Dimerization of biradicaloid heterocyclic compounds. Nitro derivatives of pyrrolo[1, 2-a]benzimidazole

A new type of easily dimerized heterocyclic compound, viz., nitro derivatives of 2-phenylpyrrolo1,2-a]benzimidazole, was discovered. The reaction proceeds by heating the latter in acetic acid. A radical mechanism for the dimerization that takes into account partial protonation of the starting compound is discussed on the basis of electrochemical data, the high -donor capacity of 2-phenyl-4-methylpyrrolo1,2-a]benzimidazole, the coloration that is characteristic for selfcomplexes, and EPR spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 188–196, February, 1984.