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.
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.
Selectivity of cyano-Gilman cuprates: synthesis of 10-membered ring cyclophanes
作者:S. M. Humayun Kabir、Masahiko Iyoda
DOI:10.1039/b008102g
日期:——
The oxidation of cyano-Gilman cuprates, derived from dibromodithienyl sulfide, dibromodithienyldimethylsilane and dibromodithienylmethane, with molecular oxygen furnishes 10-memberedring cyclophanes selectively and an X-ray analysis of cyclophane 9 reveals that it possesses an anti conformation.
氰基-吉尔曼铜酸盐(衍生自二溴二噻吩基硫化物、二溴二噻吩基二甲基硅烷和二溴二噻吩基甲烷)与分子氧的氧化选择性地提供了 10 元环环烷,环烷 9 的 X 射线分析表明它具有反构象。
Synthesis of dithienothiophenes, cyclopentadithiophene and silacyclopentadithiophenes using palladium-catalyzed cyclization
作者:Masahiko Iyoda、Mami Miura、Shigeru Sasaki、S.M.Humayun Kabir、Yoshiyuki Kuwatani、Masato Yoshida
DOI:10.1016/s0040-4039(97)00979-9
日期:1997.6
The intramolecular cyclization of bromothiophene derivatives with hexamethylditin in the presence of tetrakis(triphenylphosphine)palladium(0) gave dithienothiophenes, cyclopentadithiophene, and silacyclopentadithiophenes in moderate to good yields.