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

The diastereoisomeric 2‐substituted 2‐azabicyclo[2.2.1]hept‐5‐enes 2–4 were prepared by aza‐Diels‐Alder 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.