Efficient Construction of Biaryls and Macrocyclic Cyclophanes via Electron-Transfer Oxidation of Lipshutz Cuprates
| Autor: | Mo Wu, Yoshihiro Miyake, Yoshiyuki Kuwatani, M. Jalilur Rahman, Masahiko Iyoda |
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| Rok vydání: | 2006 |
| Předmět: | |
| Zdroj: | The Journal of Organic Chemistry. 71:6110-6117 |
| ISSN: | 1520-6904 0022-3263 |
| Popis: | An efficient method for the homocoupling of aryl halides by electron-transfer oxidation of Lipshutz cuprates (Ar2Cu(CN)Li2) 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 D2-symmetric structure with a twisted rhombic arrangement of four thiophene rings, whereas the methylene- and oxygen-bridged cyclophanes 5b and 5c possess C2h- and C2-symmetric structures with chair- and boatlike conformations, respectively. The 1H NMR spectrum of C2-symmetric 5c is temperature-dependent, and the activation energy (DeltaG) for the conformational change is 10.1 kcal/mol. |
| Databáze: | OpenAIRE |
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