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.