Copper‐Catalyzed Cascade Cyclization Reactions of Isocyanides with α‐Diazocarbonyls as N‐Terminal Electrophiles: Efficient Synthesis of 2‐Imidazolines and 1,1′‐Biimidazoles

The reactions of α-diazocarbonyls have been extensively studied and widely applied in organic synthesis acting as 1,3-dipoles, metal carbene precursors and C-nucleophiles. However, the utility of the electrophilic capability of their terminal nitrogen has been a challenging problem. Herein, a novel copper-catalyzed cascade cyclization reaction of isocyanides with α-diazocarbonyls as N-terminal electrophiles has been developed for the first time. The reaction involves a sequential intermolecular nucleophilic addition/[3+2] cycloaddition/intramolecular cyclization-ring-opening/elimination procedure and provides a new and efficient method for the construction of imidazolines and biimidazoles in a single step from readily available starting materials under very mild conditions.