Utility and Synthetic Uses of Mannich Reaction: An Efficient Route for Synthesis of Thiadiazino‐[1,3,5][3,2‐a]benzimidazoles

Abstract

Abstract 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. Keywords: Double Mannich reactionsynthesiscyclizationthiadiazines