Reactions of 2,3-dihydrospiro[1H-4- and 5-azabenzimidazole-2,1′-cyclohexane] with nucleophiles: A potential route to some substituted aromatic heterocycles

The readily available title compounds 2, 16 and 27 react with pseudohalogenes (cyanide, azide), carbon and heterocyclic N‐nucleophiles in the presence of manganese dioxide to give the corresponding substituted azaisobenzimidazoles (= 2H‐azabenzimidazoles) 4, 8, 23–26 and 29–33, 36 or dihydroazabenzimidazoles (= 2,3‐dihydro‐1H‐azabenzimidazoles 7, 22, 34 and 35. In 8 one of the two imidazolyl‐substituents can be replaced by nucleophiles yielding the compounds 9–15. Treatment of 6′‐bromo‐2,3‐dihydro‐4‐azabenzimidazole 16 with morpholine or piperidine results in loss of the Br‐atom presumably by an AEa‐mechanism. Reduction of the substituted azaisobenzimidazoles with sodium hydrosulfite followed by fission of the cyclohexane ring leads to substituted o‐diaminopyridines. They were cyclised in situ with various condens ing agents to give new heterocyclic systems. Equimolar mixtures of some azaisobenzimidazoles and dihydroazabenzimidazoles lead to the formation of coloured charge transfer complexes stable only in the solid state. Owing to poor electron‐acceptor properties the complex dissociates in solution.