Oxidative reactions of polyarylpyrroles. Part 3. Oxidative trimerization of 2,5-diphenylpyrrole

Abstract

As in the oxidative reaction of 2,3,5-triphenylpyrrole previously studied, the oxidation of 2,5-diphenylpyrrole with potassium dichromate gave the dimer 2,2′,5,5′-tetraphenyl-3,3′-bipyrrole (2) and the related hydroxy-derivative 3-(2,5-diphenylpyrrol-3-yl)-2,5-diphenyl-2H-pyrrol-2-ol (6), together with the tetracyclic compound 1,6a-dihydro-2,5,6a-triphenylbenzo[g]pyrrolo[3.2-e]indole (3), whose formation involves the α-position of the pyrrole nucleus and the α′-phenyl group of the other pyrrole ring. In addition, large amounts of both the trimer 2,3-bis-(2,5-diphenylpyrrol-3-yl)-2,5-diphenyl-2H-pyrrole (4) and the tetracyclic compound 6a,6b-dihydro-1,3,5,6a,6b,8-hexaphenyl-2H-benzo[1,2-c:4,3-b′:5,6-b″]tripyrrole (5) were obtained. The formation of the various products of the oxidation is demonstrated in terms of the intermediate (2).