Dearomative [4+2] Annulation of Electron-Poor N-Heteroarenes with Azoalkenes for Access to Polycyclic Tetrahydro-1,2,4-triazines

A direct dearomative [4 + 2] annulation of electron-poor N-heteroarenes with azoalkenes generated in situ from alpha- halogeno hydrazones was developed under mild conditions. Accordingly, a series of fused polycyclic tetrahydro-1,2,4-triazines with potential biological activity were obtained in up to 96% yield. Various alpha-halogeno hydrazones and N-heteroarenes, such as pyridines, quinolines, isoquinolines, phenanthridine, and benzothia-zole, were tolerated by this reaction. The general applicability of this method was shown by upscale synthesis and product derivatization.

Automated summary

A direct dearomative [4 + 2] annulation of electron-poor N-heteroarenes with azoalkenes generated in situ from alpha- halogeno hydrazones was developed under mild conditions, leading to the synthesis of fused polycyclic tetrahydro-1,2,4-triazines with potential biological activity in high yields (up to 96%). Various alpha-halogeno hydrazones and N-heteroarenes were successfully used in this reaction, demonstrating the broad applicability of this method.