Synthesis of Azepines by a Gold-Catalyzed [4+3] Annulation

Significance

Reported is the synthesis of highly substituted azepines 3 by an Au-catalyzed intermolecular [4+3] annulation of vinyl imines 1 with propargyl esters 2. A picolinic acid derived Au(III) catalyst was the most efficient of those studied. The well investigated substrate scope with respect to both reaction partners showed a wide range of functional group tolerance. Higher yields were obtained with electron-donating aryl substituents on the imine nitrogen, lending evidence for a stepwise mechanism involving nucleophilic attack of the imine into a gold-carbenoid intermediate. The reaction was also extended to heteroaryl imines 4 and 6 to give tricyclic azepines 5 and 7 in good yields.