Aromatic nitrogen bridgehead compounds. I. The dipyrido[1,2-c:2',1'-e]-imidazolium and related cations

The preparation of the dipyrido[l,2-c:2?,1?-e]imidazolium cation (I) and some substituted cations from 2,2'-bipyridyls and gem-dihalides is described. As expected, (I) exhibits reactions typical for both a-electron excessive and n-electron deficient aromatic ring systems. Thus, (I) may be brominated, methylated, benzoylated, and acetylated at the 6-position; the cation (I) also adds to methyl vinyl ketone. The action of hydroxyl ions in the presence of air produces the corresponding 2,2'-bipyridyls, as does the action of light and air. The rate of bromination of the 6-phenyl derivative (XII) to give the 2,10-dibromo cation (XVI) is comparable to that of naphthalene. The 6-acyl derivatives (XIX) are converted to the parent cation (I) by the action of either acid or base.