Copper-Mediated Aryl-Aryl Couplings for the Construction of Oligophenylenes and Related Heteroaromatics

Efficient methods for the syntheses of biaryls by the copper-mediated homocoupling of arylmetals are summarized. First, a smooth transmetallation between arylzinc halides and copper(II) salts has been employed for the selective homocoupling of arylzinc halides to produce either biphenylenes or tetraphenylenes. This reaction has been applied to the synthesis of cyclic oligothiophenes. Second, an efficient method for the homocoupling of aryl halides by the electron-transfer (ET) oxidation of Lipshutz cuprates [Ar2Cu(CN)Li-2] with organic electron acceptors has been developed. The ET oxidation of cuprates with 1,4-benzoquinones proceeds smoothly to afford the corresponding coupling products in moderate to high yields. The ET oxidation of cuprates has been applied to the synthesis of either thiophene- or benzene-fused 10-membered ring cyclophanes. For the synthesis of macrocyclic cyclophanes, a linear C-Cu-C structure of Lipshutz cuprates should be maintained in the dimetallacyclic intermediates to efficiently produce large-ring cyclophanes. Moreover, nonaphenylenes and dodecaphenylenes have been synthesized using the ET oxidation of cuprates with duroquinone. Interestingly, hexadodecyloxynonaphenylene exhibits different nanostructures between fibrous materials in solution and cast films on a surface. Films of this compound can detect vaporized nitroaromatics such as dinitrobenzene and trinitrobenzene.