Catalyst-free and atom-economical [4+3] cycloaddition of azadienes with cyclic azomethine imines for facile synthesis of 1,2,4-triazepines

A catalyst-free and atom-economical [4 ​+ ​3] cycloaddition of azadienes with C,N-cyclic azomethine imines has been developed, providing an efficient and environmentally benign access to 1,2,4-triazepines with high diastereoselectivities and yields. This reaction can be performed in 2-methyltetrahydrofuran under mild conditions smoothly.