North Eastern Regional Institute of Science and Technology 1 article published in JoVE Chemistry Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles Nagendra Nath Yadav1, Hyun-Joon Ha2 1Department of Chemistry, North Eastern Regional Institute of Science and Technology, 2Department of Chemistry, Hankuk University of Foreign Studies Bicyclic aziridinium ions such as 1-azoniabicyclo[4.1.0]heptane tosylate were generated from 2-[4-tolenesulfonyloxybutyl]aziridine, which was utilized for the preparation of substituted piperidines and azepanes via regio- and stereospecific ring-expansion with various nucleophiles. This highly efficient protocol allowed us to prepare diverse azaheterocycles including natural products such as fagomine, febrifugine analogue and balanol.