An efficient and simple one‐pot synthesis of structurally diverse novel tetrahydroquinoline‐fused iminosugars was developed through the aza‐Diels‐Alder mechanism. The adaptability of this method has been demonstrated by a variety of imines and d/l‐ribose tosylates, and both, electron‐donating and ‐withdrawing substituted imines proceed well. In addition, this reaction is characterized by simple operation, good yield, and high atom economy. Some synthetic iminosugars showed moderate anti proliferation of HCT116 tumor cells. [ABSTRACT FROM AUTHOR]