Tellurium-Mediated Halogen Transfer from Polyhaloalkanes to Diyne Acceptors
摘要:
Elemental tellurium catalyzes transfer of halogen from (CHCl2)(2), from C2HCl5 and from (CHBr2)(2), to the phenylated diynes 1-3, 17, 20, and 24, in which the alkyne moieties are in close proximity. The process is associated with cyclorearrangement reactions by which halogenated polycycles are formed. In boiling C2HCl5, derivatives of 1,2-bis(phenylethynyl)benzenes afford 5-halogenated indeno[2,1-a]indenes, 1,8-bis(phenylethynyl)naphthalene gives a chlorinated benzo[k]fluoranthene derivative, and 2,2'-bis(phenylethynyl)[1,1'-biphenyl] forms 9-chloro-14-phenylbenz[a,c]anthracene. Diynes 25 and 26 in which the ethynyl functions are further removed from each other fail to yield halogenated products. Diyne 25 undergoes oxidative cyclization by which 1,3-diphenyldibenzo[3,4:6,7]cyclohepta[1,2-c]furan (29) is formed. Compound 26 is transformed to hydrocarbon 32, which involves a phenyl ring walk and elimination of H2Te.
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
Cu-Catalyzed oxidative 1 : 2 couplings of arynes with nucleophilic terminalalkynesunderaerobicconditions are described herein. A mechanistic investigation revealed a plausible involvement of an aryl-Cu(III)-generating pathway. By this method, ubiquitous arenediynes can be efficiently assembled in a single step under mild conditions.