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.