Utility and synthetic uses of Mannich reaction: An efficient route for synthesis of thiadiazino-[1,3,5][3,2-a]benzimidazoles

The utilities of the Mannich reaction in synthetic organic chemistry are reviewed. The behaviors of Mannich reactions on several bifunctional heterocyclic compounds have been reported. A new class of heterocyclic compounds, thiadiazino[1,3,5][3,2-a]benzimidazoles 12a-g, were obtained by reaction of 2-mercaptobenzimidazole with primary aliphatic amines in a one-step synthesis. An attempt to apply this reaction using primary aromatic amines lead to the formation of the well-known Mannich bases 11a-g rather than the N -substituted thiadiazines 13.