Synthesis of α,α,α′,α′-Tetrachloro‑Δ1‑bipyrrolines and 4,8-Dichloro-2,6-diazasemibuvallenes

A series of 4,8-dichloro-2,6-diazasemibullvalenes were synthesized and isolated from the reaction of α,α,α′,α′-tetrachloro-Δ1-bipyrrolines with lithium via C–N bond formation. All those dichlorodiazasemibullvalene derivatives demonstrated extremely rapid aza-Cope rearrangement in solution. An unprecedented skeletal rearrangement of 4,8-dichloro-2,6-diazasemibullvalene derivatives took place, resulting in the formation of a new bipyrroline skeleton.