Reaction of α-Diazopyrroles with Enamines: Synthesis of Pyrrolo[2,1-c][1,2,4]triazines and α-(1,2,5-Triazapenta-1,3-dienyl)pyrroles.

α-Diazopyrroles selectively react with enamines at room temperature to give either (4+2)-cycloaddition-dehydroamination cascade products, pyrrolo[2,1-c][1,2,4]triazines, or azo coupling products. The reaction was used for the synthesis of functionalized ortho-fused heterocycles with new tetrahydrobenzo[e]pyrrolo[2,1-c][1,2,4]triazine and tetrahydro-6H-cyclohepta[e]pyrrolo[2,1-c][1,2,4]triazine frameworks. Unstable azo compounds, 2-[(2-aminovinyl)diazenyl]pyrroles, were obtained from enamines of tetralone or acyclic ketones. According to the density functional theory calculations, (4+2)-cycloaddition of α-diazopyrroles with enamines proceeds in a nonconcerted manner via the zwitterionic intermediate, which undergoes cyclization to pyrrolotriazine or a competitive 1,5-prototropic shift leading to the formation of azo coupling product.