Absolute Configuration of 2‐Substituted 2‐Azabicyclo[2.2.1]hept‐5‐enes

Abstract
The diastereoisomeric 2‐substituted 2‐azabicyclo[2.2.1]hept‐5‐enes 2–4 were prepared by aza‐DielsAlder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using 1H, 1H‐ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (−)‐5. The absolute configuration of (+)‐1, i.e. (1R), was assigned by CD spectroscopy.