Some studies with benzimidazoles and related heterocycles

The thesis reports the first examples of Reissert compounds prepared from the benzimidazole ring system; the first examples of monocyclic five-membered ring Reissert compounds; and an exploration of the chemistry of these compounds. The key procedure for their formation utilizes trimethylsilyl cyanide in a single-phase non-aqueous medium. Previous attempts to synthesize five-membered ring Reissert compounds have failed because, under the conventional two-phase conditions, the reaction either does not proceed or ring opening of the heterocycle occurs. The reactions of benzimidazole with an acid chloride (aliphatic, aromatic or chloroformate), trimethylsilyl cyanide and a Lewis acid catalyst in dichloromethane has been shown to give rise to 1,3-bisacyl-2-cyano-2,3-dihydrobenzimidazoles in yields of 69–90%. Eight such novel Reissert compounds have been prepared and have been shown to be versatile in the modification of the heterocyclic ring system. Analogous reactions with N-alkylbenzimidazoles did not give Reissert compounds: use of aroyl chlorides gave only aroyl cyanides; use of chloroformates unexpectedly provided a new direct route to 2-cyanobenzimidazoles. [Continues.]