Synthesis of 1,2,4-Triazinones Exploiting the Reactivity of Diazadiene and N-Isocyanate Intermediates

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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(2 H )-ones at room temperature.