1,2,4-Triazinones are useful compounds, but their synthesis
can
be challenging. Herein, we report a strategy to build 1,2,4-triazinones
using α-bromohydrazones to access diazadienes and exploiting
their ability to undergo facile substitution with nitrogen nucleophiles.
The N-isocyanate intermediate formed in situ can
then undergo cyclization to give the desired triazinones. This provides
access to products with various substituents at the 4-position, and
with suitable hydrazone precursors (R
2 = Ph), the cascade reaction yields 1,2,4-triazin-3(2H)-ones at room temperature.