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

Abstract

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 [Ar 2 Cu(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 À Cu À 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,

Conjugated Macrocycles: Concepts and Applications

“…There are three reported systems 3 a-f, 4 a-f, and 5 concerning the ring current effect of macrocyclic annulenes. [13][14][15] Interestingly, [34]annulene 4 c is aromatic, whereas [38]annulene 4 d does not show any aromatic ring current effects. In contrast, [28]annulene 4 e is paratropic, whereas [32]annulene 4 f is atropic.…”

“…Iyoda and co-workers have developed a new method for preparing cyclic oligophenylenes by using electron-transfer (ET) oxidation of Lipshutz cuprates (Scheme 7). [38,39] Nonaphenylene 46 a was first synthesized by Meyer and Staab (1969) in very low yield (0.97 %) by the CuCl 2 -mediated coupling of a Grignard derivative of 4,4''-dibromo-o-terphenyl. [40] Fujioka also obtained 46 a in 4.5 % yield as a byproduct in the synthesis of hexaphenylene (16 %) by a CuCl 2 -mediated cross-coupling of the Grignard derivatives of 4,4''-dibromo-o-terphenyl and 2,2''-dibromo-p-terphenyl.…”

“…[38] Although strained cyclophanes are p acids and can be reduced chemically and electrochemically to produce the corresponding radical anions and dianions, [36c] 44 behaves as a p base and forms a CT complex with TCNE (l max = 638 nm) and DDQ (l max = 790 nm) in Transition-metal-mediated coupling of aryl halides is frequently employed for the synthesis of cyclic oligophenylenes. In many cases, however, the target macrocycles can be prepared only in low yields because of the formation of linear oligomers as side products, which require additional separation.…”

Konjugierte Makrocyclen: Konzepte und Anwendungen

“…[38] Obwohl gespannte Cyclophanen pSäuren sind, die chemisch und elektrochemisch zu den entsprechenden Radikalanionen und -dianionen reduziert werden kçnnen, [36c] verhält sich 44 wie eine p-Base und bildet CT-Komplexe mit Tetracyanethylen (TCNE; l max = 638 nm) und 2,3-Dichlor-5,6-dicyanbenzochinon (DDQ; l max = 790 nm) in CH 2 Der ortho-Cyclus 57 und der para-Cyclus 59 bilden ein vollständig konjugiertes System, wohingegen der meta-Cyclus 58 aus kreuzkonjugierten Benzoleinheiten besteht.…”

Zirconacycle-mediated synthesis of carbocycles

“…Xi's group [73,74] reported 1,4-dicopper-1,3-dienes made from dilithio precursors underwent cyclization reactions to afford octasubstituted semibullvalenes [75,76].…”