Azirino[c]imidazolyl ylides in the domino reaction of 2,2-dialkyl-4,6-diaryl-1,3-diazabicyclo[3.1.0]hex-3-enes with dichlorocarbenes. Synthesis of (1RS,5SR, 6RS)-4-(alk-1-enyl)-1,5-diaryl-3,7,7-trichloro-2,4-diazabicyclo[4.1.0]hept-2-enes