A decarboxylativeintramolecularaziridination reaction of alkene‐tethered 4H‐isoxazol‐5‐ones with a palladium/phosphine catalyst gave 1‐azabicyclo[3.1.0]hex‐2‐enes in moderate to high yields (see scheme; dba=dibenzylideneacetone). The resulting N‐fused bicyclic aziridines readily reacted with various reagents to afford ring‐opening pyrroline derivatives.