反应可以同时进行。加入正丁胺后乙烯基烯醛环化和亚胺形成的速率决定了竞争的程度。一系列6-取代的-(2 Z)-4-叔丁基-3-甲基六甲基-2,4,5-三烯醛2和三亚胺4的电环化的活化能取决于C6上取代基之间的空间相互作用和在C4的叔丁基。亚烷基-2 H-吡喃的混合物得到3和3的亚烷基吡啶5,而在C6具有大的基团,而仅后者具有C6- t- Bu,仅前者在C6具有中等大小的取代基。使用基于差异演化的全局优化研究,可从经验观察值间接得出反应速率。环化是热选择性的,并且动力学上有利的(E)-亚烷基杂环是通过电环开/闭向热力学Z演化而来的反应时间延长的异构体。电环化的密度泛函理论(DFT)计算有助于将其表征为具有伪周环特征的单旋转过程,并使合理化反应性趋势和扭转选择性成为可能。