Novel electron-transfer oxidation of Lipshutz cuprates with 1,4-benzoquinones: an efficient homo-coupling reaction of aryl halides and its application to the construction of macrocyclic systems
The electron transfer reaction from Lipshutz cuprates, which can be easily prepared from aryl bromides, to 1,4-benzoquinones was found to proceed smoothly, affording either the corresponding homo-coupling products, in modest to excellent yields, or macrocyclic products selectively.
Selectivity of Br/Li Exchange and Deprotonation of 4,4′-Dibromo-3,3′-bithiophene for Synthesis of Symmetrical and Unsymmetrical Dithienoheteroaromatic Rings
作者:Hui Han、Wenling Zhao、Jinsheng Song、Chunli Li、Hua Wang
DOI:10.1021/jo302635y
日期:2013.3.15
synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings (DTHAs) has been developed via intramolecular cyclization of 4,4′-dibromo-3,3′-bithiophene (3). Four reaction conditions including n-BuLi/Et2O, n-BuLi/THF, s-BuLi/Et2O, and t-BuLi/Et2O were employed to react with 3 for selective formation of two types of dicarbanions, which generate the symmetrical and unsymmetrical DTHAs after quenching
通过分子内环化4,4'- dibromo -3,3'-bithiophene(3),开发了对称和不对称的二噻吩杂芳环(DTHA)的新型选择性合成方法。使用包括n -BuLi / Et 2 O,n -BuLi / THF,s -BuLi / Et 2 O和t -BuLi / Et 2 O的四个反应条件与3反应以选择性形成两种类型的二碳双键。生成对称和不对称DTHA具有三个亲电试剂(淬火后小号4A - ç)。提出了DTHAs形成的可能机理。另外,通过X射线单晶分析确认了两个不对称的DTHA。
An efficient method for the homocoupling of aryl halides by electron-transfer oxidation of Lipshutz cuprates (Ar2Cu(CN)Li-2) with organic electron acceptors is disclosed. Thus, various types of Lipshutz cuprates are prepared by successive treatment of aryl or heteroaryl bromides with tert-butyllithium and CuCN. The electron-transfer oxidation of Lipshutz cuprates with p-benzoquinones proceeds smoothly to afford the corresponding homocoupling products in moderate to good yields. Furthermore, it can be applied to the construction of either thiophene- or benzene-fused 10-membered ring cyclophanes. For the synthesis of 10-membered cyclophanes, the linear C-Cu-C structure of Lipshutz cuprates should be maintained in the dimetallacyclic intermediates, producing the large ring cyclophanes efficiently. The X-ray analysis of the cyclophanes reveals that the difference in the bridging atoms results in the different conformations of the macrocyclic rings. Thus, the silicon-bridged cyclophane 5a adopts a D-2-symmetric structure with a twisted rhombic arrangement of four thiophene rings, whereas the methylene- and oxygen-bridged cyclophanes 5b and 5c possess C2h- and C-2-symmetric structures with chair- and boatlike conformations, respectively. The H-1 NMR spectrum of C-2-symmetric 5c is temperature- dependent, and the activation energy (Delta G double dagger) for the conformational change is 10.1 kcal/mol.