One‐Pot Stereoselective Synthesis of Different Fused Multicyclic Iminosugars Based on the Iminium‐Ion Intermediate

Comprehensive Summary Different novel fused multicyclic iminosugars were synthesized from D‐ribose tosylate, aniline and vinyl ethyl ether by one‐pot three‐component stereoselective [4+2] reaction at different temperatures. The iminium‐ion is the key intermediate for the reaction. As a result, several complex fused iminosugars 3a were obtained by aza‐Diels‐Alder mechanism at 60 °C, while a series of aza‐ C ‐glycosides 5a were prepared by Mannich reaction at room temperature accompanied by another tetrahydroquinoline‐fused iminosugars 4a (tricyclic derivatives) through aza‐Diels‐Alder cycloaddition. This strategy will help to construct structurally diverse and bioactive iminosugar analogues.