Synthesis of dibromo- and tetrabromo-bipyrrolines and their corresponding 2,6-diazasemibullvalene derivatives

Abstract

Treatment of Δ¹-dipyrrolines with NBS afforded α,α′-dibromo-Δ¹-bipyrrolines and α,α,α′,α′-tetrabromo-Δ¹-bipyrrolines respectively with excellent selectivity depending on the amount of NBS. All these multibromo-substituted Δ¹-bipyrrolines could be efficiently transformed into their corresponding 2,6-diazasemibullvalene derivatives via reduction with lithium. An unprecedented rearrangement of 4,8-dibromo-2,6-diazasemibullvalene afforded a new type of bipyrroline derivative.