Approaches to heterocyclic analogues of biphenylene. Part II. Some 5,5′6,6′-tetraphenyl-2,2′-bipyrazinyls

Abstract

Treatment of appropriate halogenodiphenylpyrazines with copper in dimethylformamide gives 5,5′,6,6′-tetraphenyl-2,2′-bipyrazinyl and some 3,3′-disubstituted derivatives. The latter were converted into further disubstituted tetraphenylbipyrazinyls, but a 3,3′-dihalogeno-derivative, a possible precursor of 2,3,6,7-tetraphenyl-1,4,5,8-tetraazabiphenylene, could not be obtained. I.r. spectra suggest that hydroxypyrazines exist predominantly in the ‘amide’ structure, but 3,3′-dihydroxy-5,5′,6,6′-tetraphenylbipyrazinyl exists only in the hydroxy-form, which is stabilised by hydrogen-bonding. Methoxycarbonyl groups in methyl 3-hydroxy- or 3-methoxy-5,6-diphenylpyrazine-2-carboxylates, but not in methyl 3-chloro-5,6-diphenylpyrazine-2-carboxylate, are converted into carboxy-groups on treatment with copper(I) chloride in hot dimethylformamide; the ester groups in dimethyl 5,5′,6,6′-tetraphenylbipyrazinyl-3,3′-dicarboxylate undergo similar cleavage.