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 pseudohalogen es (cyanide, azide), carbon and heterocyclic N-nucleophiles in the presence of manganese dioxide to give the corresponding substituted azaisobenzimida zoles (= 2H-azabenzimidazoles) 4, 8, 23-26 and 29-33, 36 or dihydroazabenzi midazoies (= 2,3-dihydro-1H-azabenzimidazoles 7, 22, 34 and 35. In 8 one of the two imidazolyl-substituents can be replaced by nucleophiles yielding t he compounds 9-15. Treatment of 6'-bromo-2,3-dihydro-4-azabenzimidatele 16 with morpholine or piperidine results in loss of the Br-atom presumably by an AE(a)-mechanism. Reduction of the substituted azaisobenzimidazoles with sodium hydrosulfite followed by fission of the cyclohexane ring leads to su bstituted o-diaminopyridines. They were cyclised in situ with various conde nsing agents to give new heterocyclic systems. Equimolar mixtures of some a zaisobenzimidazoles and dihydroazabenzimidazoles lead to the formation of c oloured charge transfer complexes stable only in the solid state. Owing to poor electron-acceptor properties the complex dissociates in solution.