通常,空间正交轨道之间的远程电子通信效率低下,并且仅限于场和感应效应。在这项工作中,我们提供了实验证据,表明可以通过两个简并且相互正交的前沿分子轨道 (MO) 在过渡态的分子内电子转移来实现这种通信。当这些轨道之间的能隙接近零或“轨道交叉”时,正交轨道之间的相互作用被放大。两个空的或两个完全占据的 MO 之间的交叉不会导致稳定,当一个空的 MO 被填充(即电子注入)或填充的 MO 之一被减少(即空穴注入)时,可以“激活” )。在还原环芳构化反应中,这种交叉定义了具有由面内和面外 π 系统定义的能量的过渡态。在此,我们使用轨道交叉在烯二炔的还原性 C1-C5 环芳构化反应中为该概念的实用性提供了实验证据。与类似的自由基环化相比,通过轨道交叉与远程取代基的通信大大提高了闭环步骤的区域选择性。我们还提供了与电子注入苄基化烯二炔的效率有关的光物理数据。与类似的自由基环化相比,通过轨道交叉与远程取代
“Stereoelectronic Umpolung”: Converting a p-Donor into a σ-Acceptor via Electron Injection and a Conformational Change
作者:Paul W. Peterson、Nikolay Shevchenko、Igor V. Alabugin
DOI:10.1021/ol400813d
日期:2013.5.3
efficient hyperconjugative σ-acceptor in reductive cycloaromatization reactions. This apparent reversal of electronic properties is associated with a conformational change that aligns the σ*O–C orbital with the adjacent aromatic system and provides stabilization to the developing negative charge in the TS of the dianionic cyclization of enediynes. The chameleonic character of the OMe group illustrates
A Tandem Catalytic Approach to Methyleneindenes: Mechanistic Insights into <i>gem</i>-Dibromoolefin Reactivity
作者:Christopher S. Bryan、Mark Lautens
DOI:10.1021/ol100844v
日期:2010.6.18
The methylenindene scaffold can be prepared from readily available gem-dibromoolefins using an efficient palladium-catalyzed tandem intermolecular Suzuki/intramolecular Heck reaction. The reaction is highly modular and proceeds under mild conditions. The choice of ligand was found to be crucial to control the selectivity of the reaction. Isolation of intermediates under different conditions provides insight into the mechanism.