Synthesis of biphenylenes and tetraphenylenes using copper-catalyzed coupling of arylzinc intermediates

Biphenylene and some of its 2,3,6,7- and 1,8-substituted derivatives were s ynthesized using the CuCl2-mediated intramolecular coupling of an organozin c species prepared from 2,2'-dilithiobiaryls with one or two molar equiv. o f ZnCl2 or ZnBr2 in THF. Although most of the reactions of 2,2'-dilithiobia ryls with CuCl2 in THF in the absence of ZnCl2 or ZnBr2 led to biphenylenes as a major product, similar reactions of the organozinc species with CuCl2 in THF produced biphenylenes in much better yields, due to smooth transmet allation and reductive elimination reactions. In particular, the copper-med iated cyclization of benzannelated organozinc intermediates, prepared from equimolar proportions of 2,2'-dilithiobiaryls with ZnCl2, proceeded smoothl y and selectively to afford the desired biphenylenes in 46-81% yield except for the reaction of the zinc intermediate derived from 4,4',5,5'-tetrameth oxy-2,2'-dilithiobiphenyl with ZnCl2 (1.0 molar equiv.). The reaction of th e tetramethoxy-substituted organozinc species with CuCl2 produced 2,3,6,7,1 0,11,14,15-octamethoxytetraphenylene as a major product in 67% yield.