[5+2] Cyclization of N,N′‐Cyclic Azomethine Imines with 1,3,5‐Triazines: An Efficient Protocol for the Synthesis of Tetrazepine Derivatives

An unprecedented formal [5+2] cyclization of N,N′‐cyclic azomethine imines with triazines has been realized, which provides a facile access to biologically important 1,2,4,6‐tetrazepine frameworks with overall high yields (up to 98% yield). This methodology is distinguished by not involving a metal catalyst, readily available starting materials, and operational simplicity, which involves the reassembly of two C−N bonds. A novel [5+2] cycloaddition reaction of azomethine imines and 1,3,5‐triazineshas been developed, affording tetrazepine derivatives in moderate to good yields under mild reaction conditions. This simple but efficient protocol features cycloaddition of two reactive species in the absence of a transition‐metal catalyst.