Photosensitizer‐Free Benzo[1,4]oxazin‐2‐one Synthesis by Continuous‐Flow Photochemistry

We report a photosynthetic method for producing 2H‐benzo[b][1,4]oxazin‐2‐ones from aryl azides and α‐ketoacids. This method is highly sustainable, requiring only visible light irradiation of the substrates and no external additives. Furthermore, we implemented a continuous‐flow system to achieve efficient light irradiation and rapid mixing, significantly improving reaction efficiency and reducing reaction time compared to the batch process. The flow system enabled gram‐scale synthesis. We also demonstrated the utility of the products, by employing the benzo[1,4]oxazin‐2‐one moiety as a directing group for C‐H activation on the 3‐aryl substituent. This green approach highlights the potential for developing environmentally friendly synthetic processes.