One-Pot Synthesis of Benzo[b][1,4]oxazins via Intramolecular Trapping Iminoenol.

A highly atom-efficient "one-pot" protocol has been developed to construct multisubstituted 2-hydroxy-benzo[b][1,4]oxazins starting from N-(2-hydroxylaryl)enaminones. This procedure comprises a PIDA-mediated intramolecular iminoenol tautomer trapping reaction, followed by EtN-promoted aerobic oxidative ring construction. In particular, an O molecule from air served as the oxygen source of the hydroxyl group in the titled products. This reaction proceeded smoothly at room temperature under air atmosphere and metal-free conditions.