Continuous Flow Synthesis of Benzotriazin-4(3 H )-ones via Visible Light Mediated Nitrogen-Centered Norrish Reaction.

We report a new protocol for the synthesis of substituted benzotriazin-4(3 H )-ones which are underrepresented heterocyclic scaffolds with important pharmacological properties. Our method exploits acyclic aryl triazine precursors that undergo a photocyclization reaction upon exposure to violet light (420 nm). Continuous flow reactor technology is exploited to afford excellent yields in only 10 min residence time with no additives or photocatalysts needed. The underlying reaction mechanism appears to be based on an unprecedented variation of the classical Norrish type II reaction with concomitant fragmentation and formation of N-N bonds. Scalability, process robustness, and green credentials of this intriguing transformation are highlighted.